Spin-canting-induced improper ferroelectricity and spontaneous magnetization reversal in SmFeO3

Implications of magnetic dilution of PrFeO3 with Bi3+ on its dielectric and magnetic properties

Research on functional oxide ceramics has tremendous translational potential for technological applications. Despite sharing a similar formula, BiFeO3 and REFeO3 (RE = rare earth) perovskites differ widely in structure and properties. The potential of substituting non-magnetic Bi3+ with a stereochemically active 6s2 lone pair in rare-earth ferrites remains largely unexplored. In this work, the consequences of replacing Pr3+ with Bi3+ on the dielectric and magnetic properties of PrFeO3 were investigated by synthesizing the samples using a solution combustion method. The inclusion of bismuth led to local site disorder and promoted the reduction of more amounts of Fe3+ to Fe2+, as verified by Raman and XPS measurements. The higher concentration of Fe2+ resulted in the formation of oxygen vacancies. The band gaps of the pure and Bi-substituted PrFeO3 samples were in the range of 1.90-2.08 eV. The field and temperature-dependent magnetic measurements of Pr1-xBixFeO3 confirmed the magnetic dilution. ZFC and FC measurements at low fields revealed a spin reorientation transition at 101 K in the case of Pr0.70Bi0.30FeO3, which supported the negative exchange bias effect at room temperature. The dielectric constant increased with an increase in bismuth content. Electronic structure calculations with charge density plots revealed the induction of polarization by the electric field in the Bi3+-containing samples. This was also verified through PUND measurements, which showed the existence of intrinsic and switchable polarization (0.17 μC cm-2). The random distribution of the stereochemically active 6s2 lone pair on Bi3+ has been proposed as the reason for the observed polarization.

Persistence of weak ferromagnetism in antiferromagnetic systems on the body-centered octahedral lattice

The possibility of existence of weak ferromagnetism in antiferromagnetic systems on the body-centered octahedral lattice is investigated in the framework of the corresponding spin-1/2J_{1}-J_{2} model in the recursive-lattice approach. The exact solution of the model is found and its phase diagram is determined. The magnetic and thermodynamic properties of all phases are studied, the nature of all phase transitions is established, and an equation that determines the positions of all second-order phase transitions of the model is found. The magnetic and entropy properties of all ground states of the model are also determined. It is shown that the weak ferromagnetism predicted earlier in the pure spin-1/2 antiferromagnetic system on the octahedral lattice remains present even in the case of the model on the body-centered octahedral lattice with antiferromagnetic as well as ferromagnetic interactions between the central site of each elementary octahedron and each of its vertices. However, the presence of the interacting central site suppresses the weak ferromagnetism at very low temperatures, where the standard antiferromagnetic phase emerges. At the same time, the temperature region with the antiferromagnetic phase increases with simultaneous decreasing of the region, where the weak ferromagnetism can be observed, when the strength of the interaction between the central site of each elementary octahedron and each of its vertices increases. Moreover, the phenomenon of weak ferromagnetism disappears completely when this interaction becomes sufficiently stronger than the nearest-neighbor antiferromagnetic interaction between spin variables placed in vertices of each elementary octahedron of the lattice. Moreover, the possibility of the existence of the classical spin-liquid behavior in such magnetic systems is also discussed.

Giant exchange bias field above room temperature in perovskite YbCr1-xFexO3 (x = 0.6-0.9)

Temperature-induced exchange bias is observed in perovskite YbCr1-xFexO3 (x = 0.6-0.9) compounds. This is ascribed to the ferromagnetic (FM) coupling between Fe3+/Cr3+ ions and Yb3+ ions. During demagnetization, the Yb3+ ions will show a tendency to rotate with the direction of the applied magnetic field. However, the antiferromagnetic coupling of Fe3+/Cr3+ ions has a pinning effect, hindering their rotation, and thus producing an exchange bias effect. With increasing Fe3+ ion content, the magnetization and exchange bias field gradually become larger. When x = 0.8 and 0.9, the exchange bias field reaches up to -9.7 kOe and -13.6 kOe at 300 K, respectively. This giant room temperature exchange bias field will be more conducive for practical applications in magnetoelectronic devices.

Gateway toward efficient and miniaturized A 2 B 2O7-type fluorite structure-based energy storage devices

Defect fluorite structure with A ₂ B ₂O₇ composition exhibits an intense potential for utilization in modern smart electrical devices. Efficient energy storage with low loss factors like leakage current makes them a prominent candidate for energy storage applications. Here we report a series of the form Nd_2-2x La_2x Ce₂O₇ with x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, synthesized via a sol-gel auto-combustion route. The fluorite structure of Nd₂Ce₂O₇ is slightly expanded with the incorporation of La without any phase transformation. A gradual replacement of Nd with La causes a decrease in grain size, which increases the surface energy and thus leads to grain agglomeration. The formation of exact composition without any impurity element is confirmed by energy-dispersive X-ray spectra. The polarization versus electric field loops, energy storage efficiency, leakage current, switching charge density, and normalized capacitance, which are considered key features of any ferroelectric material, are comprehensively examined. The highest energy storage efficiency, low leakage current, small switching charge density, and large value of normalized capacitance are observed for pure Nd₂Ce₂O₇. This reveals the enormous potential of the fluorite family for efficient energy storage devices. The temperature-dependent magnetic analysis exhibited very low transition temperatures throughout the series.

