Confinement of magnetism in atomically thin La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 heterostructures

Abstract

At crystalline interfaces where a valence mismatch exists, electronic and structural interactions may occur to relieve the polar mismatch leading to the stabilization of non-bulklike phases. We show that spontaneous reconstructions at polar La0.7Sr0.3MnO3 interfaces are correlated with suppressed ferromagnetism for film thicknesses on the order of a unit cell. We investigate the structural and magnetic properties of valence-matched La0.7Sr0.3CrO3 -La0.7Sr0.3MnO3 interfaces using a combination of high-resolution electron microscopy, first principles theory, synchrotron X-ray scattering and magnetic spectroscopy and temperature-dependent magnetometry. A combination of an antiferromagnetic coupling between the La0.7Sr0.3CrO3 and La0.7Sr0.3MnO3 layers and a suppression of interfacial polar distortions are found to result in robust long range ferromagnetic ordering for ultra-thin La0.7Sr0.3MnO3. These results underscore the critical importance of interfacial structural and magnetic interactions in the design of devices based on two-dimensional oxide magnetic systems.

Effect of strain on magnetic and orbital ordering of LaSrCrO3/LaSrMnO3 heterostructures

“…For each LSMO thickness, M s is found to be inversely proportional to the magnitude of the substrate-induced strain.For the relatively unstrained heterostructure on LSAT (c/a=1.006), the magnetization increases from 1.3 µ B /M n for N=2 to a value of 3.4 µ B /M n for N=8 close to the expected magnetic moment for bulk LSMO. The increase in the SQUID magnetization with LSMO thickness is related to the reduced contribution to the total magnetization from the LSCO layers with moments anti-aligned to the magnetic field 33. A similar increase is observed for the heterostructures on STO.…”

“…31 For single layer LSMO films, magnetic dead layers are associated with structural, chemical and electronic reconstructions associated with the polar stacking of planes with the LSMO films. 21,26,30,33 Changes to the LSMO octahedra as a result of interfacial structural coupling may also lead changes to the electronic bandwidth of the LSMO films resulting in magnetically dead layers. 31 In the current work, we find that nominally valence-matched and iso-structural LSCO layers are effective in alleviating the interfacial structural and polar mismatch at the LSMO interface leading to the stabilization of a strain-independent FM ground state.…”

“…[29][30][31][32] The insertion of ultrathin La 0.7 Sr 0.3 CrO 3 (LSCO) layers at the interfaces of LSMO films grown on (001)-oriented SrTiO 3 (STO) has been recently found to result in the stabilization of ferromagnetism in LSMO layers as thin as 0.8 nm (2 unit cells (uc)). 33 At these length scales, intrinsic interfacial interactions are expected to dominate the physical properties of the oxide films. Jahn-Teller-like distortions induced by epitaxial strain breaks the degeneracy of the transition metal d -orbitals via the crystal field splitting leading to changes in the electronic occupation of orbitals with in-plane and out-of-plane symmetries.…”

“…For the thinnest LSMO layers (2 uc), the interfacial spin and structural interactions between the LSMO and LSCO layers leads to a net FM ground state characterized by an AF coupling of Mn and Cr spins across the interface. 33,43 LSCO in bulk is a G-type antiferromagnet, 44 however, the interfacial coupling with LSMO leads to a net anti-alignment of the Cr spins with the applied magnetic field. As the LSMO thickness is increased, a net FM state is still maintained, however the effects of epitaxial strain and orbital ordering are non-negligible leading to competing FM and AF exchange interactions within the LSMO layers.…”

High‐Resolution Crystal Truncation Rod Scattering: Application to Ultrathin Layers and Buried Interfaces

“…A survey of recent high‐resolution CTR results using model refinement, direct methods, and hybrid approaches shows that the estimated uncertainty in the relative atomic positions (along the surface normal) is generally less than 0.1 Å (10 pm), the uncertainty in the occupancies is on the order or ≈5–10%, and bond/tilt angles can be determined with a precision a few degrees. [ 1,31,93–100 ]…”