Effect of strain on magnetic and orbital ordering of LaSrCrO$_3$/LaSrMnO$_3$ heterostructures

TL;DR

This study explores how strain influences magnetic and orbital ordering in LaSrCrO$_3$/LaSrMnO$_3$ heterostructures, revealing strain-dependent magnetic moments and orbital occupations that affect their magnetic properties.

Contribution

It provides new insights into strain effects on magnetic and orbital orderings in ultra-thin oxide heterostructures using combined experimental and theoretical methods.

Findings

Magnetic moments are anti-parallel between layers, strain-independent for thin LSMO.

Net ferromagnetic state persists with increasing LSMO thickness.

Strain alters orbital occupation, affecting magnetic interactions.

Abstract

We investigate the effect of strain and film thickness on the orbital and magnetic properties of LaSrCrO$_3$ (LSCO)/LaSrMnO$_3$ (LSMO) heterostructures using bulk magnetometry, soft X-ray magnetic spectroscopy, first-principles density functional theory, high-resolution electron microscopy and X-ray diffraction. We observe an anti-parallel ordering of the magnetic moments between the ferromagnetic LSMO layers and the LSCO spacers leading to a strain-independent ferromagnetic ground state of the LSCO/LSMO heterostructures for LSMO layers as thin as 2 unit cells. As the LSMO thickness is increased, a net ferromagnetic state is maintained, however, the average magnetic moment per Mn is found to be dependent on the magnitude of the substrate-induced strain. The differences in the magnetic responses are related to preferential occupation of the Mn $x^2-y^2$ (in-plane) d-orbitals for tensile strain and $3z^2-r^2$ (out-of-plane) orbitals under compressive strain leading to competing ferromagnetic and anti-ferromagnetic exchange interactions within the LSMO layers. These results underscore the relative contributions of orbital, structural and spin degree of freedom and their tunability in atomically-thin crystalline complex oxide layers.