Davide Bossini
The wildly growing field of antiferromagnetic spintronics mainly deals with single-domain states materials, even if generating this configuration requires magnetic fields available only in a handful of dedicated facilities in the world. Optical experiments are usually performed focussing the beams into a single domain, whose size can be increased in several materials by annealing. Domains are thus perceived as a nuisance, occurring in the ground state of antiferromagnets, to be avoided for an efficient control of spins. In my talk paper I will discuss recent results, which experimentally disprove this commonly accepted wisdom. Relying on a spectroscopic opto-magnetic investigation of the femtosecond spin dynamics in the archetypal antiferromagnet NiO in a multidomain state I will demonstrate: i) the excitation and a novel mechanism to arbitrary amplify a THz magnon mode via the exciton-magnon transition[1]; ii) nonlinear femtosecond spin dynamics, in the form of coupling between the different magnon modes, typically orthogonal in a single-domain state; iii) the microscopic nature of the coupling between modes, which is due to the presence of domain walls. This last point was supported by a phenomenological model[2] and, most importantly, by means of a control experiment performed in a single domain of the material. This experiment confirms that the coupling between the modes requires domain walls, as it is not observed in a single domain[3].
[1] Nat. Phys.14, 370 (2018)[2] J. Phys. D: Appl. Phys. 54, 374004 (2021)
[3] Physical Review Letters 127, 077202 (2021)