Magnetic, electric and toroidal polarization modes describing the physical properties of crystals. NdFeO3 case

The structure and the physical phenomena that occur in a crystal can be described by using a suitable set of symmetry-adapted modes. The classification of magnetic modes in crystals presented in Fabrykiewicz et al. [Acta Cryst. (2021), A77, 327-338] is extended to a classification of electric and toroidal (anapole) modes in crystals. These three classifications are based on magnetic point groups, which are used in two contexts: (i) the magnetic point group of the magnetic crystal class and (ii) the magnetic site-symmetry point group of the Wyckoff position of interest. The classifications for magnetic, electric and toroidal modes are based on the properties of the three generalized inversions: space inversion 1, time inversion 1' and the space-and-time inversion 1'. It is emphasized that none of these three inversions is more important than the other two. A new notation for symmetry operation symbols and magnetic point group symbols is proposed; each operation is presented as a product of one proper rotation and one generalized inversion. For magnetic, electric and toroidal orderings there are 64 modes: three pure ferro(magnetic/electric/toroidal) modes, 13 mixed ferro(magnetic/electric/toroidal) and antiferro(magnetic/electric/toroidal) modes, and 48 pure antiferro(magnetic/electric/toroidal) modes. The proposed classification of modes leads to useful observations: the electric and toroidal modes have many symmetry limitations similar to those already known for the magnetic modes, e.g. a continuous reorientation of the magnetic or electric or toroidal moments is possible only in triclinic or monoclinic symmetry. An antiferro(magnetic/electric/toroidal) ordering with a weak perpendicular ferro(magnetic/electric/toroidal) component is possible only in monoclinic or orthorhombic symmetry. The general classifications of magnetic, electric and toroidal modes are presented for the case of NdFeO₃.

Metal-Organic Precursor Synthesis, Structural Characterization, and Multiferroic Properties of GdFeO3 Nanoparticles

GdFeO₃ nanoparticles were fabricated by a facile metal-organic precursor method using citric acid as a complexing agent. The phase purity and structural analysis by powder X-ray diffraction and FTIR studies indicates that the material is highly crystalline with an orthorhombic structure. Electron microscopic (TEM and SEM) studies of rare earth ferrites reveal worm-shaped nanoparticles with an average grain size of 95 nm. The high-resolution TEM study provides an insightful image, which shows an interplanar spacing of approximately 0.12 nm that corresponds to the (112) crystalline plane. A high surface area of 231.5 m² g^-1 has been achieved with a mesoporous texture, which in turn gives a high dielectric constant. Well-defined hysteresis is obtained with a saturation magnetization of 17.5 emu g^-1, remanent magnetization of 3.9 emu g^-1, and coercive field of -446 Oe. Room-temperature ferroelectricity in GdFeO₃ nanoparticles has been found for the first time with no leaky current and hence may be used in multistate memory devices.

High-Magnetic-Sensitivity Magnetoelectric Coupling Origins in a Combination of Anisotropy and Exchange Striction

Magnetoelectric (ME) coupling is highly desirable for sensors and memory devices. Herein, the polarization (P) and magnetization (M) of the DyFeO₃ single crystal were measured in pulsed magnetic fields, in which the ME behavior is modulated by multi-magnetic order parameters and has high magnetic-field sensitivity. Below the ordering temperature of the Dy³⁺-sublattice, when the magnetic field is along the c-axis, the P (corresponding to a large critical field of 3 T) is generated due to the exchange striction mechanism. Interestingly, when the magnetic field is in the ab-plane, ME coupling with smaller critical fields of 0.8 T (a-axis) and 0.5 T (b-axis) is triggered. We assume that the high magnetic-field sensitivity results from the combination of the magnetic anisotropy of the Dy³⁺ spin and the exchange striction between the Fe³⁺ and Dy³⁺ spins. This work may help to search for single-phase multiferroic materials with high magnetic-field sensitivity.

The magnetic structure of DyFeO3revisited: Fe spin reorientation and Dy incommensurate magnetic order

High resolution and high intensity neutron powder diffraction is used to study the ground state magnetic order and the spin reorientation transition in the orthoferrite DyFeO₃. The transition from the high temperaturek= 0 Γ₄(G_xA_yF_z) to the low temperature Γ₁(A_xG_yC_z) type order of the Fe-sublattice is found atT_SR= 73 K and does not show any thermal hysteresis. BelowT_N2= 4 K the Dy-sublattice orders in an incommensurate magnetic structure withk= [0, 0, 0.028] while the Fe-sublattice keeps its commensurate Γ₁type order. DyFeO₃is the first orthoferriteRFeO₃to possess an incommensurate magnetic order of the rare earth sublattice under zero field conditions; an important piece of information neglected in the recent discussion of its multiferroic properties.

Role of oxygen vacancies in colossal polarization in SmFeO3-δ thin films

The orthorhombic rare-earth manganates and ferrites multiferroics are promising candidates for the next generation multistate spintronic devices. However, their ferroelectric polarization is small, and transition temperature is far below room temperature (RT). The improvement of ferroelectricity remains challenging. Here, through the subtle strain and defect engineering, an RT colossal polarization of 4.14 μC/cm2 is achieved in SmFeO3-δ films, which is two orders of magnitude larger than its bulk and is also the largest one among the orthorhombic rare-earth manganite and ferrite family. Meanwhile, its RT magnetism is uniformly distributed in the film. Combining the integrated differential phase-contrast imaging and density functional theory calculations, we reveal the origin of this superior ferroelectricity in which the purposely introduced oxygen vacancies in the Fe-O layer distorts the FeO6 octahedral cage and drives the Fe ion away from its high-symmetry position. The present approach can be applied to improve ferroelectric properties for multiferroics.

