First-principles study of the electronic and magnetic properties of cubic GdCu compound

TL;DR

This study uses first-principles calculations to explore the electronic and magnetic properties of cubic GdCu, revealing its antiferromagnetic ground state and estimating its Néel temperature consistent with experiments.

Contribution

It provides a detailed theoretical analysis of GdCu's magnetic structure, transition temperature, and $4f$ electron behavior using advanced DFT+$U$ and RPA methods, addressing experimental observations.

Findings

GdCu exhibits a C-type antiferromagnetic order with a specific spin spiral vector.

The estimated Néel temperature aligns well with experimental data.

The study highlights the sensitivity of $4f$ level shifts to lattice parameters and computational methods.

Abstract

The structural, electronic, and magnetic properties of bulk GdCu (CsCl-type) are investigated using spin density functional theory, where highly localized $4f$ orbitals are treated within LDA+$U$ and GGA+$U$ methods. The calculated magnetic ground state of GdCu using collinear as well as spin spiral calculations exhibits a C-type antiferromagnetic configuration representing a spin spiral propagation vector $\mathbf{Q}=\frac{2\pi}{a}(\frac{1}{2},\frac{1}{2},0)$. The parameters of the effective Heisenberg Hamiltonian are evaluated from a self-consistent electronic structure and are used to determine the magnetic transition temperature. The estimated N\'{e}el temperature of the cubic GdCu using GGA+$U$ and LDA+$U$ density functionals within the mean field and random phase approximations are in good agreement with the experimentally measured values. In particular, the theoretical understanding of the experimentally observed core Gd $4f$ levels shifting in photoemission spectroscopy experiments is investigated in detail. By employing the self-consistent constrained random-phase approximation we determined the strength of the effective Coulomb interaction (Hubbard $U$) between localized $4f$ electrons. We find that, the shift of Gd-$4f$ states in GdCu with respect to bulk Gd within DFT+$U$ is sensitive to choice of lattice parameter. The calculations for $4f$-level shifts using DFT+$U$ methods as well as Hubbard-1 approximation are not consistent with the experimental findings.