Magnetic Coupling Between Non-Magnetic Ions: Eu3+ in EuN and EuP

TL;DR

This study investigates the electronic structure and magnetic interactions of nominally nonmagnetic Eu^3+ ions in EuN and EuP, revealing pressure-dependent exchange couplings and potential spin-correlation transitions in these semimetallic compounds.

Contribution

It provides the first detailed analysis of magnetic exchange interactions between Eu^3+ ions in EuN and EuP, highlighting how these interactions vary with pressure and influence magnetic properties.

Findings

EuN exhibits ferromagnetic exchange coupling increasing with pressure.

EuP shows antiferromagnetic exchange coupling decreasing with pressure.

Pressure affects the semimetallic band overlaps and magnetic interactions.

Abstract

We consider the electronic structure of, and magnetic exchange (spin) interactions between, nominally nonmagnetic Eu^3+ ions (4f^6, S=3, L=3, J=0) within the context of the rocksalt structure compounds EuN and EuP. Both compounds are ionic [Eu^3+; N^3- and P^3-] 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 ~0.1 eV (EuN) and ~1.0 eV (EuP) that increase (become more metallic) with pressure. The calculated bulk modulus is 130 (86) 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 S_1*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.