Chemical design of a new displacive-type ferroelectric

Since the discovery of the ferroelectric perovskite-type oxide BaTiO₃ in 1943, numerous materials have been surveyed as candidates for new ferroelectrics. Perovskite-type materials have played a leading role in basic research and applications of ferroelectric materials since the last century. Experimentalists and theoreticians have developed a new materials design stream for post-perovskite materials. In this stream, we have mainly focused on the role of covalency in the evolution of ferroelectricity for displacive-type ferroelectrics in oxides. This perspective surveys the following topics: (1) crossover from quantum paraelectric to ferroelectric through a ferroelectric quantum critical point, (2) the role of cation-oxygen covalency in ferroelectricity and the crossover to quantum paraelectric in perovskite-type compounds, (3) off-center-induced ferroelectricity in perovskites, (4) second-order Jahn-Teller effect enhancement of ferroelectricity in lithium-niobate-type oxides, (5) the presence of four ferroelectric phases and structural transitions of phases of AFeO₃ with decreasing radius of A (A = La-Al), (6) tetrahedral ferroelectrics of perovskite-related Bi₂SiO₅ and wurtzites, (7) a rare type of polarization switching system in which the coordination number of ions in κ-Al₂O₃ systems changes between 4 and 6, and (8) lone-pair-electron-induced ferroelectrics in langasite-type compounds.

Low field control of spin switching and continuous magnetic transition in an ErFeO3 single crystal

The magnetic behavior of a rare-earth orthoferrite ErFeO₃ single crystal can be controlled by low magnetic fields from a few to hundreds of Oe. Here we investigated a high-quality ErFeO₃ single crystal in the temperature range of 5-120 K, with two types of spin switching in the field-cooled-cooling (FCC) and field-cooled-warming (FCW) processes below the temperature of the spin reorientation (SR) transition from Γ₄ to Γ₂ at 98-88 K. The magnitude of the applied magnetic fields can regulate two types of spin switching along the a-axis of the ErFeO₃ single crystal but does not affect the type and temperature range of the SR transition. An interesting "multi-step" type-II spin switching is observed in FCW under low magnetic fields (H < 18 Oe) just below the SR transition temperature, which is associated with the interaction and the change of magnetic configurations from rare-earth and iron magnetic sublattices. When the magnetic field is lower than 15 Oe, the type-II spin switching in the FCW process gradually changes to a continuous magnetic transition along the a-axis of the ErFeO₃ single crystal. As the magnetic field is reduced to less than 17 Oe, the type-I spin switching in the FCW process also transforms into a continuous magnetic transition. Understanding the magnetic reversal effects will help us explore the potential applications of these magnetic materials for future information devices.

An antisite defect mechanism for room temperature ferroelectricity in orthoferrites

Single-phase multiferroic materials that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, motivating an ongoing search for mechanisms for unconventional ferroelectricity in magnetic oxides. Here, we report an antisite defect mechanism for room temperature ferroelectricity in epitaxial thin films of yttrium orthoferrite, YFeO₃, a perovskite-structured canted antiferromagnet. A combination of piezoresponse force microscopy, atomically resolved elemental mapping with aberration corrected scanning transmission electron microscopy and density functional theory calculations reveals that the presence of Y_Fe antisite defects facilitates a non-centrosymmetric distortion promoting ferroelectricity. This mechanism is predicted to work analogously for other rare earth orthoferrites, with a dependence of the polarization on the radius of the rare earth cation. Our work uncovers the distinctive role of antisite defects in providing a mechanism for ferroelectricity in a range of magnetic orthoferrites and further augments the functionality of this family of complex oxides for multiferroic applications.

Doping tuned spin reorientation and spin switching in praseodymium-samarium orthoferrite single crystals

We investigate the detailed analysis of the magnetic properties in a series of Pr_1-xSm_xFeO₃single crystals fromx= 0 to 1 with an interval of 0.1. Doping controlled spin reorientation transition temperatureT_SRΓ₄(G_x,A_y,F_z) to Γ₂(F_x,C_y,G_z) covers a wide temperature range including room temperature. A 'butterfly'-shape type-I spin switching with 180° magnetization reversal occurs below and above the magnetization compensation points inx= 0.4 to 0.8 compounds. Interestingly, in Pr_0.6Sm_0.4FeO₃single crystal, we find an inadequate spin reorientation transition accompanied by uncompleted type-I spin switching in the temperature region from 138 to 174 K. Furthermore, a type-II spin switching appears at 23 K, as evidenced from the magnetization curve in field-cooled-cooling (FCC) mode initially bifurcate from zero-field-cooled (ZFC) magnetization curve at 40 K and finally drops back to coincide the ZFC magnetization value at 23 K. Our current research reveals a strong and complex competition between Pr³⁺-Fe³⁺and Sm³⁺-Fe³⁺exchange interactions and more importantly renders a window to design spintronic device materials for future potential applications.

