Itinerant-electron metamagnetism and the onset of ferromagnetism in Laves phase compounds

Detailed magnetization measurements have been carried out for Laves phase compounds which have a C15-type structure up to x = 0.220. A clear increase in the lattice constant occurs at room temperature in the vicinity of x = 0.095, corresponding to the critical concentration of the onset of ferromagnetism. A representative first-order metamagnetic transition was observed in the compounds with x = 0.090 and 0.093 in relatively low fields below 9 T. The critical temperature from the first- to second-order metamagnetic transition in both compounds and the susceptibility maximum temperature for several paramagnetic compounds were obtained. It should be noted that practically coincides with for x = 0.093, very close to the critical concentration of the onset of ferromagnetism. This result is well explained by the recent theory associated with spin fluctuations. The temperature shifts to lower temperatures with increasing x and disappears at x = 0.095 and above, correlated with the onset of ferromagnetism also. The spontaneous magnetization per Co atom exhibits a maximum value of at x = 0.110, whereas the Curie temperature does not show a maximum value at the same composition.