Since the first all-optical switching experiments carried on GdFeCo ferrimagnet 1-2, the all-optical switching represents an ultrafast and easy method to manipulate magnetization without any applied field. Single pulse helicity independent all-optical switching (HI-AOS) has been demonstrated in ferrimagnetic GdFeCo alloy, Gd/FM bilayers where FM is a ferromagnet, and recently in a ferrimagnetic Heusler alloy and Tb/Co multilayer-based electrode 2-5.
In this work, we demonstrate that robust toggle HI-AOS has been observed in ferrimagnetic Tb based multilayers (Fig.1a). The properties of single pulse HI-AOS in Tb-based multilayers mainly differ in two ways compared to GdFeCo alloys. First, the shape of the state diagram of Tb-based multilayers in which the toggle switching can be observed at a pulse duration of 10 ps is completely different from that of GdFeCo alloy 6. The threshold switching fluence (Fswitch) is independent of the laser pulse duration of at least up to 10 ps (Fig. 1b). Moreover, the multidomain fluence (Fmulti), above which a multidomain state is observed in the center of the spot, increases slightly for pulse durations below 3 ps and then remains constant for longer pulse durations. This indicates that the mechanisms responsible for the Tb-based multilayers switching differ from those of Gd-based alloys. Second, the observed equilibrium state after the first laser pulse excitation shows a complex structure with rings of opposite magnetization directions when the fluence increases. This ring structure was observed in all Tb-based multilayer films we have studied so far. The number and the size of the rings depend on the sample composition (thickness of the Tb and transition metal layers) as well as on the annealing condition.
Acknowledgments: UFO, COMRAD
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