Determination of the magnetic structures in orthoferrite CeFeO3by neutron powder diffraction: first order spin reorientation and appearance of an ordered Ce-moment

High resolution and high intensity neutron powder diffraction are used to determine the temperature dependence of the crystallographic and magnetic structure of the orthoferrite CeFeO₃. The high temperatureG_x-type magnetic coupling of the Fe-sublattice described by the Γ₄(G_xA_yF_z) irreducible representation changes at the spin reorientation temperatureT_SR= 228 K to aG_y-type coupling of Γ₁(A_xG_yC_z). The spin reorientation is of first order and sees a hysteresis of about 2.5 K atT_SR. Below 35 K faint magnetic peaks reflectingC_ztype magnetic coupling appear and are argued to be related to the Ce-sublattice. Magnetic moments at 2 K amount toμ_Fe= 4.15 μ_Bandμ_Ce= 0.11 μ_B. CeFeO₃is only the secondRFeO₃compound after DyFeO₃showing this ground state magnetic structure of the Fe-sublattice. The orthorhombic structurePbnmis kept over the whole temperature range.

Enhanced Spin-Orbit Coupled Photoluminescence of Perovskite CsPbBr3 Quantum Dots by Piezo-Phototronic Effect

Piezo-phototronic effect is a fundamental effect of semiconductors lacking of central symmetry with geometries from one-dimensional (1D) nanowire to 3D bulk. Here, we present that the piezo-phototronic effect can even tune a spin-orbit coupled photoluminescence (PL) based on all-inorganic perovskite CsPbBr₃ quantum dots (QDs). Although the cubic structure of CsPbBr₃ QDs is nonpiezoelectric, a cooling treatment can change it to an orthorhombic structure, which is proven to possess a piezoelectric property. The spin-orbit coupled PL intensity is demonstrated to be dependent on the polarization of the excited light. Because of the manipulation of the spin-split energy levels via the piezo-phototronic effect, the spin-orbit coupled PL intensities under a -0.9% compressive strain for linearly and circularly polarized light excitations can be enhanced by 136% and 146%, respectively. These findings reveal fundamental understandings of the spin-orbit coupled PL dynamics and demonstrate promising optoelectronic applications of the piezo-phototronic effect in these QDs.

Chemical Sensitivity of Kβ and Kα X-ray Emission from a Systematic Investigation of Iron Compounds

K-fluorescence X-ray emission spectroscopy (XES) is receiving growing interest in all fields of natural sciences to investigate the local spin. The spin sensitivity in Kβ (Kα) XES stems from the exchange interaction between the unpaired 3p (2p) and the 3d electrons, which is greater for Kβ than for Kα. We present a thorough investigation of a large number of iron-bearing compounds. The experimental spectra were analyzed in terms of commonly used quantitative parameters (Kβ_1,3-first moment, Kα₁-full width at half-maximum, and integrated absolute difference -IAD-), and we carefully examined the difference spectra. Multiplet calculations were also performed to elucidate the underlying mechanisms that lead to the chemical sensitivity. Our results confirm a strong influence of covalency on both Kβ and Kα lines. We establish a reliable spin sensitivity of Kβ XES as it is dominated by the exchange interaction, whose variations can be quantified by either Kβ_1,3-first moment or Kβ-IAD and result in a systematic difference signal line shape. We find an exception in the Kβ XES of Fe³⁺ and Fe²⁺ in water solution, where a new difference spectrum is identified that cannot be reproduced by scaling the exchange integrals. We explain this by strong differences in orbital mixing between the valence orbitals. This result calls for caution in the interpretation of Kβ XES spectral changes as due to spin variations without a careful analysis of the line shape. For Kα XES, the smaller exchange interaction and the influence of other electron-electron interactions make it difficult to extract a quantity that directly relates to the spin.

Spin reorientation transition and coupled spin-lattice dynamics of Sm0.6Dy0.4FeO3

In this work, we have presented a solid-solution of Sm0.6Dy0.4FeO3in the form of nano-particles having spin reorientation transition (SRT) at a temperature interval of 220-260 K. The lattice dynamics of Sm0.6Dy0.4FeO3have investigated by temperature-dependent x-ray diffraction and Raman spectroscopy. A negative thermal expansion at low temperatures has observed, which might be due to the interaction between Sm3+and Fe3+sublattice. Anomalous behavior in lattice parameters, octahedral tilt angle, and bond lengths have observed in the vicinity of SRT, which confirms the existence of magneto-elastic coupling in the system. The strong anomaly has observed in linewidth and phonon frequencies of Raman modes around SRT, which may be related to the spin-phonon coupling in Sm0.6Dy0.4FeO3. The contribution of SRT in lattice change and the presence of spin-phonon coupling can help to understand the correlation between the magnetic and structural properties of orthoferrite.

Enhancement of magnetoelectric coupling in Cr doped Mn2O3

The effect of Cr doping has been undertaken to investigate its effect on the structural, magnetic, dielectric and magnetoelectric properties of newly discovered multiferroics material α-Mn₂O₃. The Cr doping modifies the room temperature crystal symmetry i.e. transforms from orthorhombic to cubic symmetry. Similar to α-Mn₂O₃, two magnetic transitions have been observed in all Cr doped samples. The effect of Cr doping manifested on the low temperature transition. The lower magnetic transition shifted toward higher temperature (25 K for pristine to 40 K for Cr = 10%) whereas the high temperature transition decreases slightly with increasing Cr content. A clear frequency independent transition is observed in temperature dependent complex dielectric measurements for Mn_2-x Cr _x O₃ (0 ⩽ x ⩽ 0.10) samples around high temperature magnetic ordering ∼80 K which corroborate the magnetoelectric coupling in these samples. Interestingly, the magnetodielectric value enhanced significantly with Cr doping and a maximum increase of ∼21% is observed for 10% Cr doped sample at 5 K around 70 kOe magnetic field.

