Thin film quantum materials

Abstract:

Magnetic skyrmions are localized swirls of magnetization with a nontrivial topological winding number. This winding increases their robustness to superparamagnetism and gives rise to a myriad of novel dynamical properties, making them attractive as next-generation information carriers. Recently the equation of motion for a skyrmion was derived using the approach pioneered by Thiele, allowing for macroscopic skyrmion systems to be modeled efficiently. This powerful technique suffers from the prerequisite that one must have a priori knowledge of the functional form of the interaction between a skyrmion and all other magnetic structures in its environment. Here we attempt to alleviate this problem by providing a simple analytic expression that can generate arbitrary repulsive interaction potentials from the micromagnetic Hamiltonian, using it to provide a correction to the interaction between a skyrmion and the boundary of its material. We also discuss a toy model of the radial profile of a skyrmion, which is accurate for a wide range of material parameters.

Abstract:

The technique of x-ray detected ferromagnetic resonance (XFMR) represents an indispensable new tool in the investigation of spin current effects in complex heterostructures, as it enables the observation of magnetization and spin dynamics with element-, site-, and valence state-specificity. Here we give an overview of the development of XFMR and characterize different approaches to measure spin dynamics using synchrotron radiation. We provide a detailed description of the working principle of the technique and give an overview of recent work carried out at beamline 4.0.2 of the Advanced Light Source and beamline I10 of the Diamond Light Source using XFMR. Results from our latest publications demonstrate the capabilities and sensitivity of the technique. Element- and phase-resolution provide intriguing insights into the mechanisms of spin current propagation in multilayers, while the high sensitivity of XFMR allows for detection of even miniscule signals. Most recently, the utilization of linearly polarized x-rays for XFMR and the detection of XFMR by means of x-ray diffraction rather than x-ray absorption demonstrate two new capabilities in the investigation of spin dynamics.

Abstract:

Engineering the anomalous Hall effect (AHE) in the emerging magnetic topological insulators (MTIs) has great potentials for quantum information processing and spintronics applications. In this letter, we synthesize the epitaxial Bi2Te3/MnTe magnetic heterostructures and observe pronounced AHE signals from both layers combined together. The evolution of the resulting hybrid AHE intensity with the top Bi2Te3 layer thickness manifests the presence of an intrinsic ferromagnetic phase induced by the topological surface states at the heterolayer-interface. More importantly, by doping the Bi2Te3 layer with Sb, we are able to manipulate the sign of the Berry phase-associated AHE component. Our results demonstrate the un-paralleled advantages of MTI heterostructures over magnetically doped TI counterparts, in which the tunability of the AHE response can be greatly enhanced. This in turn unveils a new avenue for MTI heterostructure-based multifunctional applications.