Ferromagnetism and ferroelectricity in Eu X (X=0, S): pressure effects

摘要

Ferromagnetism and ferroelectricity in Eu monochalcogenides have been investigated by ab initio density functional theory in the DFT vertical bar U approach. Exchange interaction parameters and Curie temperatures under pressure are studied and discussed using Heisenberg Hamiltonian with first and second nearest-neighbor interactions. The calculations showed that the hydrostatic pressure perfectly improves the Curie temperature (EuO: T-C = 175 K; EuS: T-C = 33.8 K) and in the other hand it cannot induce the spontaneous polarization (P-s). The effect of uniaxial and biaxial pressure is also studied. Although the uniaxial strains slightly increases the Curie temperature, it ensures the ferrolectricity in these systems by producing a spontaneous polarization of the order of P-s (EuO) = 57.50 mu C/cm(2) and P-s (EuS) = 42.86 mu C/cm(2) with pressures of 5% and 4%, respectively. The search for new model systems is a necessity to better understand the physics related to multiferrolc materials and to consider possible applications.