Magnetic proximity effect and shell-ferromagnetism in metastable Ni_(50)Mn_(45)Ga_5

摘要

The present study on magnetic and structural properties of Ni_(50)Mn_(45)Ga_5 confirms that structural metastability is an inherent property of Ni_(50)Mn_(50-x)-X_x: Heusler alloys with X as In, Ga, and Sn. The ternary alloy transforms during temper-annealing into a dual-phase composite alloy. The two phases are identified to be cubic L2_1, Ni_(50)Mn_(25)Ga_(25), and tetragonal Ll_0 Ni_(50)Mn_(50). Depending on the annealing temperature, the magnetic-proximity effect giving rise to shell-ferromagnetism has been observed when annealing is carried out under an external magnetic field. The upper and lower remanence values M_R~+ and M_R~- have the same sign even at high temperatures. Such alloys can be promising candidates for heat- and magnetic-field-resistant magnetic recording media.