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Open AccessArticle

Forced Magnetostrictions and Magnetizations of Ni2+xMnGa1−x at Its Curie Temperature

Department of Mechanical and System Engineering, Faculty of Science and Technology, Ryukoku University, Otsu, Shiga 520-2194, Japan
Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan
Kurume Institute of Technology, Kurume, Fukuoka 830-0052, Japan
Center for Advanced High Magnetic Field Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
Research Institute for Engineering and Technology, Tohoku Gakuin University, Tagajo, Miyagi 985-8537, Japan
Author to whom correspondence should be addressed.
Materials 2018, 11(11), 2115;
Received: 16 September 2018 / Revised: 21 October 2018 / Accepted: 25 October 2018 / Published: 28 October 2018
(This article belongs to the Special Issue Fundamental Science and Applications of Highly Functional Alloys)
Experimental investigations into the field dependence of magnetization and the relationship between magnetization and magnetostriction in Ni2+xMnGa1−x (x = 0.00, 0.02, 0.04) alloy ferromagnets were performed following the self-consistent renormalization (SCR) spin fluctuation theory of itinerant ferromagnetism. In this study, we investigated the magnetization of and magnetostriction on Ni2+xMnGa1−x (x = 0.02, 0.04) to check whether these relations held when the ratio of Ni to Ga and, the valence electron concentration per atom, e/a were varied. When the ratio of Ni to Ga was varied, e/a increased with increasing x. The magnetization results for x = 0.02 (e/a = 7.535) and 0.04 (e/a = 7.570) suggest that the critical index δ of HMδ is around 5.0 at the Curie temperature TC, which is the critical temperature of the ferromagnetic–paramagnetic transition. This result confirms Takahashi’s spin fluctuation theory and the experimental results of Ni2MnGa. The spontaneous magnetization pS slightly decreased with increasing x. For x = 0.00, the spin fluctuation parameter in k-space (momentum space; TA) and that in energy space (T0) were obtained. The relationship between peff/pS and TC/T0 can also be explained by Takahashi’s theory, where peff indicates the effective magnetic moments. We created a generalized Rhodes-Wohlfarth plot of peff/pS versus TC/T0 for other ferromagnets. The plot indicates that the relationship between peff/pS and T0/TC follows Takahashi’s theory. We also measured the magnetostriction for Ni2+xMnGa1−x (x = 0.02, 0.04). As a result, at TC, the plot of the magnetostriction (ΔL/L) versus M4 shows proportionality and crosses the origin. These magnetization and magnetostriction results were analyzed in terms of Takahashi’s SCR spin fluctuation theory. We investigated the magnetostriction at the premartensite phase, which is the precursor state to the martensitic transition. In Ni2MnGa system alloys, the maximum value of magnetostriction is almost proportional to the e/a. View Full-Text
Keywords: ferromagnetic Heusler alloy; magnetization; magnetostriction; itinerant electron magnetism; premartensite phase ferromagnetic Heusler alloy; magnetization; magnetostriction; itinerant electron magnetism; premartensite phase
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Sakon, T.; Hayashi, Y.; Li, D.; Honda, F.; Oomi, G.; Narumi, Y.; Hagiwara, M.; Kanomata, T.; Eto, T. Forced Magnetostrictions and Magnetizations of Ni2+xMnGa1−x at Its Curie Temperature. Materials 2018, 11, 2115.

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