Spin-Orbit Integrated Ground State and Magnetic Anisotropy in Sr$_2$IrO$_4$

TL;DR

This paper develops a microscopic model for Sr$_2$IrO$_4$ that explains its magnetic anisotropy and weak ferromagnetism through the $j_{ ext{eff}}=1/2$ state, highlighting its unique spin-orbital interactions.

Contribution

It introduces a first-principles based $j_{ ext{eff}}$-spin Hamiltonian that accounts for magnetic properties and anisotropy in Sr$_2$IrO$_4$, emphasizing its novel spin-orbital exchange interactions.

Findings

Wannier functions confirm $j_{ ext{eff}}=1/2$ character at the Fermi level.

Effective Hamiltonian explains weak ferromagnetism and anisotropy.

Sr$_2$IrO$_4$ exhibits unique spin-orbital exchange interactions.

Abstract

We present a microscopic model for the anisotropic exchange interactions in Sr$_{2}$IrO$_{4}$. A direct construction of Wannier functions from first-principles calculations proves the $j_{\mathrm{eff}}$=1/2 character of the spin-orbit integrated states at the Fermi level. An effective $j_{\mathrm{eff}}$-spin Hamiltonian explains the observed weak ferromagnetism and anisotropy of antiferromagnetically ordered magnetic state, which arise naturally from the $j_{\mathrm{eff}}$=1/2 state with a rotation of IrO$_{6}$ octahedra. It is suggested that Sr$_{2}$IrO$_{4}$ is a unique class of materials with effective exchange interactions in the spin-orbital Hilbert space.