Structural, optical and magnetic properties of Sm3+ doped yttrium orthoferrite (YFeO3) obtained by sol-gel synthesis route

Fine powders of Y_1-x Sm _x FeO₃ (x  =  0, 0.05, 0.10, 0.15) were synthesized via citrate based sol-gel route. While the as synthesized powders were amorphous, the calcined (900 °C/8 h) powders were confirmed to be polycrystalline by x-ray powder diffraction (XRD) studies. The calcined powders were found to crystallize in an orthorhombic structure associated with the lattice parameters a  =  5.59 Å, b  =  7.60 Å, c  =  5.28 Å. These lattice parameters increased with the increase in Sm³⁺ content at yttrium sites. The strain that was obtained by the Williamson-Hall method increased with the increase in dopant (Sm³⁺) concentration vis-à-vis a decrease in crystallite size. Diffuse reflectance spectroscopic studies suggest an increase in band gap as Sm doping level increased. Significant enhancement in magnetization associated with a decrease in coercive field accompanied by a transition from anti-ferromagnetic to soft ferromagnetic behaviour in Sm doped YFeO₃ were encountered. It is hoped that these materials with the enhanced magnetic properties could be of potential use for multifarious applications.

Investigating the anisotropic compression and high-pressure phase symmetry of orthorhombic RFeO3 vs RMnO3

Rare-earth orthoferrites and orthomanganites present strong couplings between their structural distortions and physical properties, namely magnetoelectricity, generating interest in predicting and realizing new phases under external parameters, such as hydrostatic pressure. In this regard, we discuss the differences and the similarities of the high-pressure behaviour of the structural distortions arising from anisotropic volume compression. This allows a better understanding of the role played by the octahedra tilt and Jahn-Teller effect as pressure accommodation mechanisms on the stabilization of different crystallographic phases after the insulator to metal structural transition occurring at the critical pressures (Pc) between 35 and 50 GPa.

Spin structure and spin Hall magnetoresistance of epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO3

We report a combined study of imaging the antiferromagnetic (AFM) spin structure and measuring the spin Hall magnetoresistance (SMR) in epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO₃. X-ray magnetic linear dichroism photoemission electron microscopy measurements reveal that the AFM spins of the SmFeO₃(1 1 0) align in the plane of the film. Angularly dependent magnetoresistance measurements show that SmFeO₃/Ta bilayers exhibit a positive SMR, in contrast to the negative SMR expected in previously studied collinear AFMs. The SMR amplitude increases linearly with increasing external magnetic field at higher magnetic fields, suggesting that field-induced canting of the AFM spins plays an important role. In contrast, around the coercive field, no detectable SMR signal is observed, indicating that the SMR of the AFM and canting magnetization components cancel out. Below 50 K, the SMR amplitude increases sizably by a factor of two as compared to room temperature, which likely correlates with the long-range ordering of the Sm ions. Our results show that the SMR is a sensitive technique for non-equilibrium spin systems of non-collinear AFMs.

Spin switching temperature modulated by the magnetic field and spontaneous exchange bias effect in single crystal SmFeO3

The spin switching and exchange bias effect were investigated in the rare earth orthoferrite SmFeO₃ composed of two antiferromagnetically coupled sublattices Sm³⁺ and Fe³⁺ with canted ferromagnetic moments and a temperature induced spin switching in single crystal SmFeO₃ was observed. The spin switching temperature was found to be modulated by exerting different magnetic fields below the compensation temperature ([Formula: see text]). This effect could be explained as the changes of energy barrier related to the magnetization direction under different magnetic fields. In the meantime, the coercivity displayed strong dependence on the maximum applied magnetic fields in the hysteresis measurement. In addition, spontaneous exchange bias effect (EB) was observed with the largest EB field value of 1.2 T, and the EB field changed its sign across the compensation point. Our results indicate that the magnetic properties of SmFeO₃ can be strongly affected and controlled by the temperature or the applied magnetic field during the measurement process, and it might lead to novel applications in magneto-optics, ultrafast switching, and magnetic sensing devices.

Spin-lattice correlation in Eu3+ doped antiferromagnet TmFeO3

We report the physical properties of Eu-doped bulk TmFeO₃ through X-ray diffraction, magnetic susceptibility (χ), Raman scattering and X-ray absorption spectroscopy (XAS) study, which shows a similar orthorhombic structure with the Pbnm space group as TmFeO₃. Magnetic measurement on Eu-doped TmFeO₃ provides evidence for spin reorientations of Fe³⁺. Further, the Raman spectra of Eu³⁺ doped TmFeO₃ show significant changes in Raman modes as a function of temperature, which are evidence for strong spin-lattice interaction. From the XAS spectra, the L-edge of Fe provides information on the valence state of Fe, whereas the K-edge of oxygen shows that the compound has a strong influence on the hybridization of the O(2p) state with the 3d states of Fe.

