Magnetic analysis of a ferromagnetic cluster system in partially ordered Ni3Mn alloy

The magnetization vs. temperature curves for Ni3Mn alloys with long range order parameters, S=0.13 and 0.29 have an inflection point near Curie point T-F. The curves show a ferromagnetic-phase profile in lower temperature and a long tail as a glass-like phase in wide temperature range above T-F. We analyzed the magnetization in the glass-like phase by using of a superferromagnetic model in which a random set of ferromagnetic clusters with intra-and inter-cluster ferromagnetic couplings is taken into account. The method which has been used for magnetic analysis of rapidly quenched La-Fe alloys by Siratori et ol. is found to be adequate to analyze the magnetization in the glass-like phase for a partially ordered Ni3Mn alloy. From these results, it is found that the magnetization in the glass-like phase depends on the average size of the ferromagnetic clusters distributed in nonmagnetic matrix. The cluster for the long range ordered Ni3Mn contains 140-2200 atoms (1.4(3)-2.9(3) nm(3)) and the volume fraction of ordered regions is 0.11-0.32, which increases with S.