THE MAGNETIC PHASE-TRANSITION IN AMORPHOUS RARE EARTH-TRANSITION METAL-ALLOYS

The magnetic phase transition of amorphous RE-TM alloys is investigate d by measuring the magnetic moment as function of the temperature and the applied field. The samples are produced by both the melt-spinning technique (Fe30Tb70,Fe33Gd67) and the rf-sputtering technique (Fe67Tb3 3, Fe5.16Al15.4Tb33). The critical exponents beta, gamma', gamma and d elta, as well as the reduced critical amplitudes J(0)/J(S)(0), mu h(0) /(k(B)T(c)) and D-0(delta)/h(0) are determined to obtain a complete ov erview on the behavior of the magnetic phase transition. The critical exponents beta, gamma' and gamma are determined by two independent met hods: Modified Arrott plots and the method of scaling plots. As a furt her method for the determination of the critical exponents beta and ga mma, we have used the method of Kouvel and Fisher. The critical expone nt delta is determined from In J versus In(poH) plots. The critical ex ponent values found in general cannot be related definitely to any the oretical prediction, except for Fe30Tb70, for which the critical expon ents agree rather well with the values derived for the three dimension al Heisenberg model. Furthermore, the critical amplitude values show s ignificant deviations from the theoretical values as derived for diffe rent models.