Itinerant-electron metamagnetism and magneto-volume effects in Lu(Co1-xAlx)₂Laves phase compounds

The itinerant-electron metamagnetic transition (MT) and the effects of hydrostatic pressure on the critical transition field B C of the MT, on the spontaneous magnetization M S and on the Curie temperature T C have been investigated for well homogenized Lu(Co 1- x Al x ) 2 Laves phase compounds. The critical field B C decreases with increasing x , maintaining a linear relationship with the inverse susceptibility at the temperature where the susceptibility exhibits a maximum value, χ -1 ( T max ). On applying pressure, the magnetization M of the ferromagnetic compound with x = 0.100 is drastically decreased at a critical pressure, resulting in a paramagnetic state. In addition, the metamagnetic transition from the paramagnetic to the ferromagnetic state is induced by applying an external magnetic field. The effect of pressure on the Curie temperature T C is extremely large and negative in the vicinity of the critical concentration for the onset of ferromagnetism. The pressure coefficient of the Curie temperature, ∂ln T C /∂ P , is much larger than that of the spontaneous magnetization, ∂ln M S /∂ P , below x = 0.150. These results can be explained by the theory for itinerant ferromagnets having a negative coefficient b of the fourth-order term in the Landau expansion. The Landau expansion coefficients estimated from the experimental results are in accord with the theories. From these estimated values, it is concluded that the magneto-volume effect decreases the critical transition field B C . It has been confirmed that the results for Lu(Co 1- x Al x ) 2 are very much analogous to those for Lu(Co 1- x Ga x ) 2 .