Large easy-plane anisotropy induced spin reorientation in magnetoelectric materials (Co4-x Mn x )Nb2O9

Neutron powder diffraction experiments were carried out on the magnetoelectric compound series (Co_4-x Mn _x )Nb₂O₉ (x  =  0, 1, 2, 3, 3.5, 3.9, 3.95 and 4) from base temperature to above their Néel temperatures. Their magnetic structures were analysed by using the irreducible representation analysis and Rietveld refinement method. Similar to Co₄Nb₂O₉, the compounds with x  ⩽  3.9 have noncollinear in-plane magnetic structures (Γ6) with magnetic moments lying purely in the ab plane with certain canting angles. Mn₄Nb₂O₉ has a collinear antiferromagnetic structure (Γ2) with magnetic moments aligning along the c axis. The compound of x  =  3.95 shows two magnetic phases in the magnetization, which was confirmed to have the Γ2 magnetic structure above 60 K and develop a second Γ6 local phase in addition to the main Γ2 phase due to doping. This study indicates 2.5 at% Co²⁺ doping is sufficient to alter the collinear easy-axis magnetic structure of Mn₄Nb₂O₉ into the noncollinear easy-plane magnetic structure, which is attributed to the large easy-plane anisotropy of Co²⁺ and relative small Ising-like anisotropy of Mn²⁺. The doping effects on the Néel temperature and occupancy are also discussed.

Manipulate the Electronic and Magnetic States in NiCo2 O4 Films through Electric-Field-Induced Protonation at Elevated Temperature

Ionic-liquid-gating- (ILG-) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the study of a wide range of systems (e.g., SrCoO_2.5 , VO₂ , WO₃ , etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo₂ O₄ , an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo₂ O₄ from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG-induced ionic evolution.

Strong magnetoelectric coupling in mixed ferrimagnetic-multiferroic phases of a double perovskite

Exploring new magnetic materials is essential for finding advantageous functional properties such as magnetoresistance, magnetocaloric effect, spintronic functionality, and multiferroicity. Versatile classes of double perovskite compounds have been recently investigated because of intriguing physical properties arising from the proper combination of several magnetic ions. In this study, it is observed that the dominant ferrimagnetic phase is coexisted with a minor multiferroic phase in single-crystalline double-perovskite Er₂CoMnO₆. The majority portion of the ferrimagnetic order is activated by the long-range order of Er³⁺ moments below T_Er = 10 K in addition to the ferromagnetic order of Co²⁺ and Mn⁴⁺ moments arising at T_C = 67 K, characterized by compensated magnetization at T_Comp = 3.15 K. The inverted magnetic hysteresis loop observed below T_Comp can be described by an extended Stoner-Wohlfarth model. The additional multiferroic phase is identified by the ferroelectric polarization of ~0.9 μC/m² at 2 K. The coexisting ferrimagnetic and multiferroic phases appear to be strongly correlated in that metamagnetic and ferroelectric transitions occur simultaneously. The results based on intricate magnetic correlations and phases in Er₂CoMnO₆ enrich fundamental and applied research on magnetic materials through the scope of distinct magnetic characteristics in double perovskites.

Synthesis, Structure, and Physical Properties of the Polar Magnet DyCrWO6

It has recently been reported that the ordered aeschynite-type polar ( Pna2₁) magnets RFeWO₆ (R = Eu, Tb, Dy, Y) exhibit type II multiferroic properties below T_N ∼ 15-18 K. Herein, we report a comprehensive investigation of the isostructural oxide DyCrWO₆ and compare the results with those of DyFeWO₆. The cation-ordered oxide DyCrWO₆ crystallizes in the same polar orthorhombic structure and undergoes antiferromagnetic ordering at T_N = 25 K. Contrary to DyFeWO₆, only a very weak dielectric anomaly and magnetodielectric effects are observed at the Néel temperature and, more importantly, there is no induced polarization at T_N. Furthermore, analysis of the low-temperature neutron diffraction data reveals a collinear arrangement of Cr spins but a noncollinear Dy-spin configuration due to single-ion anisotropy. We suggest that the collinear arrangement of Cr spins may be responsible for the absence of electric polarization in DyCrWO₆. A temperature-induced magnetization reversal and magnetocaloric effects are observed at low temperatures.

Low-energy spin dynamics of orthoferrites AFeO3 (A = Y, La, Bi)

YFeO₃ and LaFeO₃ are members of the rare-earth orthoferrites family with Pbnm space group. Using inelastic neutron scattering, the low-energy spin excitations have been measured around the magnetic Brillouin zone center. Splitting of magnon branches and finite magnon gaps (∼2 meV) are observed for both compounds, where the Dzyaloshinsky-Moriya interactions account for most of this gap with some additional contribution from single-ion anisotropy. We also make comparisons with multiferroic BiFeO₃ (R3c space group), in which similar behavior was observed. By taking into account all relevant local Dzyaloshinsky-Moriya interactions, our analysis allows for the precise determination of all experimentally observed parameters in the spin-Hamiltonian. We find that different properties of the Pbnm and R3c space group lead to the stabilization of a spin cycloid structure in the latter case but not in the former, which explains the difference in the levels of complexity of magnon band structures for the respective compounds.

Intrinsic structural distortion and exchange interactions in SmFe x Cr1-x O3 compounds

The effect of substituting different amounts of magnetic metal Fe on the magnetic properties of SmFe_xCr_1−xO₃ (0 < x < 0.5) is reported here in order to probe the relation between the structural distortion and magnetism in these materials. The structural properties of the samples were characterized using X-ray diffraction with Rietveld refinements, and Raman spectroscopy carried out at ambient temperature. Magnetization data reveals the Neel temperature (T_N, where the Cr(Fe) ions order) increases with an increase in the average B-site ionic radius, and average Cr(Fe)–O–Cr(Fe) bond angle. By fitting the temperature dependence of the magnetic susceptibility to the Curie–Weiss law modified by the Dzyaloshinskii–Moriya (DM) interaction, the strengths of the symmetric and antisymmetric Cr(Fe)–Cr(Fe) exchange interactions (J and D) were determined. It was found that the strength of the symmetric interaction J (reflected in the changes in the Neel temperature) increases with the replacement of Cr³⁺ with Fe³⁺, which is ascribed to the changes in the average Cr(Fe)–O–Cr(Fe) bond angle and bond lengths. Meanwhile, the antisymmetric interaction D a slightly decreases, which may be ascribed to the displacement of oxygen ions (dO) away from their “original” middle point.

