Itinerant-electron metamagnetism and strong pressure dependence of the Curie temperature

A temperature dependence of the Landau coefficients for an itinerant-electron metamagnet is discussed on the spin fluctuation model, by taking the magnetovolume effect into account. Both of the first- and second-order transitions at the Curie temperature TC are possible to take place for an itinerant-electron ferromagnet with a negative mode-mode coupling among spin fluctuations. It is shown that TC depends strongly on the pressure near the boundary between the first- and second-order transitions. On the other hand, the spontaneous magnetization at $T=0$ does not depend so much on the pressure. These results are consistent with the observed results for the pyrite compound CoS₂, the Laves phase compound Lu(Co,Al)₂ and other ferromagnets which show a metamagnetic transition in the paramagnetic phase.