Chicago Section

Materials Science Division Seminar

Speaker: Dr. Albert Min Gyu Park

Korea Advanced Institute of Science and Technology (KAIST) 

Abstract:

Topologically non-trivial skyrmion bubbles emerge from a complex energy landscape that involves multiple magnetic energy contributions. Due to their high stability and controllability, this isolated metastable spin texture holds a unique position in applications such as racetracks or logic devices. Most such devices inherit the structure of the skyrmion racetrack memory, which operates in three sequential steps: generation, transportation, and detection of skyrmions. In this talk, I will investigate the unique properties of the generation and transport of skyrmionic bubbles in W/CoFeB/Ta/MgO multilayer using MOKE microscopy.

On the generation of skyrmions, I will demonstrate the role of perpendicular magnetic anisotropy (PMA) by creating an engineered spatial gradient of PMA from the insertion of the Ta wedge layer between CoFeB and MgO. Skyrmion nucleation rates at various temperatures and anisotropy fields are measured and fitted to Arrhenius law to obtain the energy barrier and the attempt time for the skyrmion generation. I will discuss the role of magnetic anisotropy in the Meyer-Neldel-type rule that indicates the entropic effects in the nucleation of skyrmion bubbles in a single-layer thin-film ferromagnet.

While skyrmion speed is often discussed as a central issue for device application, it is also essential to obtain a general principle behind the motion of skyrmions. I will focus on the hopping-like scaling law for skyrmion motion at the creep regime. The statistical method is used to reveal that the motion of the skyrmions at a low drive regime deviates from the typical creep motion expected for magnetic domain walls in 2-dimensional space. The role of structural topology, which is distinguished from the topological charge, will be discussed.

Bio:

Albert Park is a post-doctoral researcher in Prof. Kab-Jin Kim’s group in the Department of Physics at Korea Advanced Institute of Science and Technology (KAIST). He earned his dual bachelor’s degree in physics and electrical engineering and a master’s degree in electrical engineering in 2012 and 2014, respectively, at KAIST. He earned a Ph.D. from the Department of Applied Physics at Cornell University in 2020, where he investigated a wide range of research topics varying from the transport properties of radical polymers to the formation of skyrmions in magnetic multilayers, under the supervision of Prof. Gregory D. Fuchs. His current research focuses on spintronic phenomena involving skyrmions and spin waves.

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