Abstract
Magnetocaloric materials undergoing reversible phase transitions are highly desirable for magnetic refrig-eration applications.(Mn,Fe)2(P,Si)alloys exhibit a giant magnetocaloric effect accompanied by a magne-toelastic transition,while the noticeable irreversibility causes drastic degradation of the magnetocaloric properties during consecutive cooling cycles.In the present work,we performed a comprehensive study on the magnetoelastic transition of the(Mn,Fe)2(P,Si)alloys by high-resolution transmission electron mi-croscopy,in situ field-and temperature-dependent neutron powder diffraction as well as density func-tional theory calculations(DFT).We found a generalized relationship between the thermal hysteresis and the transition-induced elastic strain energy for the(Mn,Fe)2(P,Si)family.The thermal hysteresis was greatly reduced from 11 to 1 K by a mere 4 at.%substitution of Fe by Mo in the Mn1.15Fe0.80P0.45Si0.55 alloy.This reduction is found to be due to a strong reduction in the transition-induced elastic strain energy.The significantly enhanced reversibility of the magnetoelastic transition leads to a remarkable improvement of the reversible magnetocaloric properties,compared to the parent alloy.Based on the DFT calculations and the neutron diffraction experiments,we also elucidated the underlying mechanism of the tunable transition temperature for the(Mn,Fe)2(P,Si)family,which can essentially be attributed to the strong competition between the covalent bonding and the ferromagnetic exchange coupling.The present work provides not only a new strategy to improve the reversibility of a first-order magnetic transition but also essential insight into the electron-spin-lattice coupling in giant magnetocaloric materials.
基金项目
National Natural Science Foundation of China(51801102)
National Natural Science Foundation of China(U1832191)
National Natural Science Foundation of China(12004179)
National Natural Science Foundation of China(11974184)
Natural Science Foundation of Jiangsu Province(BK20180491)
Natural Science Foundation of Jiangsu Province(BK20180418)
Open Fund of Large Facilities in Nanjing University of Science and Technology()
Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scat-tering Science and Technology()