The magnetic phase transition in amorphous rare earth-transition metal alloys

The magnetic phase transition of amorphous RE-TM alloys is investigated by measuring the magnetic moment as function of the temperature and the applied field. The samples are producedby both the melt-spinning technique (Fe30Tb70, Fe33Gd67) and the rf-sputtering technique (Fe67Tb33, Fe51.6Al15.4Tb33). The critical exponents β, γ ', γ and δ, as well as the reduced critical amplitudes J0/JS(0), μh0/(kBTc) and DJ0μh0 are determine d to obtain a complete overview on the behavior of the magnetic phase transition. The critical exponents β, γ' and γ are determined by two independent methods: Modified Arrot plots and the method of scaling plots. As a further method for the determination of the critical exponents β and γ, we have used the method of Kouvel and Fisher. The critical exponent δ is determined from In J versus In(μ0H) plots. The critical exponent values found in general cannot be related definitely to any theoretical prediction, except for Fe30Tb70, for which the critical exponents agree rather well with the values derived for the three dimensional Heisenberg model. Furthermore, the critical amplitude values show significant deviations from the theoretical values as derived for different models.