Spin-orbit coupling control of anisotropy, ground state and frustration in 5d2 Sr2MgOsO6

TL;DR

This study investigates how spin-orbit coupling influences magnetic properties, anisotropy, and frustration in the 5d2 compound Sr2MgOsO6, revealing high-temperature antiferromagnetic order and reduced magnetic moments.

Contribution

It provides the first quantitative measurement of magnetic moments in a 5d2 system and demonstrates SOC's role in determining ground state and relieving frustration.

Findings

Sr2MgOsO6 orders antiferromagnetically at 108 K

Magnetic moment is significantly reduced to 0.60 muB

SOC induces anisotropy and influences magnetic ground state

Abstract

The influence of spin-orbit coupling (SOC) on the physical properties of the 5d2 system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d2 system of 0.60(2) muB - a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the size of the local moment in this compound. Through comparison to Sr2ScOsO6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d2 systems relative to their 5d3 counterparts, providing an explanation of the high TN found in Sr2MgOsO6.