Fermi level and phase transformations in GdCo$_2$

Abstract

We performed three independent measurements for a polycristalline, ferromagnetic $GdCo_2$ sample in the temperature range from 300-440 K: chemical potential, current flow through the $GdCo_2-polymer-reference$ $% metal$ sandwich and the conventional resistivity mesurement. In all the measurements we observed characteristic temperatures (irregular points) which were confirmed by these methods. It makes an evidence that plenty of transformation processes at heating of the sample take place (here: relative displacements of the $Gd$ and $Co$ ions, grain boundary and domain structure movements, magnetic reordering, etc.). They are not artifacts or experimental error but they rather visualize the fact that heating of a polycristalline material is not a smooth process. All of them clearly demonstrate the behaviour of the chemical potential with changing temperature.