Exploring the dynamics of magnetic order and its excitations using magneto-optics
Dr. Changmin Lee
Lawrence Berkeley National Laboratory
Harnessing spin degrees of freedom in magnetically ordered systems is one of the central goals of condensed matter physics. Toward this objective, I will describe dynamic magneto-optic experiments that provide novel perspectives toward understanding and controlling the complexities of magnetic systems.
In the first example, I will show spatially-resolved ac Kerr effect microscopy measurements that identify the “hidden” phase that coexists with ferromagnetism in Co3Sn2S2, a material widely considered to be a topological Weyl semimetal. I will demonstrate that the crossover to this “hidden” phase is a manifestation of a 2D phase transition that occurs within the domain wall, in which the magnetization texture changes from continuous rotation to unidirectional variation.
In the second example, I will show time-resolved optical measurements of spin wavepacket propagation in the Kagome ferromagnet FeSn I will demonstrate that spin information can travel significantly faster than the group velocity of ballistic wavepackets as a consequence of the interaction of light with the magnetostatic modes in Fe3Sn2. Effects related to this unusual spin wave “precursor” may have far-reaching consequences toward realizing long-range, ultrafast spin wave transport in both ferromagnetic and antiferromagnetic systems.
Bio: Changmin Lee is a postdoctoral scholar working in the group of Prof. Joe Orenstein at UC Berkeley and Lawrence Berkeley National Laboratory. He started at Berkeley in 2018 following a Ph.D. work at MIT with Prof. Nuh Gedik. Changmin's current research is focused on ultrafast optical investigation of spin wave transport in magnetically ordered systems. Along with a variety of polarization microscopy setups aimed at imaging magnetic textures, he recently developed a time-resolved magneto-optic Kerr effect (tr-MOKE) microscopy that enables optical excitation and detection of propagating spin waves
Hosted by Prof. Assaf