Emergence of transient domain wall skyrmions after ultrafast demagnetization

Abstract

It is known that ultrafast laser pulses can be used to deterministically switch magnetization and create skyrmions; however, the deterministic creation of a single Néel skyrmion after ultrafast demagnetization remains an open question. Here we show domain wall skyrmions also emerge in systems with broken inversion symmetry after exposure to an ultrafast laser pulse, carrying an integer topological charge. While domain wall skyrmions do not appear in the relaxed state due to quick thermal decay following an Arrhenius law, they play a key role in controlling the final skyrmion population through annihilations with skyrmions of opposite topological charge, with the resultant skyrmion states following a Poisson distribution. Using single-shot linearly polarized laser pulses, as well as a train of circularly polarized laser pulses, we show that when a high degree of disorder is created, the possibility of nucleating a single Néel skyrmion is accompanied by the possibility of nucleating a skyrmion with domain wall skyrmion pair, which results in a self-annihilation collapse.

Boris computational spintronics—High performance multi-mesh magnetic and spin transport modeling software

“…84 The mean number of skyrmions formed is dependent on the laser power and follows a Poisson counting distribution as discussed in Ref. 85. Two examples are shown in Fig.…”

Micromagnetic Monte Carlo method with variable magnetization length based on the Landau–Lifshitz–Bloch equation for computation of large-scale thermodynamic equilibrium states

“…[35], with 300 nm width, reaching a maximum of 400 K at the centre, from 300 K at the extremities. Such non-uniform temperature profiles are encountered in ultrafast laser-induced skyrmion nucleation studies [34][35][36][37]. Whilst the MMC method evidently does not reproduce the dynamics, it may be used to analyse the states resulting on a long time-scale, such as mixed labyrinth domain and skyrmion states.…”

“…Finally we also compute the hysteresis loop with a non-uniform temperature profile, in particular a Gaussian temperature profile as in Ref. [35], with 300 nm width, reaching a maximum of 400 K at the centre, from 300 K at the extremities. Such non-uniform temperature profiles are encountered in ultrafast laser-induced skyrmion nucleation studies [34][35][36][37].…”

Non-equilibrium heating path for the laser-induced nucleation of metastable skyrmion lattices

“…This is different from modelling results of Refs. 25,26 where skyrmions were a ground state created due to a phase transition from ferromagnetic to the paramagnetic state and consequent cooling in which case there is no necessity for specific ultrafast non-equilibrium excitation. Note that at zero temperatures the difference between the skyrmion and the stripe domain energies in the simulated system of 55 nm × 55 nm is 0.33 × 10 −18 J, the skyrmionic configuration being more energetic.…”