Magnetic profile of proximity-coupled (Dy,Bi)2Te3/(Cr,Sb)2Te

Abstract

Magnetic topological insulators (TIs) are an ideal playground for the study of novel quantum phenomena building on time-reversal symmetry-broken topological surface states. By combining different magnetic TIs in a heterostructure, their magnetic and electronic properties can be precisely tuned. Recently, we have combined high-moment Dy:Bi 2 Te 3 with high transition temperature Cr:Sb 2 Te 3 in a superlattice, and we found, using x-ray magnetic circular dichroism (XMCD), that long-range magnetic order can be introduced in the Dy:Bi 2 Te 3 layers. Accompanying first-principles calculations indicated that the origin of the long-range magnetic order is a strong antiferromagnetic coupling between Dy and Cr magnetic moments at the interface extending over several layers. However, based on XMCD alone, which is either averaging over the entire thin-film stack or is surface-sensitive, this coupling scenario could not be fully confirmed. Here we use polarized neutron reflectometry, which is ideally suited for the detailed study of superlattices, to retrieve the magnetization in a layer-and interfaceresolved way. We find that the magnetization is, in contrast to similar recent studies, homogeneous throughout the individual layers, with no apparent interfacial effects. This finding demonstrates that heterostructure engineering is a powerful way of controlling the magnetic properties of entire layers, with the effects of coupling reaching beyond the interface region.

Magnetic Structure of Ion-Beam Imprinted Stripe Domains Determined by Neutron Scattering

“…For example, magnetization vector distributions along the surface normal or along the sample plane can be obtained from thin-film systems comprising exchange coupled hard-soft magnetic hybrid materials and phase separation [36,[65][66][67], exchange coupled magnetic multilayers [38,68] and non-magnetic thin film systems [31,37,69]. PNR and OSS can further be used to detect correlations among magnetic domains as a function of depth and laterally in nanoparticle systems or emerging material classes, such as topological insulator [70,71] and multiferroic nanostructures [72].…”

Optimising experimental design in neutron reflectometry

“…An area where it is particularly important to be able to discern small signals and maximise differences between models is in thin film magnetism. It is often the case that small moments are induced by a ferromagnet in neighbouring layers, proximity magnetism [Khaydukov et al, 2013, Duffy et al, 2019, Zhan et al, 2019, Inyang et al, 2019, or where a layer might only have a very small moment in the first place, but the magnitude of this moment is particularly important to know. The advantage of neutrons in these situations is that they provide an absolute moment, so in many ways are the idea tool for the task.…”

Magnetic order in 3D topological insulators—Wishful thinking or gateway to emergent quantum effects?

“…128 This makes Dy-doped TIs a prime candidate for further exploitation in heterostructures, where order can be introduced via proximity coupling. 129,130 Incorporating TIs into magnetic heterostructures has been explored both as an alternative to magnetic doping and as an added materials design opportunity to tune the magnetic properties. Magnetic heterostructures offer the advantage of, e.g., opening an exchange gap in the TI with less disorder than in doped systems since no extra scattering centers need to be introduced.…”

“…128 This makes Dy-doped TIs a prime candidate for further exploitation in heterostructures, where order can be introduced via proximity coupling. 129,130…”

“…128 This makes Dy-doped TIs a prime candidate for further exploitation in heterostructures, where order can be introduced via proximity coupling. 129,130 IV. MAGNETIC HETEROSTRUCTURES In the previous section, we have described how introducing magnetic elements into TIs has been used to achieve magnetically ordered materials.…”