一级磁结构相变材料Mn0.6Fe0.4NiSi0.5Ge0.5和Ni50Mn34Co2Sn14的磁热效应与磁场的线性相关性

磁熵变（△S_M）与磁场（μ₀H）的相关性已在很多二级相变材料中被研究并报道,但一级相变材料的磁热效应与磁场相关性还少有报道.本文在具有一级磁结构相变的Mn_0.6Fe_0.4NiSi_0.5Ge_0.5材料中研究发现△S_M与μ₀H存在线性相关性,并通过麦克斯韦关系式的数值分析详细讨论了这一线性相关性的来源.同时,进一步发现在低磁场时,△S_M近似正比于μ₀H的平方.该线性相关性同样在一级磁结构相变Ni₅₀Mn₃₄Co₂Sn₁₄材料中得到了印证.但由于一级磁弹相变LaFe_11.7Si_1.3材料相变温度具有更强的磁场依赖性,不具有△S_M的线性相关性,因此,本研究表明,当磁结构相变材料的相变温度具有弱磁场依赖性时,△S_M与μ₀H具有线性相关性.进而,在磁场未达到相变饱和磁场以下,利用△S_M与μ₀H的线性相关性可以有效推测更高磁场下的△S_M.     

Large reversible magnetocaloric effect induced by metamagnetic transition in antiferromagnetic HoNiGa compound

The magnetic properties and magnetocaloric effects(MCE) of Ho Ni Ga compound are investigated systematically.The Ho Ni Ga exhibits a weak antiferromagnetic(AFM) ground state below the Neel temperature TNof 10 K, and the AFM ordering could be converted into ferromagnetic(FM) ordering by external magnetic field. Moreover, the field-induced FM phase exhibits a high saturation magnetic moment and a large change of magnetization around the transition temperature,which then result in a large MCE. A large-?S_M of 22.0 J/kg K and a high RC value of 279 J/kg without magnetic hysteresis are obtained for a magnetic field change of 5 T, which are comparable to or even larger than those of some other magnetic refrigerant materials in the same temperature range. Besides, the μ_0H~(2/3)dependence of |?S_M~(pk)| well follows the linear fitting according to the mean-field approximation, suggesting the nature of second-order FM–PM magnetic transition under high magnetic fields. The large reversible MCE induced by metamagnetic transition suggests that Ho Ni Ga compound could be a promising material for magnetic refrigeration in low temperature range.