A reentrant phenomenon in magnetic and dielectric properties of Dy2BaNiO5 and an intriguing influence of external magnetic field

Green sonochemical synthesis of BaDy2NiO5/Dy2O3 and BaDy2NiO5/NiO nanocomposites in the presence of core almond as a capping agent and their application as photocatalysts for the removal of organic dyes in water

The present work reports the sonochemical synthesis of DBNO NC (dysprosium nickelate nanocomposite) using metal nitrates and core almond as a capping agent. In addition, the effects of the power of ultrasound irradiation were investigated. The BaDy2NiO5/Dy2O3 and BaDy2NiO5/NiO nanocomposites were synthesized with sonication powers of 50 and 30 W, respectively. The agglomerated nanoparticles were obtained using different sonication powers, including 15, 30, and 50 W. The results showed that upon increasing the sonication power, the particle size decreased. After characterization, the optical, electrical, magnetic, and photocatalytic properties of the NC were studied. The nanocomposites showed an antiferromagnetic behavior. In this study, the photocatalytic degradations of two dyes, AR14 and AB92, were investigated in the presence of DBNO NC. Furthermore, the effects of the amount of photocatalyst, the concentration of the dye solution, the type of organic dye, and light irradiation on the photocatalytic activity of the nanocomposite were studied. The results showed that with an increasing amount of catalyst and decreasing concentration of dye, the photocatalytic activity of the nanocomposite was increased. This activity for the degradation of AR14 is higher than that of AB92. Both AR14 and AB92 dyes show higher photocatalytic degradation under UV irradiation than under Vis irradiation.

Destruction of multiferroicity in Tb2BaNiO5 by Sr-doping and its implication to magnetodielectric coupling

The Haldane spin-chain compound, Tb₂BaNiO₅, with two antiferromagnetic transitions, one at T ₁  =  63 K and the other at T ₂  =  25 K, has been recently shown to be an exotic multiferroic below T ₂. Here, we report the results of our investigation of Sr doping at the Ba site by magnetization, heat-capacity, magnetodielectric (MDE) and pyrocurrent measurements. An intriguing finding, which we stress, is that the ferroelectricity is lost even for a doping level of ten atomic percent, though magnetic ordering prevails. The doped specimens however retain significant MDE behaviour, but with reduced magnitudes and qualitative changes with respect to the behaviour of the parent compound. This implies that ferroelectric order is also crucial for the anomalously large MDE in the parent compound, in addition to the role of 4f single-ion anisotropy.

Observation of magnetoelastic and magnetoelectric coupling in Sc doped BaFe12O19 due to spin-glass-like phase

The present work reports magnetic, magnetoelastic and magnetoelectric (ME) response of scandium (Sc) doped barium hexaferrite, BaFe₁₀Sc₂O₁₉. DC magnetization shows that partial substitution of non-magnetic Sc for Fe in barium hexaferrite results in a reduction of Curie temperature (T _C) from 730 K known for the parent compound BaFe₁₂O₁₉ to 430 K. Magnetization measurements show that, in BaFe₁₀Sc₂O₁₉, in addition to the magnetic transition at 250 K corresponding to longitudinal conical magnetic structure, another magnetic anomaly occurs in the vicinity of 50 K (T _max). Ac susceptibility and magnetic relaxation show that the magnetic transition at T _max is associated with spin glass like dynamics. Field dependence of this glassy transition temperature follows the Almeida-Thouless (A-T) line expected for spin glass-like behaviour. Unit cell volume obtained from the neutron diffraction (ND) measurements shows deviation from the Debye-Gruneisen behaviour below 50 K, revealing the magnetoelastic coupling. Existence of magnetoelastic coupling is also confirmed by Raman spectra as Raman modes show anomalous changes around 50 K and also indicates presence of lattice modulation. Further, the magnetic structure obtained from ND data shows that incommensurate longitudinal conical ferrimagnetic structure persists from 210 K to 3 K. The integrated intensity of (0 0 2) peak and magnetic moments undergoes a subtle change below 50 K that seems to favour coexistence of long range magnetic ordering and spin glass-like dynamics. Significant magneto-dielectric effect was observed around 50 K. Temperature dependent studies of dielectric constant and pyroelectric current indicate the presence of ferroelectricity even in zero magnetic field. Further, existence of ME coupling below 50 K is confirmed by temperature dependence of pyroelectric current under magnetic fields up to 70 kOe. In short, this work identifies a new magnetic anomaly around 50 K, which is spin-glass-like inducing magnetoelastic and ME anomalies, even in the absence of external magnetic fields.

