Abstract
Interfaces between correlated complex oxides are promising avenues to realize new forms of magnetism that arise as a result of charge transfer, proximity effects, and locally broken symmetries. We report on the discovery of a noncollinear magnetic structure in superlattices of the ferromagnetic metallic oxide (LSMO) and the correlated metal (LNO). The exchange interaction between LSMO layers is mediated by the intervening LNO, such that the angle between the magnetization of neighboring LSMO layers varies in an oscillatory manner with the thickness of the LNO layer. The magnetic field, temperature, and spacer thickness dependence of the noncollinear structure are inconsistent with the bilinear and biquadratic interactions that are used to model the magnetic structure in conventional metallic multilayers. A model that couples the LSMO layers to a helical spin state within the LNO fits the observed behavior. We propose that the spin-helix results from the interaction between a spatially varying spin susceptibility within the LNO and interfacial charge transfer that creates localized states. Our work suggests a new approach to engineering noncollinear spin textures in metallic oxide heterostructures.
- Received 16 October 2015
DOI:https://doi.org/10.1103/PhysRevX.6.041038
Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Magnets are typically “collinear,” meaning that the magnetic moments of the electrons that give the material its magnetism are aligned either parallel or antiparallel to each other (i.e., pointing either north or south). As a result, breaking a bar magnet in two results in pieces in which the poles still align along the same direction as in the original magnet. In relatively few materials, however, the magnetization develops a “twist” where neighboring moments are not collinear. Such noncollinear arrangements of spin can give rise to novel properties that may be useful in spintronics applications or in realizing novel superconducting states for quantum computing. However, noncollinear magnetic materials, particularly those that are good electrical conductors, are very rare. Furthermore, their degree of noncollinearity (i.e., the angle in the twist between neighboring magnetic moments) is an intrinsic material property that cannot usually be tailored by design. Here, we discover that when two metallic oxides [ (ferromagnet) and (nonmagnetic)] are stacked together in a multilayer roughly 60 nm thick, they develop a robust noncollinear magnetic structure.
Working at temperatures as low as 10 K, we show that the angle between the magnetization of adjacent layers can be adjusted by varying the thickness of the spacer. This result is surprising since multilayers made of conventional metals such as Fe and Cu typically form collinear magnetic structures. Noncollinear magnetism in conventional multilayers only occurs for a very narrow range of nonmagnetic metal layer thickness and cannot be tuned by design. The explanation for the robust noncollinearity (maximum value: 100 degrees) and its tunability in multilayers may lie in the nature of the nonmagnetic spacer. We find that the spacer becomes magnetic in proximity with the layer, and our theoretical calculations and measurements hint that the twist in magnetization may originate in the magnetic structure of the spacer.
Our study opens a new vista for the design and manipulation of noncollinear magnetic states in engineered nanostructures for possible low-power, high-speed memory and logic applications.