Understanding antiferromagnetic spin-orbit heterostructures with a single-spin microscope

Cornell University, Ithaca NY

Investigators

Abstract

Nontechnical Summary This research seeks to understand and control a class of magnetic materials, antiferromagnets, that are abundant in nature but produce no macroscopic magnetic fields. In these materials, the atomic-scale sources of magnetism alternate directions and thus fully cancel when observed from a distance. Until recently, these materials have played little role in magnetic science and technology, with the principle application being the modification of other magnetic materials. However, the potential for antiferromagnetic materials as active elements that store and process information has emerged. Their advantages, including ultra-fast dynamics and insensitivity to applied magnetic fields, make them attractive for high-performance information storage. The research team’s approach acknowledges the critical role of material interfaces for advanced magnetic memory technologies. Additionally, this project addresses a key challenge in this field – that antiferromagnetic materials are difficult to study because they produce no magnetic fields except at atomic-scale distances from the sample. The team is tackling this challenge using an atom-scale quantum sensor scanned in nanoscale proximity to antiferromagnetic materials and their interfaces, thus enabling the measurement of otherwise undetectable magnetic fields at the smallest length scales. Training for graduate and undergraduate students contributes to a workforce with convergent knowledge in materials physics and quantum information technology. Additionally, this project provides hands-on science educational opportunities aimed at elementary school students that encourage positive relationships with role models and contributes to a scientifically literate society. Technical Summary This project examines interfaces between antiferromagnetic materials and materials with strong spin-orbit coupling with the main question: can spin-orbit coupling modify AF spin order? For example, the research team is examining the potential formation of an interfacial Dzyaloshinskii-Moriya interaction (or antisymmetric exchange) that induces chiral spin order and modifications to antiferromagnetic anisotropy at an interface. This project also seeks to understand how uncompensated magnetic moments, which are critical to the interfacial magnetism in antiferromagnet/ferromagnet heterostructures, contribute in the case of antiferromagnet/spin-orbit coupling interfaces. The magnetic materials that the research team work with include antiferromagnets such as nickel oxide, chromia, iridium manganese, iron rhodium and others, as well as ferrimagnets near compensation such as rare earth alloys and garnets, which enable temperature and compositional tuning of the net magnetization. The materials with strong spin-orbit coupling include heavy metals (Pt, Ta, W, Ir) and topological insulators (bismuth selenide and related materials). To understand spin order in these heterostructures, the research team must overcome the experimental difficulties associated with study of antiferromagnetic materials – the lack of an average magnetization that can be detected using conventional techniques. This project takes advantage of the exquisite sensitivity and spatial resolution that is possible using a scanning-probe nitrogen-vacancy center magnetic microscope. The team is using this quantum-enhanced sensor to detect the tiny magnetic fields at surfaces and interfaces, and they are developing new approaches designed for antiferromagnetic material imaging including coherence imaging, relaxometry, and image reconstruction. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.