Interplay of Orbital Degeneracy and Vacancies in Stabilizing Collinear Magnetic Order in Cr$_{1+\delta}$Te$_2$

TL;DR

This study reveals how structural vacancies in Cr$_{1+ ext{ extdelta}}$Te$_2$ influence orbital degeneracy and magnetocrystalline anisotropy, stabilizing a collinear magnetic order in a layered ferromagnet.

Contribution

It demonstrates that vacancies induce local symmetry breaking, which modifies orbital degeneracy and stabilizes collinear magnetic order in Cr$_{1+ ext{ extdelta}}$Te$_2$.

Findings

Vacancies cause local symmetry breaking and increase orbital degeneracy.

Neutron diffraction confirms collinear spin alignment.

Vacancy-induced changes in magnetocrystalline anisotropy stabilize magnetic order.

Abstract

Cr$_{1+\delta}$Te$_2$, a two-dimensional van der Waals ferromagnet, displays a contested magnetic structure, poised between collinear and non-collinear spin configurations. In this work, we investigate the magnetic structure of Cr$_{1.33}$Te$_2$ at the microscopic level by combining single-crystal neutron diffraction, X-ray absorption spectroscopy, and first-principles calculations. Neutron diffraction measurements reveal a distinct collinear spin alignment, whereas spectroscopic analyses reveal inherent structural vacancies at both Cr and Te sites. These vacancies lead to local symmetry breaking that elevates the orbital degeneracy of the Cr 3$d$ states, as demonstrated by our first-principles analysis. The resulting modification of magnetocrystalline anisotropy emerges as the key mechanism stabilising the collinear magnetic ground state over the non-collinear one in the presence of vacancies. Our findings uncover a vacancy-driven route to control spin anisotropy and magnetic ordering in layered ferromagnets, offering new insights into the design of tunable 2D magnetic materials.