Negative Zero-Field-Cooled Magnetization in YMn0.5Cr0.5O3 due to Giant Coercivity and Trapped Field

Interfacial negative magnetization in Ni encapsulated layer-tunable nested MoS2 nanostructure with robust memory applications

Combining interfacial interactions and layer-number tunability, the evolution of magnetism in low-dimensional diamagnetic systems like MoS2 is indeed an interesting area of research. To explore this, Ni nanophases with an average size of 12 nm were encapsulated in MoS2 and the magnetization dynamics were studied over the temperature range of 2-300 K. Surprisingly, the newly formed hybrid nanostructure was found to have a negative magnetization state with giant exchange bias that showed a reversible temperature-induced increase in both spin magnetic moment and coercivity. Density functional theory calculations proved an interfacial charge transfer interaction with a spin-polarized density of states. The magnetization state, along with giant exchange correlation among the magnetic clusters, suggested the possibility of robust thermomagnetic memory. The dc magnetization and relaxation, investigated with different measurement protocols, unveiled robust thermoremanent magnetization as a memory effect. The time-dependent magnetization study indicated that contributions from the negative magnetization state along with charge transfer induced spin states are responsible for the memory effect, which can be controlled by both temperature and external field.

Weak ferromagnetic insulator with huge coercivity in monoclinic double perovskite La2CuIrO6

Insulating ferromagnets with high T _C are required for many new magnetic devices. More complexity arises when strongly correlated 3d ions coexist with strongly spin-orbit coupled 5d ones in a double perovskite. Here, we perform the structural, magnetic, and density functional theory (DFT) study of such double perovskite La₂CuIrO₆. A new P2₁/n polymorph is found according to the comprehensive analysis of x-ray, Raman scattering and phonon spectrum. The magnetization reveals a weak ferromagnetic (FM) transition at T _C  =  62 K and short range FM order in higher temperature range. A huge coercivity is found as high as H _C ~ 11.96 kOe at 10 K, which, in combination with the negative trapped field, results in the magnetization reversal in the zero field cooling measurement. The first principle calculations confirm the observed FM state and suggest La₂CuIrO₆ of this polymorph is a Mott insulating ferromagnet assisted by the spin-orbit coupling.

High-Pressure Synthesis, Structures, and Properties of Trivalent A-Site-Ordered Quadruple Perovskites RMn7O12 (R = Sm, Eu, Gd, and Tb)

A-site-ordered quadruple perovskites RMn₇O₁₂ with R = Sm, Eu, Gd, and Tb were synthesized at high pressure and high temperature (6 GPa and ∼1570 K), and their structural, magnetic, and dielectric properties are reported. They crystallize in space group I2/ m at room temperature. All four compounds exhibit a high-temperature phase transition to the cubic Im3̅ structure at ∼664 K (Sm), 663 K (Eu), 657 K (Gd), and 630 K (Tb). They all show one magnetic transition at T_N1 ≈ 82-87 K at zero magnetic field, but additional magnetic transitions below T_N2 ≈ 12 K were observed in SmMn₇O₁₂ and EuMn₇O₁₂ at high magnetic fields. Very weak kinklike dielectric anomalies were observed at T_N1 in all compounds. We also observed pyroelectric current peaks near 14 K and frequency-dependent sharp steps in dielectric constant (near 18-35 K)-these anomalies are probably caused by dielectric relaxation, and they are not related to any ferroelectric transitions. TbMn₇O₁₂ shows signs of nonstoichiometry expressed as (Tb_{1- x}Mn _x)Mn₇O₁₂, and these samples exhibit negative magnetization or magnetization reversal effects of an extrinsic origin on zero-field-cooled curves in intermediate temperature ranges. The crystal structures of SmMn₇O₁₂ and EuMn₇O₁₂ were refined from neutron powder diffraction data at 100 K, and the crystal structures of GdMn₇O₁₂ and (Tb_0.88Mn_0.12)Mn₇O₁₂ were studied by synchrotron X-ray powder diffraction at 295 K.