Coupled ferroelectric polarization and magnetization in spinel FeCr2S4

2D Air-Stable Nonlayered Ferrimagnetic FeCr2S4 Crystals Synthesized via Chemical Vapor Deposition

The discovery of intrinsic 2D magnetic materials has opened up new opportunities for exploring magnetic properties at atomic layer thicknesses, presenting potential applications in spintronic devices. Here a new 2D ferrimagnetic crystal of nonlayered FeCr2S4 is synthesized with high phase purity using chemical vapor deposition. The obtained 2D FeCr2S4 exhibits perpendicular magnetic anisotropy, as evidenced by the out-of-plane/in-plane Hall effect and anisotropic magnetoresistance. Theoretical calculations further elucidate that the observed magnetic anisotropy can be attributed to its surface termination structure. By combining temperature-dependent magneto-transport and polarized Raman spectroscopy characterizations, it is discovered that both the measured Curie temperature and the critical temperature at which a low energy magnon peak disappeared remains constant, regardless of its thickness. Magnetic force microscopy measurements show the flipping process of magnetic domains. The exceptional air-stability of the 2D FeCr2S4 is also confirmed via Raman spectroscopy and Hall hysteresis loops. The robust anisotropic ferrimagnetism, the thickness-independent of Curie temperature, coupled with excellent air-stability, make 2D FeCr2S4 crystals highly attractive for future spintronic devices.

Sequence of superconducting states in field cooled FeCr2S4

In the present article we discuss theoretically the emergence of superconductivity in field cooled FeCr₂S₄. The chromium electrons form a triplett_2gstates and due to antiferromagnetic exchange with the iron spins have Zeeman splitting. Applied, during preparation, magnetic field along the moment of iron ions, successively compensates the Zeeman splittings. The chromium electrons with zero Zeeman energy form Cooper pairs induced by iron magnons. In that way, we predict theoretically the existence of sequence of superconducting states in field cooled FeCr₂S₄. Actually there are three different superconductors prepared applying, during preparation, different magnetic fields. In these compounds superconductivity coexist with the saturated magnetism of iron ions.

Mechanochemical Synthesis and Magnetic Characterization of Nanosized Cubic Spinel FeCr2S4 Particles

Nanosized samples of the cubic thiospinel FeCr2S4 were synthesized by ball milling of FeS and Cr2S3 precursors followed by a distinct temperature treatment between 500 and 800 °C. Depending on the applied temperature, volume weighted mean (L vol) particle sizes of 56 nm (500 °C), 86 nm (600 °C), and 123 nm (800 °C) were obtained. All samples show a transition into the ferrimagnetic state at a Curie temperature T C of ∼ 167 K only slightly depending on the annealing temperature. Above T C, ferromagnetic spin clusters survive and Curie-Weiss behavior is observed only at T ≫ T C, with T depending on the heat treatments and the external magnetic field applied. Zero-field-cooled and field-cooled magnetic susceptibilities diverge significantly below T C in contrast to what is observed for conventionally solid-state-prepared polycrystalline samples. In the low-temperature region, all samples show a transition into the orbital ordered state at about 9 K, which is more pronounced for the samples heated to higher temperatures. This observation is a clear indication that the cation disorder is very low because a pronounced disorder would suppress this magnetic transition. The unusual magnetic properties of the samples at low temperatures and different external magnetic fields can be clearly related to different factors like structural microstrain and magnetocrystalline anisotropy.

Even and odd crystal fields on Fe2+ions, local lattice distortion parameters, electron-deformation interaction, and magnetoelectric coupling in FeCr2O4

Within the framework of the quantum mechanical approach, the available experimental data are analyzed to identify the electronic structure of the multiferroic FeCr₂O₄. The relative values of the key contributions to the parameters of even and odd crystal fields acting on the 3delectrons of the Fe²⁺ion are determined. Data on local lattice distortions are systematized. The parameter of the electron-deformation interaction of the ground term Fe²⁺(⁵E) is determined considering lattice distortions, and the parameters of binding of the spins of Fe²⁺and Cr³⁺to the electric field are estimated. The calculation results are compared with the available experimental data on the magnetic and structural characteristics of FeCr₂O₄, the critical temperature of the transition to an orbitally ordered state, optical conductivity data, the Mössbauer effect study, and measurements of spontaneous electric polarization.

Constructing Asymmetrical Ni-Centered {NiN2O4} Octahedra in Layered Metal-Organic Structures for Near-Room-Temperature Single-Phase Magnetoelectricity

Layered metal-organic structures (LMOSs) as magnetoelectric (ME) multiferroics have been of great importance for realizing new functional devices in nanoelectronics. Until now, however, achieving such room-temperature and single-phase ME multiferroics in LMOSs have proven challenging due to low transition temperature, poor spontaneous polarization, and weak ME coupling effect. Here, we demonstrate the construction of a LMOS in which four Ni-centered {NiN₂O₄} octahedra form in layer with asymmetric distortions using the coordination bonds between diphenylalanine molecules and transition metal Ni(II). Near room-temperature (283 K) ferroelectricity and ferromagnetism are observed to be both spontaneous and hysteretic. Particularly, the multiferroic LMOS exhibits strong magnetic-field-dependent ME polarization with low-magnetic-field control. The change in ME polarization with increasing applied magnetic field μ₀H from 0 to 2 T decreases linearly from 0.041 to 0.011 μC/cm² at the strongest ME coupling temperature of 251 K. The magnetic domains can be manipulated directly by applied electric field at 283 K. The asymmetrical distortion of Ni-centered octahedron in layer spurs electric polarization and ME effect and reduces spin frustration in the octahedral geometry due to spin-charge-orbital coupling. Our results represent an important step toward the production of room-temperature single-phase organic ME multiferroics.

A new pnictidehalide with van der Waals host–guest interactions exhibiting both geometric spin frustration and resistive humidity sensitivity

The structure and electric and magnetic properties of a new metal pnictidehalide (Hg₆P₄)(CrCl₆)Cl are reported in detail. The weak van der Waals interactions in its structure are responsible for its geometric spin frustration and good resistive humidity sensitivity.