Covalency effects on the magnetism of EuRh2P2

TL;DR

This paper presents a model explaining the unusual Eu valence and high magnetic ordering temperature in EuRh2P2 through covalent bonding to P2 orbitals, contrasting with traditional intermediate valence models.

Contribution

It introduces a covalent hybridization model that accounts for Eu valence and magnetic properties without suppressing ordering temperatures, unlike hybridization with conduction electrons.

Findings

The model predicts tetragonal anisotropy of Curie constants.

It explains the coexistence of non-integral Eu valence and high Neel temperature.

Parameters can be determined from experimental valence and Curie constants.

Abstract

In experiments, the ternary Eu pnictide EuRh2P2 shows an unusual coexistence of a non-integral Eu valence of about 2.2 and a rather high Neel temperature of 50 K. In this paper, we present a model which explains the non-integral Eu valence via covalent bonding of the Eu 4f-orbitals to P2 molecular orbitals. In contrast to intermediate valence models where the hybridization with delocalized conduction band electrons is known to suppress magnetic ordering temperatures to at most a few Kelvin, covalent hybridization to the localized P2 orbitals avoids this suppression. Using perturbation theory we calculate the valence, the high temperature susceptibility, the Eu single-ion anisotropy and the superexchange couplings of nearest and next-nearest neighbouring Eu ions. The model predicts a tetragonal anisotropy of the Curie constants. We suggest an experimental investigation of this anisotropy using single crystals. From experimental values of the valence and the two Curie constants, the three free parameters of our model can be determined.