Thermodynamic properties and resistivity of the ferromagnetic semiconductor EuC 2

Abstract

EuC 2 is a ferromagnet with a Curie temperature of T C ≃ 15 K It is semiconducting with the particularity that the resistivity drops by about five orders of magnitude on cooling through T C, which is therefore called a metal-insulator transition. In this paper, we study the magnetization, specific heat, thermal expansion and the resistivity around this ferromagnetic transition on high-quality EuC 2 samples. At T C we observe well-defined anomalies in the specific heat c p(T) and thermal expansion α(T) data. The magnetic contributions of c p(T) and α(T) can satisfactorily be described within a meanfield theory, taking into account the magnetization data. In zero magnetic field, the magnetic contributions of the specific heat and thermal expansion fulfil a Grüneisen scaling, which is not preserved in finite fields. From an estimation of the pressure dependence of T C via Ehrenfest's relation, we expect a considerable increase of T C under applied pressure due to a strong spin-lattice coupling. Furthermore, the influence of weak off-stoichiometries δ in EuC 2±delta; was studied. It is found that δ strongly affects the resistivity, but hardly changes the transition temperature. In all these aspects, the behaviour of EuC 2 strongly resembles that of EuO. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.