Strong Magnetocaloric Coupling in Oxyorthosilicate with Dense Gd³⁺ Spins

Searching for working refrigerant materials is the key element in the design of magnetic cooling devices. Herein, we report on the thermodynamic and magnetocaloric parameters of an X1 phase oxyorthosilicate, Gd2SiO5, by field-dependent static magnetization and specific heat measurements. An overall correlation strength of |J|S2 ≈ 3.4 K is derived via the mean-field estimate, with antiferromagnetic correlations between the ferromagnetically coupled Gd–Gd layers. The magnetic entropy change −ΔSm is quite impressive, reaches 0.40 J K–1 cm–3 (58.5 J K–1 kg–1) at T = 2.7 K, with the largest adiabatic temperature change Tad = 23.2 K for a field change of 8.9 T. At T = 20 K, the lattice entropy SL is small enough compared to the magnetic entropy Sm, Sm/SL = 21.3, which warrants its potential in 2 −20 K cryocoolers with both the Stirling and Carnot cycles. Though with relatively large exchange interactions, the layered A-type spin arrangement ultimately enhances the magnetocaloric coupling, raising the possibilities of designing magnetic refrigerants with a high ratio of cooling capacity to volume

LaMn₃Ni₂Mn₂O₁₂: An A- and B‑Site Ordered Quadruple Perovskite with A‑Site Tuning Orthogonal Spin Ordering

A new oxide, LaMn₃Ni₂Mn₂O₁₂, was prepared by high-pressure and high-temperature synthesis methods. The compound crystallizes in an AA′₃B₂B′₂O₁₂-type A-site and B-site ordered quadruple perovskite structure. The charge combination is confirmed to be LaMn³⁺₃Ni²⁺₂Mn⁴⁺₂O₁₂, where La and Mn³⁺ are 1:3 ordered at the A and A′ sites and the Ni²⁺ and Mn⁴⁺ are also distributed at the B and B′ sites in an orderly fashion in a rocksalt-type manner, respectively. A G-type antiferromagnetic ordering originating from the A′-site Mn³⁺ sublattice is found to occur at <i>T</i>_N ≈ 46 K. Subsequently, the spin coupling between the B-site Ni²⁺ and B′-site Mn⁴⁺ sublattices leads to an orthogonally ordered spin alignment with a net ferromagnetic component near <i>T</i>_C ≈ 34 K. First-principles calculations demonstrate that the A′-site Mn³⁺ spins play a crucial role in determining the spin structure of the B and B′ sites. This LaMn₃Ni₂Mn₂O₁₂ provides a rare example that shows orthogonal spin ordering in the B and B′ sites assisted by ordered A-site magnetic ions in perovskite systems

Charge Transfer Induced Multifunctional Transitions with Sensitive Pressure Manipulation in a Metal–Organic Framework

The metal–organic framework {[Fe­(2,2′-bipyridine)­(CN)₄]₂Co­(4,4′-bipyridine)}·4H₂O (Fe₂Co-MOF) with single-chain magnetism undergoes an intermetallic charge transfer that converts the Fe₂Co charge/spin configurations from Fe³⁺_LS–Co²⁺_HS–Fe³⁺_LS to Fe²⁺_LS–Co³⁺_LS–Fe³⁺_LS (LS = low spin, HS = high spin) around 220 K under ambient pressure. A series of coherent phase transitions in structure, magnetism, permittivity and ferroelectricity are found to take place accompanying with the charge transfer, making Fe₂Co-MOF a unique ferroelectric single-chain magnet at low temperature. Moreover, our detailed measurements of magnetization, dielectric constant, and Raman scattering under high pressures illustrate that the charge transfer as well as the resulting multifunctional transitions can be readily induced to occur at room temperature by applying a tiny external pressure of about 0.5 kbar. The present study thus provides a pressure well-controllable multifunctional material with potential applications in a broad temperature region across room temperature

Pressure Induced Amorphization of Pb²⁺ and Pb⁴⁺ in Perovskite PbFeO₃

Perovskite-type oxides have been the subject of intense research due to their various fascinating physical properties stemming from their charge degree of freedom. PbFeO3 has an unusual Pb2+0.5Pb4+0.5Fe3+O3 charge distribution with a long-ranged ordering of Pb2+ and Pb4+ and two inequivalent Fe3+ sites in a perovskite structure. Combined synchrotron X-ray diffraction and Mössbauer spectroscopy revealed a change to an orthorhombic GdFeO3 structure with a unique Fe3+ site and randomly distributed Pb2+ and Pb4+ at 29.0 GPa, namely, pressure-induced amorphization of Pb2+ and Pb4+. The absence of a charge transfer transition to the Pb2+Fe4+O3 phase, which was expected from the comparison with PbCrO3 and PbCoO3, was verified using ab initio density functional theory calculations in the range of 0–70 GPa

A‑Site and B‑Site Charge Orderings in an <i>s–d</i> Level Controlled Perovskite Oxide PbCoO₃

Perovskite PbCoO₃ synthesized at 12 GPa was found to have an unusual charge distribution of Pb²⁺Pb⁴⁺₃Co²⁺₂Co³⁺₂O₁₂ with charge orderings in both the A and B sites of perovskite ABO₃. Comprehensive studies using density functional theory (DFT) calculation, electron diffraction (ED), synchrotron X-ray diffraction (SXRD), neutron powder diffraction (NPD), hard X-ray photoemission spectroscopy (HAXPES), soft X-ray absorption spectroscopy (XAS), and measurements of specific heat as well as magnetic and electrical properties provide evidence of lead ion and cobalt ion charge ordering leading to Pb²⁺Pb⁴⁺₃Co²⁺₂Co³⁺₂O₁₂ quadruple perovskite structure. It is shown that the average valence distribution of Pb^3.5+Co^2.5+O₃ between Pb³⁺Cr³⁺O₃ and Pb⁴⁺Ni²⁺O₃ can be stabilized by tuning the energy levels of Pb 6<i>s</i> and transition metal 3<i>d</i> orbitals