2006-6

Magnetic Properties of MnBi in High Magnetic Field and High Temperature

一次相転移物質MnBiの高温強磁場特性

We have studied the magnetic properties of MnBi in high magnetic fields and high temperature using a Faraday force magnetometer that was developed in HFLSM. The magnetic phase transition temperature (T_t) at B = 0 T is 628 K and linearly increases with increasing magnetic field at the rate of 2.3 KT^-1. A metamagnetic transition between the paramagnetic (Mn_1.08Bi+Bi) and field-induced ferromagnetic (MnBi) states was observed just above T_t. The results obtained suggest that the magnetic, structural, peritectic composition and decomposition can be controlled by magnetic fields.

IMR, Tohoku University : K. Koyama, T. Onogi, K. Watanabe

Reference: T. Onogi, K. Koyama and K. Watanabe,
“Magnetic properties of MnBi in hgh magnetic fields and high temperature”, J. Jpn Inst. Metals 71 (2007) 489-493.
K. Koyama, et al.,
“Magnetic phase transition of MnBi under high magnetic fields and high temperature”, to be published in Mater. Trans.

MnBiは，ゼロ磁場中では628K付近において，強磁性MnBi（NiAs型構造）から常磁性Mn_1.08Bi（Ni₂In型構造）+Bi（液体）に分解を伴って一次相転移をすると報告されている．我々は，強磁場•高温下での磁気特性を解明するために，ファラデー型高温•強磁場磁化測定装置を開発，磁場0-10 T，温度300-773 Kで強磁場磁化測定を行った．その結果，磁場により転移温度は2.3 KT^-1で上昇，さらに626K以上でMnBiのメタ磁性転移の観測にも成功した．これら結果は，MnBiの磁気相転移や結晶構造だけでなく，分解と合成（包晶反応温度）も磁場によって制御できることを示唆している．

東北大学金属材料研究所：小山佳一，小野木哲也，渡辺和雄