Our recent research article “Proximity-induced anisotropic magnetoresistance in magnetized topological insulators” was featured by Applied Physics Letters.  This article discusses the magnetoresistance in bilayers of topological insulators (Bi2Se3) and ferrimagnetic insulator (Y3Fe5O12; YIG).  We observe that the orientation of the magnetization YIG controls the magnitude of the gap in the electronic band structure of the adjacent topological insulator.

Our PhD student Robin Klause received a ThinkSwiss Scholarship for a research visit to Switzerland.  He will work during the summer of 2021 in the group of Prof. Pietro Gambardella at the ETH Zürich in order to investigate spin-orbit torques in non-collinear antiferromagnetic metals.

Our recent research article on “Distinguishing antiferromagnetic spin sub lattices via the spin Seebeck effect” was featured by Physical Review B as an “Editor’s Suggestion”.  This article discusses how electric voltages generated by temperature gradients across an antiferromagnetic Cr2O3 film enable to get detailed insights into the spin structure of this film.  This provides a new, easy-to-implement method for resolving changes of the magnetic structures of antiferromagnets.

More details can be found here and the full article is available here:
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.103.L020401

The Web of Science has selected Axel Hoffmann as a Highly Cited Researcher in 2020. The list recognizes leading researchers in the sciences and social sciences from around the world. It is based on an analysis of journal article publication and citation data, an objective measure of a researcher’s influence, from 2009-2019.  More details can be found in the Illinois News Feed.

Our recent Perspective article on “Dynamic excitations of chiral magnetic textures” was featured by APL Materials as an “Editor’s Pick”.  This perspective article discusses the different type of dynamic magnetic excitations that occur in chiral magnetic materials with a specific focus on skyrmions.  In particular we also discuss what the experimental hurdles are to observe them, and how these excitations may inform new applications, such as information technologies.

More details can be found here and the full article is available here: https://aip.scitation.org/doi/10.1063/5.0027042 

 

Our recent Perspective article on “Hybrid magnonics: Physics, circuits, and applications for coherent information processing” was featured by the Journal of Applied Physics.  This perspective article focuses on the fundamental physics and device application of hybrid magnon modes, particularly with their potential for coherent information processing.  This build on the recent rapid developments of magnon-based hybrid systems, which seek to combine magnonic excitations with diverse excitations for transformative applications in devices, circuits, and information processing. Key to their promising potentials is that magnons are highly tunable excitations and can be easily engineered to couple with various dynamic media and platforms.

Axel Hoffmann presented a colloquium on “Topological Quasiparticles: Magnetic Skyrmions” via a remote presentation at Case Western University on September 17, 2020.  A recording of this talk is available at by following this link.

Our group received funding from the National Science Foundation to investigate spin-orbit torques with Weyl semimetals for the next three years.  This work will be performed in collaboration with the group from Prof. Steven May from Drexel University.

This grant supports research into understanding new mechanisms by which electrical currents can be used to switch the magnetic orientation of thin magnetic layers in devices for data processing and storage. The use of current pulses to alter magnetism is central to the operating principles of a variety of electronic and spintronic devices. However, new materials systems are needed to reduce the power consumption required for magnetic switching and to enable future device scaling. This award supports fundamental research to identify quantum materials known as Weyl semimetals that enable significant improvements in the efficiency of current-induced magnetic switching. The project will characterize a variety of Weyl semimetals for use in magnetic devices with emphasis on understanding how the switching metrics are influenced by the interfacial properties between the Weyl semimetal and the magnetic layer. The project will also identify how Weyl semimetals can be used to enable switching of perpendicular magnets to facilitate emerging device concepts. The insights into how new quantum materials can reduce power consumption in electronic and magnetic devices may lead to new advances in electronics and computing devices, providing broad societal benefit. The students’ research training enabled by this project will serve to advance the U.S. economic interests by providing them with the experimental skill set needed to contribute to the technological sector.

This collaborative project will lay the groundwork for low-power spintronic devices through a series of research activities aimed at providing a detailed understanding of spin-orbit torques generated by Weyl semimetals. The charge-to-spin conversion process will be thoroughly characterized at a series of interfaces between Weyl semimetals and ferromagnetic metals to quantify torque efficiencies. The interfacial properties of these same structures will be characterized using resonant x-ray reflectivity, a technique that allows for both the elemental concentration and magnetization to be determined as a function of depth across the interfaces. The correlations between spin-orbit torque efficiency and the composition and magnetic properties of the interfaces will elucidate the roles of intrinsic (Weyl physics) and extrinsic (non-idealities at the interfaces) contributions to the torques. These activities will yield a thorough understanding of spin-orbit torques across real interfaces in device-based structures fabricated using industry-relevant deposition processes. The research will also identify novel spin-orbit torques, including those associated with an out-of-plane spin polarization, enabled by the unique properties of Weyl semimetals and quantify torque metrics relevant for non-volatile magnetic memory devices and thermally driven stochastic oscillators, where the magnetization of the free magnetic layer is controlled via spin-orbit torques. Through these research activities, this project will advance progress toward employing Weyl semimetals in emerging electronic and spintronic device architectures.

llinois Materials Science and Engineering Prof. Axel Hoffmann shares about his research on magnetic materials in a seminar for undergraduate students in the Illinois MRSEC REU Program on June 17, 2020. He also discusses careers in National Labs.  You can watch the full presentation here on YouTube.

Our recent Perspective article on “Metallic Antiferromagnets” was featured by the Journal of Applied Physics.  This perspective article focuses on electrical, thermal and optical control and sensing of spins and magnons in metallic antiferromagnets and their potential for revolutionizing the spintronics field.  It thereby highlights some of the main research directions of the Illinois Materials Research Science and Engineering Center (I-MRSEC).