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 $T_C$ are possible to take place for an itinerant-electron ferromagnet with a negative mode-mode coupling among spin fluctuations. It is shown that $T_C$ depends strongly on the pressure near the boundary between the first- and second-order transitions. On the other hand, the spontaneous magnetization at $T=0\mathrm{}$ does not depend so much on the pressure. These results are consistent with the observed results for the pyrite compound ${\mathrm{CoS}}_2,$ the Laves phase compound $\mathrm{Lu}(\mathrm{C}\mathrm{o},\mathrm{A}\mathrm{l}{)}_2$ and other ferromagnets which show a metamagnetic transition in the paramagnetic phase.

• Received 8 May 2001

DOI:https://doi.org/10.1103/PhysRevB.65.024413