Speaker:  Prof. Yu-Miin Sheu 
Department of Electrophysics
National Yang Ming Chiao Tung University 
Time：2022/3/22  Tuesday 1:30PM-3:00PM
Place：Lecture room 124, Dept. of Phys. 

Title : Crystal field excitation and double-pulse switching of antiferromagnets

Abstract: 
On-demand spin polarization is essential for memory devices and spintronics. Optomagnet effect, where switchable magnetization can be created from zero magnetic moment, is observed in polar antiferromagnetic (Fe,Zn)2Mo3O8with gigantic Kerr rotation by using crystal-field excitations and helicities of ultrashort laser pulses. [1] This effect is achieved via the antiferromgnetic ordering without the need of spin-orbit coupling that splits crystal field degeneracy, and it is further stabilized by the existence of competition between antiferromagnetic and ferrimagnetic phase competition. Unlike many other spin-flip mechanisms, spin-orbit coupling is not crucial here to induce spin-flip excitation within the pulse excitation of 200 fs. However, after the disappearance of laser pulses, spin-lattice relaxation is mandatory to the following continuous growth of magnetization that can last up to 1 ns and induce gigantic optical Kerr rotation. As a result, both phase competition and spin-lattice relaxation are key ingredients to introduce large optomagnet effects in antiferromagnets. These mechanisms are confirmed from the comparison of crystal field excitation between light propagation k//(001) and k//(100). Finally, I will demonstrate the idea of using double pulses to initiate a nonzero moment and switch the created moment to the opposite direction—all of which occurs in antiferromagnets. 
Reference: 
[1] Sheu, Y. M. et al., Physical Review X 9, 031038 (2019).