Interplay between Dilution of the U-Sublattice and Pressure in Determining the Magnetic State of UCoAl-Based Materials

UCoAl系物質の磁気状態におけるU副格子希釈と高圧力が及ぼす効果

We have prepared a single crystal of U0.94Y0.06CoAl and studied the field and temperature dependence of magnetization under hydrostatic pressure. Dilution of the U sublattice by Y in the 5f-band metamagnet UCoAl leads to paramagnetism above 15% Y but at low Y content the spontaneous ferromagnetism is stabilized, presumably due to a small lattice expansion and increase of the U-U spacing. The ferromagnetism vanishes at 0.3 GPa and a characteristic S-shape magnetization curve develops under pressure. Temperature dependence of magnetic susceptibility shows reentrance of the metamagnetism under pressure as well.

Joint Lab. for Magnetic Studies (Czech Republic): A.V. Andreev, V. Sechovsky
Institute of Metal Physics (Russia): N.V. Mushnikov
IMR, Tohoku University: K. Koyama, Y. Shiokawa, I. Satoh, K. Watanabe
Reference: To be published in the Journal of Alloys and Compounds.

U0.94Y0.06CoAlの磁化の温度変化と磁場変化を静水圧下において測定した．5fバンドメタ磁性体UCoAlは，UをYで置換したとき15%以下では強磁性が安定となり，それ以上になると常磁性に変化する．これはY置換による格子の膨張に伴うU-U原子間距離の増大によると考える．さらに，強磁性が安定なU0.94Y0.06CoAlに圧力を加えると，0.3GPa以上で強磁性が消失し，再びメタ磁性状態が安定となることが明らかとなった．

Joint Lab. for Magnetic Studies (Czech Republic): A.V. Andreev, V. Sechovsky
Institute of Metal Physics (Russia): N.V. Mushnikov
東北大学金属材料研究所: 小山佳一，塩川佳伸，佐藤伊佐務，渡辺和雄