Regulation of phase transition and multicaloric effect in magnetocaloric materials

摘要

Solid state refrigeration based on caloric effect has been regarded as an attractive alternative toconventional gas compression technique. Increasing the caloric effect as much as possible is a long-termpursuit. Proper regulation of phase transition by external physical field is an effective means to enhancethe caloric effect. Here we report our recent research progress[1-5]. Large enhancements ofmagnetocaloric effect (MCE) and barocaloric effect (BCE) by hydrostatic pressure have beendemonstrated in La(Fe0.92Co0.08)11.9Si1.1 with second-order transition. First-principles calculationsare performed, which offers a theoretical support for the enlarged caloric effect relative to the evolutionof phase transition nature[1]. Moreover, enhanced lattice entropy change was calculated by Debyeapproximation, and a reliable way to evaluate BCE is demonstrated under a high pressure. Hysteresisloss is a longstanding problem seriously harming refrigeration efficiency. By utilizing nonvolatile straintriggered by a pulse electric field to engineer phase transition process of FeRh film grown on PMN-PTsubstrate, a nonvolatile reduction of hysteresis loss was observed. The application of electric field isavoided during heat absorb/release (magnetization/demagnetization) process, which is helpful to thetechnical design of electric-magnetic dual field refrigeration cycle [2].Moreover, multicaloric and coupled caloric effect driven by hydrostatic pressure and magnetic field hasbeen systematically investigated in Ni-Mn-In [Ref.3] and La(Fe,Si)13-based compounds. Thermodynamicanalysis indicates that the MCE at a certain pressure is equivalent to the MCE at ambient pressureadjusted by the coupled caloric effect. This theoretical result is verified by magnetic measurementsunder various pressures for the both Ni-Mn-In and La(Fe,Si)13-based compounds. Detailed analysisindicates that the coupled caloric effect involving the strengthened magnetostructural coupling underpressure is responsible for the enhanced MCE. The quantitative analysis of cross coupling term driven bydual fields can help to reveal the essence of regulated phase transition and caloric effect by pressure.This work was supported by the National Key Research and Development Program of China, and theNational Natural Sciences Foundation of China.