INFLUENCE OF PALLADIUM ON THE UNIDIRECTIONAL ANISOTROPY-FIELD IN NIMNDISORDERED-SYSTEMS

We have carried out AC susceptibility, hysteresis cycle and torque mea surements on (Ni76-xPdx)Mn-24, with 0 less than or equal to x less tha n or equal to 5, bulk alloys in the temperature and field ranges of 4. 2-260 K and 0-20 kG, respectively, The AC susceptibility curves, chi'( T), present a maximum at the same freezing temperature, T-g, as the is oelectronic alloy Ni76Mn24. These alloys exhibit also the same Curie t emperature, T-c, and the same saturated magnetization, M-s. However, b oth 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 (Ni74Pd2)Mn-24 than for Ni76Mn24. The tor que measurements give approximately the same H-a at 42 K as the hyster esis cycle. We conclude that Pd impurities enhance unidirectional anis otropy but have practically no effect on T-c, T-g and M-s. This is asc ribed to the greater spin-orbit coupling of palladium.