Nano Letters article features new effect in the nascent field of topological spintronics
September 18, 2015 - In the recent Nano Letters article, an interdisciplinary team of physicists, materials scientists and electrical engineers, including Prof. Nikolic and DPA alumni Dr. Farzad Mahfouzi, have demonstrated novel effect in topological-insulator/ferromagnet (TI/FM) heterostructures exposed to microwave radiation.
The fundamental property of newly discovered topological insulator (TI) materials - strong spin-orbit coupling (SOC) which opens an energy gap in the bulk and generates conducting surface electron states robust against backscattering off nonmagnetic disorder - is also of great interest for spintronic applications. For example, recent experiments have demonstrated how injecting conventional unpolarized charge current into TI/FM heterostructures in the direction parallel to the interface can induce magnetization dynamics via spin torque, which could lead to novel memory and logic devices with ultralow power consumption.
In the experiment reported in Nano Letters article, the same TI/FM heterostructures generates charge current in the absence of any dc bias voltage. While it has been known for quite some time that FM layer with precessing magnetization due to microwave absorption pumps pure spin current into adjacent layers, explanation of spin-to-charge conversion by was not well understood due to several competing microscopic mechanisms that rely on either surface of bulk SOC.
The theory developed by Prof. Nikolic and Dr. Mahfouzi makes it possible to disentangle these mechanisms by measuring how generated charge current depends on the cone angle of precessing magnetization. It also predicts giant enhancement of pumped spin current in any system where FM layer is brough into contact with strong interfacial SOC.
The spin pumping, spin-to-charge conversion and spin torque will be major topics at the upcoming workshop on Topological Spintronics & Skyrmionics organized by Prof. Nikolic and colleagues in Grenoble, France.
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ABOUT NANO LETTERS
Nano Letters published by American Chemical Society reports on fundamental research in all branches of the theory and practice of nanoscience and nanotechnology, providing rapid disclosure of the key elements of a study, publishing preliminary, experimental, and theoretical results on the physical, chemical, and biological phenomena, along with processes and applications of structures within the nanoscale range. Out of 69 journals in Nanoscience and Nanotechnology, Nano Letters is #2 in citations and impact factor (13.592 in 2014).