Switching of an Antiferromagnet Controlled by Spin Canting in a Laser-Induced Hidden Phase

During laser-induced phase transitions, fast transformations of electronic, atomic, and spin configurations often involve the emergence of hidden and metastable phases. Being inaccessible under any other stimuli, such phases are indispensable for unveiling mechanisms and controlling the transitions. We experimentally explore spin kinetics during the ultrafast first-order 90° spin-reorientation (SR) transition in a canted antiferromagnet Fe_{3}BO_{6}, and reveal that the transition is controlled by canting between the magnetic sublattices. Laser-induced perturbation of the Dzyaloshinskii-Moriya interaction results in a change of the intersublattice canting within the first picoseconds, bringing Fe_{3}BO_{6} to a hidden phase. Once this phase emerges, laser-induced heating activates precessional 90° spin switching. The combination of spin canting and heating controls the final spin configuration comprising coexisting initial and switched phases. The extended phase coexistence range is in striking contrast to the narrow SR transition in Fe_{3}BO_{6} induced by conventional heating.