Crucial role of phase competition and spin-lattice relaxation in gigantic switchable optomagnet effect of (Fe_0.875Zn_0.125)₂Mo₃O₈

It has been discovered that crystal field excitations with spin-flip transition is a key to control switchable optomagnet effects in antiferromagnetic (Fe_0.875Zn_0.125)₂Mo₃O₈. However, when the flipped spins are in excited states to frustrate the balanced spin moments, the photoinduced magnetization has not occurred yet. Only after ultrashort pulses disappears does the gigantic magnetization starts to grow from zero moment. To construct a detailed picture of crystal field excitation, we design the experiment to compare cases between Néel axis perpendicular and parallel to the angular momentum of circularly polarized light. With aids of Kerr effect microscopy and applications of magnetic field, we uncover all indispensable factors for the gigantic optomagnet effect and discern photoinduced switchable magnetization from non-switchable demagnetization. Our experimental designs, while rarely explored, is critical for developments of antiferromagnetic memory devices using insulating oxides.