Curie temperature of METGLAS magnetic alloys measured by different techniques

A series of experiments was performed to determine the Curie temperature T
c
of six METGLAS® magnetic alloys using three different techniques: thermogravimetry with magnetic field, differential scanning calorimetry (DSC), and magnetic susceptibility. The purpose of the work was to assess the sensitivity of the three methods, to establish the relationships between magnetic properties and enthalpy in the vicinity of T
c
, and finally, to determine physically valid criteria for T
c
when using the susceptibility method. The full matrix of data is given for the following METGLAS alloys: 2605S-2, 2605SC, 2605S-3A, 2705M, 2826MB, and 2605CO. Good accord between the temperature-dependence of magnetic moment, susceptibility, and enthalpy of the first five alloys is shown. A feature which can be identified with T
c
is defined for each of the measurement methods. Interesting behavior was observed in the case of the METGLAS alloy 2605CO which has so small an enthalpy of the magnetic transition that DSC cannot be used. Both magnetic methods used, thermogravimetry with magnetic field and susceptibility, reveal a steplike temperature-dependence of magnetic moment and susceptibility. A strong dependence of T
c
on the heating rate during measurement was observed, indicating superposition of the magnetic disordering and relaxation processes in the amorphous state. Extrapolation of the data shows that the virtual T
c
for METGLAS 2605CO in the completely amorphous state should be as high as 547°C (820 K).