Direct in situ study of magnetocaloric effect and martensitic twins structure of Ni-Mn-Ga Heusler alloy in high magnetic fields up to 14T.

This work reports the results of the experimental studies of magnetocaloric effect (MCE) in Ni2.16Mn0.84Ga Heusler alloy with separate magnetic and structural phase transitions in adiabatic (ΔT) and quasi isothermal (ΔQ) regimes by direct methods in magnetic fields up to 10 T. The data obtained allow for comparing ΔT and ΔQ values in the vicinity of martensitic transition and Curie point. It is found maximal values of ΔT = 4,7 K at T = 311 K and ΔQ = 4,6 kJ/kg at T = 313 K in the fields H = 10 T. Optical observations of martensitic twins structure origin and evolution under the influence of high magnetic field confirm the reversible magnetic-field-induced martensitic transition at constant temperature T = 313 K in the field 14 T.

本研究报道了通过直接法在最高10特斯拉（Tesla, T）磁场下，对具有分离磁相变与结构相变的Ni₂.₁₆Mn₀.₈₄Ga赫斯勒合金（Heusler alloy）在绝热（ΔT）和准等温（ΔQ）条件下的磁热效应（magnetocaloric effect, MCE）实验研究结果。所得数据可用于比较马氏体转变（martensitic transition）附近及居里点（Curie point）处的ΔT与ΔQ值。研究发现，在H=10 T磁场下，ΔT的最大值为4.7开尔文（Kelvin, K）（对应温度T=311 K），ΔQ的最大值为4.6千焦每千克（kJ/kg）（对应温度T=313 K）。对高磁场作用下马氏体孪晶结构的形成与演化的光学观测证实，在14 T磁场及恒定温度313 K条件下，存在可逆的磁场诱导马氏体转变。