Realization of small intrinsic hysteresis with large magnetic entropy change in La_(0.8)Pr_(0.2)(Fe_(0.88)Si_(0.10)Al_(0.02))_(13) by controlling itinerant-electron characteristics

摘要

Tuning of phase-transition characteristics in La(Fe_xSi_(1-x))_(13) was conducted in view of the correlation between microscopic itinerant electron natures and macroscopic thermodynamic (magnetocaloric) quantities. To realize a small hysteresis loss Q_H accompanied by a large magnetic entropy change ΔS_M in La(Fe_xSi_(1-x))_(13), two types of modulation based on itinerant electron characteristics, namely, the Fermi-level shift and the magnetovolume effect were combined by complex partial substitution of Al and Pr. Ab-initio calculations predict the reduction of a transition hysteresis owing to the Fermi-level shift after partial substitution of Al. On the other hand, the chemical pressure arisen from partial substitution of Pr enhances ΔS_M through magnetovolume effect. The selective enhancement of ΔS_M apart from Q_H by the magnetovolume effect is well explained by the phenomenological Landau model. Consequently, ΔS_M of La_(0.8)Pr_(0.2)(Fe_(0.88)Si_(0.10)Al_(0.02))_(13) is -18 J/kg K under a magnetic field change of 0-1.2T, while the maximum value of Q_H becomes 1/6 of that for La(Fe_(0.88)Si_(0.12))_(13).