ABSTRACT

NiMnGa-based Heusler alloys are known for their shape-memory effect. However, in this study, the focus will be on the magneto-thermal (magnetocaloric) properties of rapidly solidified Ni₅₀Mn₂₈Ga₂₂ ribbons melt spun at 1300 and 1600 RPM as well as annealed bulk specimens. The ribbons, both as-spun and annealed, and the annealed bulk specimens were tested in a SQUID to determine the magnetic properties at a field of 50 kOe with a temperature step of 3 K in the temperature range 355–385 K. The magnetic data from the isotherms were used to achieve Arrott plots. Second-order transitions were observed in the materials at the T_C temperature. The values of magnetic entropy ΔS_m were calculated from the magnetic data and these were further used to calculate the values of refrigeration capacity RC. The highest RC value of 273 J/kg was obtained for ¹³⁰⁰NMG₅⁸⁰⁰ where 1300, 800 and 5, represent the melt spinning rate in RPM, the annealing temperature in Celsius and the duration of annealing in hours, respectively. The values of ΔS_m were similar for all the ribbons. To confirm the order of the magnetic transition, universal curves were plotted which led to the conclusion that the transformation at the Curie temperature is a second-order ferromagnetic to paramagnetic transition.

摘要

NiMnGa 基 Heusler 合金以其形状记忆效应而闻名。然而，在这项研究中，重点将放在以 1300 和 1600 RPM 熔融纺丝的快速凝固的 Ni ₅₀ Mn ₂₈ Ga ₂₂带以及退火的大块试样的磁热（磁热）性能。在 SQUID 中测试初纺和退火的带材以及退火的大块样品，以确定在 355-385 K 的温度范围内以 3 K 的温度步长在 50 kOe 磁场下的磁性。磁性数据从等温线得到阿罗特图。在T _C温度下在材料中观察到二级转变。磁熵值ΔS _m由磁数据计算得出，并进一步用于计算制冷能力 RC 的值。^对于1300 NMG ₅ ⁸⁰⁰ ，获得了 273 J/kg 的最高 RC 值，其中 1300、800 和 5 分别代表以 RPM 为单位的熔体纺丝速率、以摄氏度为单位的退火温度和以小时为单位的退火持续时间。所有色带的ΔS _m值相似。为了确认磁跃迁的顺序，绘制了通用曲线，得出居里温度下的转变是二阶铁磁到顺磁转变的结论。