Controlling All-Optical Helicity-Dependent Switching in Engineered Rare-Earth Free Synthetic Ferrimagnets.

Jung‐Wei Liao,Liam O'Brien,Victor Raposo,Gregory Malinowski,Unai Atxitia,Michel Hehn,Tarun Vemulkar,Eduardo Martínez,Russell P Cowburn,Pierre Vallobra,Stéphane Mangin,Dorothée Petit

doi:10.1002/advs.201901876

Abstract

All‐optical helicity‐dependent switching in ferromagnetic layers has revealed an unprecedented route to manipulate magnetic configurations by circularly polarized femtosecond laser pulses. In this work, rare‐earth free synthetic ferrimagnetic heterostructures made from two antiferromagnetically exchange coupled ferromagnetic layers are studied. Experimental results, supported by numerical simulations, show that the designed structures enable all‐optical switching which is controlled, not only by light helicity, but also by the relative Curie temperature of each ferromagnetic layer. Indeed, through the antiferromagnetic exchange coupling, the layer with the larger Curie temperature determines the final orientation of the other layer and so the synthetic ferrimagnet. For similar Curie temperatures, helicity‐independent back switching is observed and the final magnetic configuration is solely determined by the initial magnetic state. This demonstration of electrically‐detected, optical control of engineered rare‐earth free heterostructures opens a novel route toward practical opto‐spintronics.

Highlights

To cite this version: Jung-Wei Liao, Pierre Vallobra, Liam O’Brien, Unai Atxitia, Victor Raposo, et al
This demonstration of electrically-detected, optical control of engineered rare-earth free heterouse of circularly polarized optical laser pulses:[1] Spurred by the first observation of all-optical switching (AOS) in rare earth (RE)-transition metal (TM) alloys, such as GdFeCo,[2] all-optical helicity-dependent switching (AO-HDS) represents a fast and facile method to manipulate magnetizastructures opens a novel route toward practical opto-spintronics
In the Synthetic ferrimagnets (SFi) Hall bars, anomalous Hall effect (AHE) measurements, VHall (Section S1, Supporting Information) provide an electrical measurement sensitive to Mz of each layer, and confirm remnant states I and II are maintained in the patterned films

Summary

Results and Discussion

We perform measurements on micrometer-scale SFi Hall bars consisting of two perpendicularly magnetized, AF-coupled FM layers, termed FM1 (Co/Pt) and FM2 (CoFeB/Pt/CoFeB) and with variable thickness tCo and tCoFeB. We further studied the response of the SFi to light pulses with different laser fluence using the sweeping beam method (see Section S8, Supporting Information) With the beam fluence reduced to 1.5 mJ cm−2, a minimum in the demagnetization area and subsequent helicity-dependent switching is observed Using this laser fluence, the response of the SFi to light pulses using a fixed beam method is investigated (see Section S9, Supporting Information). A picture prevails where the laser pulse must provide sufficient heat for the FM to reach a temperature approaching TC, at which point light helicity can induce a symmetry-breaking reversal mechanism, such as the IFE, and lead to switching

Conclusion

Experimental Section

Conflict of Interest