Ferrimagnetic (FiM) alloys as GdFeCo, formed by rare-earth (RE:Gd) and transition-metal (TM:FeCo) sublattices antiferromagnetically coupled, constitute the most promising platform to develop the next generation for ultrafast spintronics devices. These alloys combine the advantages of ferromagnetic and antiferromagnetic materials, and their properties can be easily manipulated by tunning the relative composition of the RE and TM. For instance, except at the magnetization compensation point, they present a finite magnetization which can be detected with the same techniques as done in ferromagnets. At the same time, FiM are almost insensitive to external magnetic fields and their negligible magnetostatic interaction makes them ideal candidates to store information with high density. They have recently raised strong interest owing to their ultrafast magneto-optical switching properties 1, and the possibility to drive series of domain-walls (DWs) with high speed under current pulses due to spin-orbit torques (SOTs) 2.
We have developed an advanced micromagnetic model (mM) to explore both the local all-optical switching (AOS) under ultrashort laser pulses with duration of a few fs, and the subsequent domain and DW dynamics by injection of current pulses along a heavy metal (HM) underneath the FiM. The scheme is shown in Fig. 1(a). Starting with a uniform state where both sublattices are anti-parallel aligned along the z-axis, a laser pulse is applied. A proper selection of the fluence and duration of the laser pulse 3 results in a reversed domain flanked by two homochiral DWs, which are subsequently driven along the FiM strip upon injection of the current pulses along the HM 4. Fig 1(b)-(c) shows an example of the laser-induced writing and current-driven shifting of a sequence magnetic domains (bits). In the talk, we will describe the details of the mM and how it can be used to infer the potential of these FiM/HM stacks to develop DW-based memory devices.
References
1 See for instance T. A. Ostler et al. Nat. Commun. 3, 1666 (2012).
2 L. Caretta et al. Nature Nanotechnology. 13, 1154 (2018).
3 V. Raposo et al. Phys. Rev. B 105, 104432 (2022).
4 E. Martinez at al. J. Magn. Magn. Mater. 491, 165545 (2019).

Fig.1. (a) Scheme of the HM/FiM stack with the laser. (b) Temporal sequence of laser (top) and current (bottom) pulses to write a 01101000 bit sequence. (c) Snapshots of the resulting bit sequence.