The relationship between intrinsic structural distortions and exchange interactions in SmFe_xCr_1−xO₃ compounds was studied.

Structure Peculiarities of Micro- and Nanocrystalline Perovskite Ferrites La1-x Sm x FeO3

Micro- and nanocrystalline lanthanum-samarium ferrites La_1-x Sm _x FeO₃ with orthorhombic perovskite structure were obtained by using both solid state reactions (x = 0.2, 0.4, 0.6 and 0.8) and sol-gel synthesis (x = 0.5) techniques. Obtained structural parameters of both series of La_1-x Sm _x FeO₃ are in excellent agreement with the "pure" LaFeO₃ and SmFeO₃ compounds, thus proving formation of continuous solid solution in the LaFeO₃-SmFeO₃ system. Peculiarity of La_1-x Sm _x FeO₃ solid solution is divergence behaviour of unit cell dimensions with increasing x: systematic decrease of the a and c lattice parameters is accompanied with increasing b parameter. Such behaviour of the unit cell dimensions in La_1-x Sm _x FeO₃ series led to crossover of the a and c perovskite lattice parameters and formation of dimensionally tetragonal structure near x = 0.04. Linear decrease of the unit cell volume of La_1-x Sm _x FeO₃ with decreasing x according with the Vegard's rule indicate absence of short-range ordering of R-cations in the LaFeO₃-SmFeO₃ system.

Single crystal polarized neutron diffraction study of the magnetic structure of HoFeO3

Polarised neutron diffraction measurements have been made on HoFeO₃ single crystals magnetised in both the [0 0 1] and [1 0 0] directions (Pbnm setting). The polarisation dependencies of Bragg reflection intensities were measured both with a high field of [Formula: see text] T parallel to [0 0 1] at [Formula: see text] K and with the lower field [Formula: see text] T parallel to [1 0 0] at [Formula: see text] K. A Fourier projection of magnetization induced parallel to [0 0 1], made using the hk0 reflections measured in 9 T, indicates that almost all of it is due to alignment of Ho moments. Further analysis of the asymmetries of general reflections in these data showed that although, at 70 K, 9 T applied parallel to [0 0 1] hardly perturbs the antiferromagnetic order of the Fe sublattices, it induces significant antiferromagnetic order of the Ho sublattices in the [Formula: see text] plane, with the antiferromagnetic components of moment having the same order of magnitude as the induced ferromagnetic ones. Strong intensity asymmetries measured in the low temperature [Formula: see text] structure with a lower field, 0.5 T [Formula: see text] [1 0 0] allowed the variation of the ordered components of the Ho and Fe moments to be followed. Their absolute orientations, in the [Formula: see text] domain stabilised by the field were determined relative to the distorted perovskite structure. This relationship fixes the sign of the Dzyalshinski-Moriya (D-M) interaction which leads to the weak ferromagnetism. Our results indicate that the combination of strong y-axis anisotropy of the Ho moments and Ho-Fe exchange interactions breaks the centrosymmetry of the structure and could lead to ferroelectric polarization.

Spin-reorientation magnetic transitions in Mn-doped SmFeO3

Spin reorientation is a magnetic phase transition in which rotation of the magnetization vector with respect to the crystallographic axes occurs upon a change in the temperature or magnetic field. For example, SmFeO3 shows a magnetization rotation from the c axis above 480 K to the a axis below 450 K, known as the Γ4 → Γ2 transition. This work reports the successful synthesis of the new single-crystal perovskite SmFe0.75Mn0.25O3 and finds interesting spin reorientations above and below room temperature. In addition to the spin reorientation of the Γ4 → Γ2 magnetic phase transition observed at around TSR2 = 382 K, a new spin reorientation, Γ2 → Γ1, was seen at around TSR1 = 212 K due to Mn doping, which could not be observed in the parent rare earth perovskite compound. This unexpected spin configuration has complete antiferromagnetic order without any canting-induced weak ferromagnetic moment, resulting in zero magnetization in the low-temperature regime. M-T and M-H measurements have been made to study the temperature and magnetic-field dependence of the observed spin reorientation transitions.

Improper electric polarization in simple perovskite oxides with two magnetic sublattices

ABO₃ perovskite oxides with magnetic A and B cations offer a unique playground to explore interactions involving two spin sublattices and the emergent effects they may drive. Of particular interest is the possibility of having magnetically driven improper ferroelectricity, as in the much studied families of rare-earth orthoferrites and orthochromites; yet, the mechanisms behind such effects remain to be understood in detail. Here we show that the strongest polar order corresponds to collinear spin configurations and is driven by non-relativistic exchange-strictive mechanisms. Our first-principles simulations reveal the dominant magnetostructural couplings underlying the observed ferroelectricity, including a striking magnetically driven piezoelectric effect. Further, we derive phenomenological and atomistic theories that describe such couplings in a generic perovskite lattice. This allows us to predict how the observed effects can be enhanced, and even how similar ones can be obtained in other perovskite families.

