Enhanced Performance of ΔT_ad upon Frequent Alternating Magnetic Fields in FeRh Alloys by Introducing Second Phases

Abstract

The cyclability and frequency dependence of the adiabatic temperature change (ΔT ad ) under an alternating magnetic field (AMF) are significantly important from the viewpoint of refrigeration application. Our studies demonstrated, by direct measurements, that the cyclability and low-magnetic-field performance of ΔT ad in FeRh alloys can be largely enhanced by introducing second phases. The ΔT ad under a 1.8 T, 0.13 Hz AMF is reduced by 14%, which is much better than that (40−50%) of monophase FeRh previously reported. More importantly, the introduction of second phases enables the antiferromagnetic−ferromagnetic phase transition to be driven by a lower magnetic field. Thus, ΔT ad is significantly enhanced under a 0.62 T, 1 Hz AMF, and its value is 70% larger than that of monophase FeRh previously reported. Although frequency dependence of ΔT ad occurs, the specific cooling power largely increases by 11 times from 0.17 to 1.9 W/g, as the frequency increases from 1 to 18.4 Hz under an AMF of 0.62 T. Our analysis of the phase transition dynamics based on magnetic relaxation measurements indicates that the activation energy barrier is lowered owing to the existence of second phases in FeRh alloys, which should be responsible for the reduction of the driving field. This work provides an effective way to enhance the cyclability and lowmagnetic-field performance of ΔT ad under an AMF in FeRh alloys by introducing second phases.

Phase transition regulation, magnetocaloric effect, and abnormal thermal expansion

“…控, 将PMN-PT衬底上的FeRh薄膜的可用制冷 温区动态拓宽至60 K (327 -387 K) [33] . 在减小滞 后损耗方面, 通过使用-6 kV/cm脉冲电场(诱发 的非易失应变)和磁场双场调控, 使PMN-PT衬 底上的FeRh薄膜整个相变温区(310 -360 K)内 滞后损耗降低了56%左右 [34] ; 并且, 为满足实际制 冷需求进一步研究了FeRh磁热材料的循环稳定 性 [35] . 依据热力学关系, 定量地研究了Ni 50 Mn 35 In 15 合金在静水压和磁场下的耦合热效应, 揭示了压力 通过增强该类材料中磁-结构耦合强度, 导致磁场 驱动的相变过程中熵变增强的规律 [36] .…”

“…我们通过将铁电PMN-PT基片在脉 0 kV/cm applied at 5 T. Supposing the produced strain could be larger, path 6 would be along path 6' or path 6'' instead, and then the enveloped area by path 5-6' or 5-6'' would approach zero or turn out to be inverse. Lower panel, an exploded diagram corresponds to the above processes [34] .…”

“…热效应的循环稳定性(图16(c) -(e)) [35] . 在1.8 T, 0.13 Hz的交变磁场下, ΔT ad 降低14%, 稳定后的 gram of heat flow from FeRh film to the heat transfer medium (Cu) and the PMN-PT substrates [34] . FeRh的ΔT ad (下降40% -50%) [91] (图16(a), (b)).…”

“…15 FeRh层向Cu层和PMN-PT层热传导示意图 (a)以Cu为传热介质时, 有限元模拟得到的Cu层, FeRh层和PMN-PT层的温度随时间的变化结果; (b)热量从FeRh层传导到传热介质(Cu层)和PMN-PT基片层的示意图[34] …”