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

Abstract

The itinerant-electron metamagnetic transition (MT) and the effectsof hydrostatic pressure on the critical transition field BC ofthe MT, on the spontaneous magnetization MS and on the Curietemperature TC have been investigated for well homogenizedLu(Co1-xAlx)2 Laves phase compounds.The critical field BC decreases with increasing x, maintaining alinear relationship with the inverse susceptibility at thetemperature where the susceptibility exhibits a maximum value, χ-1(Tmax). On applying pressure, the magnetization M ofthe ferromagnetic compound with x = 0.100 is drastically decreasedat a critical pressure, resulting in a paramagnetic state. Inaddition, the metamagnetic transition from the paramagnetic to theferromagnetic state is induced by applying an external magnetic field.The effect of pressure on the Curie temperature TC is extremelylarge and negative in the vicinity of the criticalconcentration for the onset of ferromagnetism. The pressurecoefficient of the Curie temperature, ∂ln TC/∂P, is much larger than that of the spontaneous magnetization,∂ln MS/∂P, below x = 0.150. These results canbe explained by the theory for itinerant ferromagnets having anegative coefficient b of the fourth-order term in the Landauexpansion. The Landau expansion coefficients estimated from theexperimental results are in accord with the theories. From theseestimated values, it is concluded that the magneto-volume effectdecreases the critical transition field BC. It has beenconfirmed that the results for Lu(Co1-xAlx)2 are verymuch analogous to those for Lu(Co1-xGax)2.