Unveiling spin-glass transition and antiferromagnetic order by μSR studies in spin-chain Sm2BaNiO5

We report the zero-field and longitudinal field muon spin relaxation studies in a spin-chain compound Sm₂BaNiO₅. Two magnetic transitions, that have not been previously detected by the heat capacity and magnetization measurements, are confirmed at 46 and 9 K. The antiferromagnetic order is suggested at 46 K. Analysis of the muon spin polarization unveils the spin-glass transition at 9 K. Time-field scaling relation of the muon spin polarization verifies the spin-spin autocorrelation function following the cut-off power law, which is approximated by the Ogielski form, as employed numerically for characterizing the spin-glasses.

Pyrocurrent anomalies and intrinsic magnetodielectric behavior near room temperature in Li2Ni2Mo3O12, a compound with distorted honeycomb and spin-chains

Keeping current interests to identify materials with intrinsic magnetodielectric behaviour near room temperature and with novel pyroelectric current anomalies, we report temperature and magnetic-field dependent behavior of complex dielectric permittivity and pyroelectric current for an oxide, Li₂Ni₂Mo₃O₁₂, containing magnetic ions with (distorted) honey-comb and chain arrangement and ordering magnetically below 8 K. The dielectric data reveal the existence of relaxor ferroelectricity behaviour in the range 160-240 K and there are corresponding Raman mode anomalies as well in this temperature range. Pyrocurrent behavior is also consistent with this interpretation, with the pyrocurrent peak-temperature interestingly correlating with the poling temperature. ⁷Li NMR offer an evidence for crystallographic disorder intrinsic to this compound and we therefore conclude that such a disorder is apparently responsible for the randomness of local electric field leading to relaxor ferroelectric property. Another observation of emphasis is that there is a notable decrease in the dielectric constant with the application of magnetic field to the tune of about -2.4% at 300 K, with the magnitude varying marginally with temperature. Small loss factor values validate the intrinsic behaviour of the magnetodielectric effect at room temperature.

Size reduction-induced chain breaking in Haldane-chain compounds SrNi2-x Mg x V2O8 (x = 0 and 0.1)

We report size reduction-induced chain breaking in the spin-1 Haldane-chain SrNi_2-x Mg _x V₂O₈ (x  =  0 and 0.1) by magnetization and electron spin resonance measurements. For x  =  0.0, the magnetic susceptibility of all samples can be well described by a temperature-independent term, a Curie-Weiss term and a Haldane-gap term. This implies that a reduced sample grain size breaks the long chain and creates a considerable number of S  =  1/2 edge spins, resulting in the enhancement of magnetization and the decrease of Haldane gap in the samples. These edge spins as well as the other paramagnetic ions at grain boundary and surface might be weakly coupled with each other. For the Mg-doped sample with x  =  0.1, there are more S  =  1/2 spins creased in relative to x  =  0.0 because of a combined effect of lattice defects, Mg-doping and reduced size. In addition, the antiferromagnetic resonance of x  =  0.1 is also presented.

Magnetoelectric Coupling, Ferroelectricity, and Magnetic Memory Effect in Double Perovskite La3Ni2NbO9

We observe ferroelectricity in an almost unexplored double perovskite La3Ni2NbO9. Ferroelectricity appears below ∼60 K, which is found to be correlated with the significant magnetostriction. A reasonably large value of spontaneous electric polarization is recorded to be ∼260 μC/m(2) at 10 K for E = 5 kV/cm, which decreases signifi- cantly upon application of a magnetic field (H), suggesting considerable magnetoelectric coupling. The dielectric permittivity is also influenced by H below the ferroelectric transition. The magnetodielectric response scales linearly to the squared magnetization, as described by the Ginzburg-Landau theory. Meticulous studies of static and dynamic features of dc magnetization and frequency dependent ac susceptibility results suggest spin-glass state below 29 K. Intrinsic magnetic memory effect is observed from zero-field cooled magnetization and isothermal remanent magnetization studies, also pointing spin-glass state below 29 K. Appearance of ferroelectricity together with a significant magnetoelectric coupling in absence of conventional long-range magnetic order is promising for searching new magnetoelectric materials.