Itinerant-electron metamagnetism of the Laves-phase compounds Lu(Co1-xGax)2 under high pressures with high magnetic fields

Magnetic properties of the Laves phase compounds Lu(Co1-xGax)(2) (0.10 less than or equal to x less than or equal to 0.22) have been investigated under the duplicate conditions, i.e., high magnetic fields with high pressures. The pressure effect on the Curie temperature T-C is extremely large in the vicinity of x = 0.10, which is close to the critical concentration for the onset of ferromagnetism. The spontaneous magnetization M-S around x = 0.10 is drastically decreased and a paramagnetic state is induced by applying pressure. The paramagnetic state is changed into a ferromagnetic state by applying magnetic field, accompanied by a metamagnetic transition. The Landau coefficients up to the sixth-order terms of the magnetization for x = 0.10 were estimated from the experimental data. The pressure dependence of the critical transition field H-C for x = 0.10 is consistent with the results calculated from the obtained coefficients. For the compounds with x less than or equal to 0.15, the pressure coefficient of the spontaneous magnetization, partial derivative In M-S / partial derivative P, is much larger than the pressure coefficient of the Curie temperature, partial derivative In T-C / partial derivative P, implying that there is a peak of the density of state just below the Fermi energy. The variation of partial derivative In T-C / partial derivative In M-S as a function of x near the critical concentration of the onset of ferromagnetism can be explained by the theory for itinerant ferromagnets having a negative coefficient b, of the fourth-order term in the Landau expansion. [S0163-1829(99)02413-3].