Magnetically-driven ferroelectricity holds the key for novel multiferroic effects in perovskite oxides, but it remains poorly understood. Here, Zhao et al. determine the dominant magnetostructural couplings that yield improper ferroelectricity in a generic perovskite with two spin sublattices.

Sm/Ti co-substituted bismuth ferrite multiferroics: reciprocity between tetragonality and piezoelectricity

BiFeO₃ (BFO) systems co-modified with Ti, Sm and Sm–Ti have been investigated for piezoelectricity together with dielectric and multiferroic properties.

Thermal Behaviour of Sm0.5 R 0.5FeO3 (R = Pr, Nd) Probed by High-Resolution X-ray Synchrotron Powder Diffraction

Mixed ferrites Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 with orthorhombic perovskite structure isotypic with GdFeO3 were synthesized by solid-state reaction technique in air at 1473 K. Structural parameters obtained at room temperature prove a formation of continuous solid solutions in the SmFeO3-PrFeO3 and SmFeO3-NdFeO3 pseudo-binary systems. Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 show strongly anisotropic nonlinear thermal expansion: thermal expansion in the b direction is twice lower than in the a and c directions. The average linear thermal expansion coefficients of Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 in the temperature range of 298-1173 K are in the limits of (9.0-11.1) × 10(-6) K(-1), which is close to the values reported for the parent RFeO3 compounds. Subtle anomalies in the lattice expansion of Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 detected at 650-750 K reflect magnetoelastic coupling at the magnetic ordering temperature T N.

Implementing Room-Temperature Multiferroism by Exploiting Hexagonal-Orthorhombic Morphotropic Phase Coexistence in LuFeO3 Thin Films

Room-temperature multiferroism in LuFeO3 (LFO) films is demonstrated by exploiting the orthorhombic-hexagonal (o-h) morphotrophic phase coexistence. The LFO film further reveals a magnetoelectric coupling effect that is not shown in single-phase (h- or o-) LFO. The observed multiferroism is attributed to the combination of sufficient polarization from h-LFO and net magnetization from o-LFO.

Non-collinear magnetism in multiferroic perovskites

We present an overview of the current interest in non-collinear magnetism in multiferroic perovskite crystals. We first describe the different microscopic mechanisms giving rise to the non-collinearity of spins in this class of materials. We discuss, in particular, the interplay between non-collinear magnetism and ferroelectric and antiferrodistortive distortions of the perovskite structure, and how this can promote magnetoelectric responses. We then provide a literature survey on non-collinear multiferroic perovskites. We discuss numerous examples of spin cantings driving weak ferromagnetism in transition metal perovskites, and of spin-induced ferroelectricity as observed in the rare-earth based perovskites. These examples are chosen to best illustrate the fundamental role of non-collinear magnetism in the design of multiferroicity.

Tailoring the magnetic and magnetoelectric properties of rare earth orthoferrites for room temperature applications

The M(T) curve shows negative magnetization value for samples containing Er ions. The dielectric constant value does not show any anomaly around the magnetic transition temperature. The temperature at which maximum MDE effect observed corresponds to dielectric loss maxima.

Tunable room temperature magnetoelectric response of SmFeO3/poly(vinylidene fluoride) nanocomposite films

SmFeO₃/poly(vinylidene fluoride) composite films exhibit tunable magnetoelectric effects induced by strong strain interactions at the interfaces.

Ultralow temperature terahertz magnetic thermodynamics of perovskite-like SmFeO3 ceramic

The terahertz magnetic properties of perovskite-like SmFeO₃ ceramic are investigated over a broad temperature range, especially at ultralow temperatures, using terahertz time-domain spectroscopy. It is shown that both resonant frequencies of quasi-ferromagnetic and quasi-antiferromagnetic modes have blue shifts with the decreasing temperature due to the enhancement of effective magnetic field. The temperature-dependent magnetic anisotropy constants are further estimated using the resonant frequencies, under the approximation of omitting the contribution of Sm³⁺ magnetic moments to the effective field. Specially, the effective anisotropy constants in the ca and cb planes at 3 K are 6.63 × 10⁵ erg/g and 8.48 × 10⁵ erg/g, respectively. This thoroughly reveals the terahertz magnetic thermodynamics of orthoferrites and will be beneficial to the application in terahertz magnetism.

Upgrade of beamline BL08B at Taiwan Light Source from a photon-BPM to a double-grating SGM beamline

During the last 20 years, beamline BL08B has been upgraded step by step from a photon beam-position monitor (BPM) to a testing beamline and a single-grating beamline that enables experiments to record X-ray photo-emission spectra (XPS) and X-ray absorption spectra (XAS) for research in solar physics, organic semiconductor materials and spinel oxides, with soft X-ray photon energies in the range 300-1000 eV. Demands for photon energy to extend to the extreme ultraviolet region for applications in nano-fabrication and topological thin films are increasing. The basic spherical-grating monochromator beamline was again upgraded by adding a second grating that delivers photons of energy from 80 to 420 eV. Four end-stations were designed for experiments with XPS, XAS, interstellar photoprocess systems (IPS) and extreme-ultraviolet lithography (EUVL) in the scheduled beam time. The data from these experiments show a large count rate in core levels probed and excellent statistics on background normalization in the L-edge adsorption spectrum.