Pressure effects on the magnetic phase diagram of the CeNMSb2 (NM: Au and Ag): A DFT study

Abstract

We explore the influence of pressure on the magnetic ground state of the heavy-fermion antiferromagnet (ferromagnet) CeAuSb2 (CeAgSb2) using first-principles calculations. The total-energy differences obtained by including the spin-orbit interactions and the on-site Coulomb potential for the Ce-derived 4 f -orbitals are necessary to realize the accurate magnetic ground state of CeNMSb2 (NM: Au and Ag). According to our results, the appearance of a new magnetic phase of CeAuSb2 (CeAgSb2) at the pressure of 2.1 GPa (3.5 GPa) is due to the rotation of the magnetic easy axis from the <001> to the <100> direction. Additionally, our data confirm that CeAgSb2 is antiferromagnetic (AFM) above a critical pressure Pc, and such a tendency is expected for CeAuSb2 and remains to be seen. Through the spin-orbit-coupling Hamiltonian and detailed information on the occupation of individual 4 f -orbitals of the Ce atom obtained by the electronic-structure calculations, we can deduce the rotation of the magnetic easy axis upon the application of pressure. According to the present and previous studies, the differences among the magnetic properties of CeNMSb2 (NM: Cu, Ag and Au) compounds are not due to the different noble metals, but due to the subtle differences in the relative position of Ce atoms and, in turn, different occupations of Ce 4 f -orbitals.