Giant multiple caloric effects in charge transition ferrimagnet

Abstract

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.

Giant caloric effects in charge–spin–lattice coupled transition-metal oxides

“…3a), which is synthesized by a solid–state reaction under high-pressure (9 GPa) and high-temperature (1000 °C) conditions, contains the unusually high-valence Cr 3.75+ ions at the B site. 31,49 In contrast to the intersite charge transfer transition in NdCu 3 Fe 4 O 12 , the compound shows charge disproportionation transition of Cr 3.75+ to Cr 3+ and Cr 4+ (4Cr 3.75+ → Cu 3+ + 3Cr 4+ ) at 190 K to relieve its electronic instability. The high-temperature Bi 3+ Cu 3 2+ Cr 4 3.75+ O 12 phase thus changes to the low-temperature Bi 3+ Cu 3 2+ Cr 3+ Cr 3 4+ O 12 phase, and the first-order-type transitions in electronic transport, magnetic, and lattice properties are observed, as respectively shown in Fig.…”

“…Interesting examples were recently found in oxide materials containing unusually high-valencestate transition-metal ions. 30,31 A phase transition was primarily induced by relieving the electronic instability of the unusually high valence state of the constituent transition-metal ion, and drastic changes in electronic, magnetic, and structural properties ocurred concomitantly. Significant latent heat associated with phase transition was observed, and more importantly, the observed large latent heat was accessed by applying external fields.…”

Novel functional properties of charge-transition oxides synthesized under high pressure

“…The behavior is completely different from those observed in normal second-order magnetic transitions induced by usual magnetic interactions between the constituent spins. 33),50), 51) The projected magnetic transition temperature extrapolated from the fitting with a Brillouin function to the temperature dependent refined magnetic moment is 643 K, which is much higher than the actual magnetic transition temperature induced by the intermetallic-chargetransfer-transition occurring near room temperature. Given a simple orderdisorder magnetic transition model of the S = 5/2 (Fe 3+ ) spins, the magnetic entropy change is expected to be RIn(2S + 1) = 79 J K ¹1 kg ¹1 .…”

Thermal properties and phase transition behaviors of possible caloric materials Bi0.95Ln0.05NiO3

“…A similar large entropy change induced by the charge-disproportionation transition was also found in BiCu 3 Cr 4 O 12 , where a latent heat of 5.23 kJ kg −1 can be utilized by applying both magnetic elds and pressure. 15 In the caloric effects of NdCu 3 Fe 4 O 12 and BiCu 3 Cr 4 -O 12 , the charge transitions induced unusual rst-order magnetic transitions, and large changes in the magnetic entropies were abruptly yielded at the charge-transition temperatures. 16 These results aroused interest in exploring novel transitionmetal oxides showing charge-transfer transitions for solid caloric materials.…”