Sakon Takuo, Hayashi Yuhi, Fukuya Akihito, Li Dexin, Honda Fuminori, Umetsu Rie Y, Xu Xiao, Oomi Gendo, Kanomata Takeshi, Eto Tetsujiro
Department of Mechanical and Systems Engineering, Faculty of Science and Technology, Ryukoku University, Otsu, Shiga 520⁻2194, Japan.
Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311⁻1313, Japan.
Materials (Basel). 2019 Feb 14;12(4):575. doi: 10.3390/ma12040575.
Experimental investigations into the field dependence of magnetization and temperature dependences of magnetic susceptibility in NiMnGa ( = 0.00, 0.02, 0.04) and Co₂VGa Heusler alloy ferromagnets were performed following the spin fluctuation theory of itinerant ferromagnetism, called as "Takahashi theory". We investigated the magnetic field dependence of magnetization at the Curie temperature , which is the critical temperature of the ferromagnetic⁻paramagnetic transition, and also at = 5 K, which concerns the ground state of the ferromagnetic state. The field dependence of the magnetization was analyzed by means of the vs. ⁵ dependence, and the field dependence of the ground state at 5 K was investigated by means of an Arrott plot ( vs. ²) according to the Takahashi theory. As for NiMnGa, the spin fluctuation parameter in -space (momentum space, ) and that in energy space (₀) obtained at and 5 K were almost the same. On the contrary, as for Co₂VGa, the vs. ⁵ dependence was not shown at . We obtained and ₀ by means of an Arrott plot at 5 K. We created a generalized Rhodes⁻Wohlfarth plot of / versus /₀ for the other ferromagnets. The plot indicated that the relationship between / and ₀/ followed Takahashi's theory. We also discussed the spontaneous magnetic moment at the ground state, , which was obtained by an Arrott plot at 5 K and the high temperature magnetic moment, , at the paramagnetic phase. As for the localized ferromagnet, the / was 1. As for weak ferromagnets, the / was larger than 1. In contrast, the / was smaller than 1 by many Heusler alloys. This is a unique property of Heusler ferromagnets. Half-metallic ferromagnets of Co₂VGa and Co₂MnGa were in accordance with the generalized Rhodes⁻Wohlfarth plot with a around 1.4. The magnetic properties of the itinerant electron of these two alloys appeared in the majority bands and was confirmed by Takahashi's theory.
按照巡游铁磁性的自旋涨落理论（即“高桥理论”），对NiMnGa（ = 0.00、0.02、0.04）和Co₂VGa休斯勒合金铁磁体的磁化强度的场依赖性以及磁化率的温度依赖性进行了实验研究。我们研究了居里温度 （铁磁 - 顺磁转变的临界温度）以及5 K时（涉及铁磁态的基态）磁化强度的磁场依赖性。通过 与 ⁵ 的依赖关系分析了磁化强度的场依赖性，并根据高桥理论通过阿罗特图（ 与 ²）研究了5 K时基态的场依赖性。对于NiMnGa，在 和5 K时获得的 - 空间（动量空间， ）和能量空间（₀）中的自旋涨落参数几乎相同。相反，对于Co₂VGa，在 时未显示 与 ⁵ 的依赖关系。我们通过5 K时的阿罗特图获得了 和₀。我们为其他铁磁体创建了 / 与 /₀的广义罗兹 - 沃尔法思图。该图表明 / 与 ₀/ 之间的关系遵循高桥理论。我们还讨论了通过5 K时的阿罗特图获得的基态自发磁矩 以及顺磁相的高温磁矩 。对于局域铁磁体， / 为1。对于弱铁磁体， / 大于1。相比之下，许多休斯勒合金的 / 小于1。这是休斯勒铁磁体的独特性质。Co₂VGa和Co₂MnGa的半金属铁磁体符合广义罗兹 - 沃尔法思图， 约为1.4。这两种合金巡游电子的磁性出现在多数能带中，并得到了高桥理论的证实。
