Giant multiple caloric effects in charge transition ferrimagnet

磁場と圧力でマルチに冷却可能な酸化物新材料 --フェリ磁性電荷転移酸化物におけるマルチ熱量効果の実証--. 京都大学プレスリリース. 2021-06-22.Caloric effects of solids can provide us with innovative refrigeration systems more efficient and environment-friendly than the widely-used conventional vapor-compression cooling systems. Exploring novel caloric materials is challenging but critically important in developing future technologies. Here we discovered that the quadruple perovskite structure ferrimagnet BiCu₃Cr₄O₁₂ shows large multiple caloric effects at the first-order charge transition occurring around 190 K. Large latent heat and the corresponding isothermal entropy change, 28.2 J K⁻¹ kg⁻¹, can be utilized by applying both magnetic fields (a magnetocaloric effect) and pressure (a barocaloric effect). Adiabatic temperature changes reach 3.9 K for the 50 kOe magnetic field and 4.8 K for the 4.9 kbar pressure, and thus highly efficient thermal controls are achieved in multiple ways

Relation between paramagnetic entropy and disordered local moment in La(Fe0.88Si0.12)13 magnetocaloric compound

The paramagnetic fluctuations are investigated in La(Fe0.88Si0.12)13. The disordered local moment (DLM) is represented by the first principle calculations. With a reduction of the volume, the DLM amplitude decreases gradually. In the temperature dependence of electrical resistivity ρ under hydrostatic pressure, an upturn in the variation of ρ in the paramagnetic state was observed with decreasing temperature, which is originated from the Curie-Weiss-type DLM fluctuations. In the vicinity of the critical pressure for disappearance of the DLM, the variation of ρ as a function of log(T) was observed

Concentration Dependence of Pressure Effect in La(Fe x Si 1Àx ) 13 Compounds

Effects of pressure P on the magnetic moment M and the Curie temperature T C have been investigated for La(Fe x Si 1Àx ) 13 above and below the magnetic phase boundary concentration x ¼ 0:86, where the ferromagnetic-paramagnetic transition at T C changes from the first-order (x ! 0:86) to the second-order (x < 0:86). The pressure coefficient of M exhibits a sluggish variation against concentration and no anomaly was observed at x ¼ 0:86, being consistent with the Landau expansion model. On the other hand, T C for the second-order transition has a large negative pressure coefficient dT C =dP and its magnitude increases with increasing x. Above x ¼ 0:86, the magnitude of dT C =dP for the first-order transition increases with x, contrary to the theoretical expectation. It has been revealed that the spin-wave dispersion coefficient becomes smaller when the first-order transition becomes clear by changing the concentration and also applying pressure. Consequently, it is plausible that dT C =dP above x ¼ 0:86 is enhanced by the increase of instability of the ferromagnetic state