On-demand spin orientation with a long polarized lifetime and an easily detectable signal is the ultimate goal for spintronics. However, there still exists a trade-off between controllability and stability of spin polarization, awaiting a significant breakthrough. Here, I will demonstrate switchable optomagnet effects in (Fe1−xZnx)2Mo3O8, from which we can obtain tunable magnetization (spanning from −40% to 40% of a saturated magnetization) that is created from zero magnetization in the antiferromagnetic state without magnetic fields. It is accomplishable by utilizing circularly polarized laser pulses to excite spin-flip transitions in polar antiferromagnets that have no spin canting, traditionally hard to control without very strong magnetic fields. The spin controllability in (Fe1−xZnx)2Mo3O8 originates from its polar structure that breaks the crystal inversion symmetry, allowing distinct on-site d-d transitions for selective spin flip. By chemical doping, we exploit the phase competition between antiferromagnetic and ferrimagnetic states to enhance and stabilize the optomagnet effects, which result in long-lived photoinduced Kerr rotations.[1] Moreover, we discovered that if the ferromagnetic state becomes the ground state by field cooling or by chemical doping, the huge optomagnet effect disappears. This implies that antiferromagnets can be more promising than ferromagnet/ferrimagnet for on-demand spintronics.

Reference:
[1] Y. M. Sheu, Y. M. Chang, C. P. Chang, Y. H. Li, K. R. Babu, G. Y. Guo, T. Kurumaji, and Y. Tokura, Phys. Rev. X, 9, 031038 (2019)