Magnetic coupling between nonmagnetic ions:Eu3+in EuN and EuP

Abstract

We consider the electronic structure of, and magnetic exchange (spin) interactions between, nominally nonmagnetic ${\mathrm{Eu}}^{3+}$ ions ($4{f}^{6}$, $S=3$, $L=3$, $J=0$) within the context of the rocksalt structure compounds EuN and EuP. Both compounds are ionic (${\mathrm{Eu}}^{3+}$; ${N}^{3\ensuremath{-}}$ and ${P}^{3\ensuremath{-}}$) semimetals similar to isovalent GdN. Treating the spin polarization within the $4f$ shell, and then averaging consistent with the $J=0$ configuration, we estimate semimetallic band overlaps (Eu $5d$ with pnictide $2p$ or $3p$) of $\ensuremath{\sim}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (EuN) and $\ensuremath{\sim}1.0\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (EuP) that increase (become more metallic) with pressure. The calculated bulk modulus is $130\phantom{\rule{0.3em}{0ex}}(86)\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ for EuN (EuP). Exchange (spin-spin) coupling calculated from correlated band theory is small and ferromagnetic in sign for EuN, increasing in magnitude with pressure. Conversely, the exchange coupling is antiferromagnetic in sign for EuP and is larger in magnitude, but decreases with compression. Study of a two-site model with ${\stackrel{P\vec}{S}}_{1}∙{\stackrel{P\vec}{S}}_{2}$ coupling within the $J=0,1$ spaces of each ion illustrates the dependence of the magnetic correlation functions on the model parameters, and indicates that the spin coupling is sufficient to alter the Van Vleck susceptibility. We outline a scenario of a spin-correlation transition in a lattice of $S=3$, $L=3$, $J=0$ nonmagnetic ions.