Fermi Level and Phase Transformations in Gdco 2

We observed characteristic temperatures connected with different phase transformations in the polycristalline, ferromagnetic GdCo2 sample possible to appear in the temperature range from 300 K to 440 K. We used here three independent methods applied to still the same GdCo2 sample testing in this way the sensivity of each particular method. One of them was the nonconventional, indirect measurement of the chemical potential as function of temperature. In the second method we measured the current flow through the GdCo2 − polymer − ref erence metal sandwich vs temperature (surface potential barrier method). The first and second methods were applied for the first time to the polycrystalline, magnetic GdCo2 material. The third method was the measurement of the electric resistivity vs temperature. These three independent measurements make an evidence that within the measured temperature range plenty of transformations in the sample take place and that the characteristic temperatures connected with these transformations can be detected with the use of these methods visualizing in this way very important role of 1 the chemical potential in the detection of phase transformations (transitions). The first method (indirect measurement of the chemical potential vs temperature) revealed 24 characteristic temperatures T1 − T24 connected with many different transformation processes within the poly-crystalline, ferromagnetic sample under heating (reorientation, reordering processes, etc.), as well as, the Curie temperature TC (second order phase transition: ferromagnet-paramagnet). With the use of the second method (surface potential barrier method) we could easily identify the characteristic temperatures T8 − T19 and TC in quite good agreement with the first method. The second method revealed also several additional characteristic temperatures which could be seen from appearing peaks in the measured resistivity of the sandwich vs temperature but not seen when using the first method. The application of the third method (the resistiv-ity measurement vs temperature) revealed almost the same values for the characteristic temperatures T1 − T14, T18 − T24 and TC as found with the use of the first method but several, additional characteristic temperatures could also be detected which are not seen when apply the first method and seen with the use of the second one. The existence of characteristic temperatures, confirmed with the use of three independent measurements make an evidence that plenty of transformations (transitions) really take place when heating the polycristalline GdCo2 sample. The applied methods complement each other and can successfully be used to detect characteristic temperatures of …