Characterizing and Overcoming Surface Paramagnetism in Magnetoelectric Antiferromagnets

Abstract

We use a combination of density functional theory and Monte Carlo calculations to calculate the surface magnetization in magnetoelectric $\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_3$ at finite temperatures. Such antiferromagnets, lacking both inversion and time-reversal symmetries, are required by symmetry to posses an uncompensated magnetization density on particular surface terminations. Here, we first show that the uppermost layer of magnetic moments on the $(001)$ surface remain paramagnetic at the bulk Néel temperature, bringing the theoretical estimate of surface magnetization density in line with experiment. We demonstrate that the lower surface ordering temperature compared to bulk is a generic feature of surface magnetization when the termination reduces the effective Heisenberg coupling. We then propose two methods by which the surface magnetization in $\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_3$ could be stabilised at higher temperatures. Specifically, we show that the effective coupling of surface magnetic ions can be drastically increased either by a different choice of surface Miller plane, or by $\mathrm{Fe}$ doping. Our findings provide an improved understanding of surface magnetization properties in AFMs.

Supplementary material included as appendix

References in corpus (10)

• Robust isothermal electric switching of interface magnetization: A route to voltage-controlled spintronics
• Equilibrium magnetization at the boundary of a magnetoelectric antiferromagnet
• Magnetism of chromia
• Surface magnetic ordering in topological insulators with bulk magnetic dopants
• Nanoscale mechanics of antiferromagnetic domain walls
• Co-existence of Bloch and Neel walls in a collinear antiferromagnet
• Magnetic octupole tensor decomposition and second-order magnetoelectric effect
• Local and nonlocal spin Seebeck effect in lateral Pt-$\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_3$-Pt devices at low temperatures
• Analogy between the magnetic dipole moment at the surface of a magnetoelectric and the electric charge at the surface of a ferroelectric
• Microscopic origin of the structural phase transitions at the Cr2O3 (0001) surface

Cited by in corpus (3)

• Surface Magnetization in Antiferromagnets: Classification, example materials, and relation to magnetoelectric responses
• On the sign of the linear magnetoelectric coefficient in Cr${}_2$O${}_3$
• Surface-symmetry-driven Dzyaloshinskii--Moriya interaction and canted ferrimagnetism in collinear magnetoelectric antiferromagnet Cr${}_2$O${}_3$