Influence of palladium on the unidirectional anisotropy field in NiMn disordered systems

Abstract

Abstract We have carried out AC susceptibility, hysteresis cycle and torque measurements on (Ni 76− x Pd x )Mn 24 , with 0 ⩽ x ⩽ 5, bulk alloys in the temperature and field ranges of 4.2–260 K and 0–20 kG, respectively. The AC susceptibility curves, χ ′( T ), present a maximum at the same freezing temperature, T g , as the isoelectronic alloy Ni 76 Mn 24 . These alloys exhibit also the same Curie temperature, T c , and the same saturated magnetization, M s . However, both the unidirectional anisotropy field, H a , and the coercivity field, H c , increase considerably with the palladium content. For instance, H a is 1.5 times larger for (Ni 74 Pd 2 )Mn 24 than for Ni 76 Mn 24 . The torque measurements give approximately the same H a at 4.2 K as the hysteresis cycle. We conclude that Pd impurities enhance unidirectional anisotropy but have practically no effect on T c , T g and M s . This is ascribed to the greater spin-orbit coupling of palladium.