Magnetic phase transitions in (Fe1-xTx)(3)Ga-4 alloys

The magnetic ordering in the series of transition metal alloys (Fe1-xTx)(3) Ga-4 with T = Ni and Ti having values of x in the range 0.05 less than or e qual to x less than or equal to 0.20 has been investigated at high fields a nd low temperatures. Magnetization measurements revealed that in contrast t o other T substitutions, Ni and Ti induce completely different types of eff ects on the magnetic properties. In the case of Ni substitution a ferrimagn etic-like type of magnetic order is induced at low compositions and low tem peratures and Ti produces a ferromagnetic ground state. For Ti alloys with low composition as the temperature is increased a field induced transition starts to appear at about 50 K which persists up to room temperature sugges ting a phase transition from a ferromagnetic to an antiferromagnetic state. The phase diagrams of the Ni and Ti system are explainable in terms of the Moriya-Usami and Isoda theories. Preliminary neutron diffraction measureme nts on the Ni alloys carried out at ILL suggest the existence of short-rang e order over a certain temperature range. The behavior observed so far on t he various substituted systems leads us to believe that there is a clear re lation between the magnetic properties and the relative position of the sub stitution element with respect to Fe in the Periodic Table. (C) 2000 Americ an Institute of Physics. [S0021-8979(00)29908-8].