Magnetic and transport properties of Fe₃(Ga_1-xAl_x)₄ compounds

The magnetic phase transitions of the itinerant-electron system Fe₃(Ga_1−xAl_x)₄, with x in the range 0.00⩽x⩽0.10, are studied by means of magnetisation and (magneto)resistivity measurements. At 65.5 K, with increasing temperature a first-order magnetic phase transition from a ferromagnetic to an antiferromagnetic state is observed for Fe₃Ga₄. Substitution of Al for Ga results in an increase of the transition temperature of 4.1(4) K/at% Al; the low-temperature ferromagnetic state is stabilised with respect to the high-temperature antiferromagnetic state. This behaviour is different to the effect of Co substitution on the Fe sites, where the magnetism is suppressed, eventually leading to paramagnetism. The results are discussed in the framework of the theory on magnetic phase transitions in itinerant-electron systems of Moriya and Usami.