Argonne National Laboratory

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Fundamentals of Spintronic Energy Harvesting and Skyrmionic Devices

Materials Science Seminar
Giovanni Finocchio, University of Messina, Italy
July 13, 2018 11:00AM to 12:00PM
Building 241, Room D172

Abstract: In this talk, I will discuss our recent results in the field of spintronic energy harvesting and magnetic skyrmion achieved in collaboration with experimental partners. Electromagnetic energy harvesting technologies offer an attractive energy source for applications in self‐powered portable electronics in the "Internet of things" era. Here we show the development of a bias‐field‐free nanoscale spintronic diode (NSD) based on a magnetic tunnel junction (MTJ) having a canted magnetization in the free layer, and we demonstrate that this NSD could be an efficient harvester of broadband ambient RF radiation, capable of efficiently harvesting microwave powers of microwatt and below. We have measured the rectified voltage with an radio-frequency (RF) current in the absence of an applied magnetic field by applying an RF current to the device through a bias tee by using a signal generator, while the rectification voltage VDC across the MTJ is recorded with a nanovoltmeter. The frequency response of the NSD shows that a novel type of frequency behavior (i.e., broadband response) is achieved.

Magnetic skyrmions are topological protected solitons with a chirality that can be stabilized by the Dzyaloshinskii‐Moriya interaction (DMI). Understanding the physical properties of magnetic skyrmions is important for fundamental research with the aim of developing new spintronic device paradigms where both logic and memory can be integrated at the same level or for unconventional computing. We have recently studied different mechanisms of stabilization of skyrmions in confined devices:one that needs a large DMI to introduce in the energy landscape an energetic minimum associated with a metastable skyrmion state and one that gives a skyrmion state whose size depends on a trade-off among magnetostatic, exchange, and DMI energies. In this seminar, we will show a universal model based on the micromagnetic formalism combining a proper ansatz and scaling relationships and a specific Q‐d phase space (quality factor Q vs. reduced DMI d) that can be used to study skyrmion stability as a function of magnetic field and temperature.