Using Selective Excitations and Phase Competitions to Control Antiferromagnetic Optomagnets

Yu-Miin Sheu^1*, Y. H. Zhang¹, H. W. Liu¹, Y. M. Chang¹, C. P. Change¹, Y. H. Li¹, T. Kurumaji²

¹Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
²Department of Physics, Mathematics and Astronomy,, California Institute of Technology, California, USA
³Center for Emergent Matter Science (CEMS),, RIKEN, Japan

* Presenter:Yu-Miin Sheu, email:ymsheu@nycu.edu.tw

On-demand spin polarization is crucial for advancing memory devices and spintronics. In this presentation, I demonstrate an optomagnetic effect with switchable magnetization emerging from an initial zero magnetic moment in the polar antiferromagnet (Fe,Zn)2Mo3O8 using a magnetic unit. Gigantic Kerr rotation is observed by exploiting crystal-field excitations and the helicity of ultrashort laser pulses. This effect arises from the intrinsic antiferromagnetic ordering and is further stabilized by the phase competition between antiferromagnetic and ferrimagnetic states. Unlike conventional spin-flip mechanisms that rely heavily on spin-orbit coupling, the spin-flip excitation observed here occurs within the 200 fs laser pulse duration and does not depend on spin-orbit interaction. However, following the laser pulse, spin-lattice relaxation plays a critical role in the continued magnetization growth, which can persist for over 3 ns and lead to a giant optical Kerr effect. Therefore, both phase competition and spin-lattice relaxation are essential for inducing strong optomagnetic responses in antiferromagnets. These mechanisms are further validated through comparative analysis of crystal-field excitations with light propagation vectors k//(100) and k//(001),

Keywords: optomagnet, ultrafast, antiferromagnet, polar, switchable