Pressure dependence of the ferromagnetic to antiferromagnetic transition in Fe-3(Ga1-xAlx)(4) with x = 0.0 and 0.1

The ferromagnetic to antiferromagnetic transition in Fe3Ga4 is studied by m eans of ac-susceptibility measurements under chemical and external hydrosta tic pressure. Substitution of Al for Ga results in an increase of the ferro magnetic to antiferromagnetic transition temperature (T-0) of 4.1(4) K/at. % Al. Application of hydrostatic pressures up to 7 kbar also yields a posit ive effect: dT(0)/dp 53.4(4)K/kbar. The external-pressure-induced increase of T-0 in Fe-3(Ga0.9Al0.1)(4) is considerably weaker: dT(0)/dp=0.93(10) K/k bar. Thermal-expansion measurements reveal that the volume change at the fe rromagnetic to antiferromagnetic transition Delta V/V amounts to only 0.02% . We believe that the volume effect in conjunction with a shift in the Ferm i level drives the ferromagnetic to antiferromagnetic transition. The detai ls of the band structure at the Fermi surface determine the magnetic proper ties and may give rise to the strong pressure dependence of T-0. (C) 1999 A merican Institute of Physics. [S0021-8979(99)57408-2].