Magnetic ground state of ferromagnetic CeAgSb2

Abstract

Abstract We investigated the magnetic easy axis of ferromagnetic CeAgSb2 compound by using the first-principles electronic-structure calculations to clarify the role of 4f electrons. Similar to the case of CeCuSb2 and CeAuSb2 compounds, the total-energy differences and the density of states for Ce 4f electrons show that it is necessary to include both the spin–orbit coupling (SOC) and the so-called LDA+U method in the spin-polarized calculation to predict correct magnetic easy axis for this compound. Especially, we show that the SOC energy calculated by using l · s matrix elements of f-orbitals indicates that the effects of SOC of Ce 4f electrons plays a crucial role to determine the magnetic easy axes of CeNMSb2 (NM: Cu, Ag and Au) compounds. Through the SOC Hamiltonian and detailed information on the occupation of individual f-orbitals of Ce atom obtained by the electronic-structure calculations the correct magnetic easy axis can be deduced. Surprisingly, the two Ce atoms in a unit cell of CeAgSb2 compound should be treated inequivalently, which is similar to the case of antiferromagnetic CeCuSb2 and CeAuSb2 compounds, even though the CeAgSb2 compound is ferromagnetic. The inequivalence of the two Ce atoms is due to the lack of mirror symmetry along the z-axis in this Ce-based compounds.