Modulation calorimetry and magnetooptical studies on the magnetic phase transition of liquid Co80Pd20

At the end of the last century by means of the electromagnetic levitation with Co80Pd20 for the first time a liquid could be brought into the neighbourhood of a ferromagnetic phase transition. Albrecht et al. succeeded then 1997 the formation of the magnetic order in a supercooled Co80Pd20 melt. By a new sample stabilization the measurement range has been extended by an important interval. So longer measurement times respectively deeper supercoolings in the neighbourhood of the Curie point are possible. By means of an extended modulation calorimetry both the specific heat capacity cp and the coupling constant κcoup between sample and the alternating field of the levitation coil has been temperature-dependently determined. Thereby for fixed solid samples sharp maxima of the heat capacity at the Curie point resulted. Also the temperature slope of κcoup could be distinctly reduced to the magnetic susceptibility. For the liquid and by this freely floating samples the modulation calorimetry in the present arrangement was proved to be unsufficient. Otherwise than in a solid according to calculations of S. Dietrich and B. Groh in a drop a vortex-shaped domain structure of the ferromagnetic order is to be expected. For the study of this structure a measurement apparatus for the magnetooptical Kerr effect was constructed. By it it is possible to determine the rotation of polarized light at the magnetized surface of the liquid Co80Pd20 samples. By this way conclusions on the forming magnetic structure could be drawn. In the paramagnetic region both a dependence on the applied magnetic field and a distinct temperature dependence of the Kerr angle could be stated. This reflects well the slope of the susceptibility in the same temperature range. In the neighbourhood of the Curie temperature so rotational angles of up to 0.08 were measured