Physics & Astronomy Colloquium: Dr. Changmin Lee, Lawrence Berkeley National Laboratory


Location: 127 Nieuwland Science Hall

Exploring the dynamics of magnetic order and its excitations using magneto-optics

Dr. Changmin Lee
Postdoctoral Scholar
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 Fe3Sn2. 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