Role of element-specific damping in ultrafast, helicity-independent, all-optical switching dynamics in amorphous (Gd,Tb)Co thin films

Alejandro Ceballos, Akshay Pattabi, Amal El-Ghazaly, Sergiu Ruta, Christian P. Simon, Richard F.L. Evans, Thomas Ostler, Roy W. Chantrell, Ellis Kennedy, Mary Scott, Jeffrey Bokor, Frances Hellman

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Ultrafast control of the magnetization in ps timescales by fs laser pulses offers an attractive avenue for applications such as fast magnetic devices for logic and memory. However, ultrafast helicity-independent all-optical switching (HI-AOS) of the magnetization has thus far only been observed in Gd-based, ferrimagnetic amorphous (a-) rare earth-transition metal (a-RE-TM) systems, and a comprehensive understanding of the reversal mechanism remains elusive. Here, we report HI-AOS in ferrimagnetic a-Gd22-xTbxCo78 thin films, from x=0 to 18, and elucidate the role of Gd in HI-AOS in a-RE-TM alloys and multilayers. Increasing Tb content results in increasing perpendicular magnetic anisotropy and coercivity, without modifying magnetization density, and slower remagnetization rates and higher critical fluences for switching but still shows picosecond HI-AOS. Simulations of the atomistic spin dynamics based on the two-temperature model reproduce these results qualitatively and predict that the lower damping on the RE sublattice arising from the small spin-orbit coupling of Gd (with L=0) is instrumental for the faster dynamics and lower critical fluences of the Gd-rich alloys. Annealing a-Gd10Tb12Co78 leads to slower dynamics which we argue is due to an increase in damping. These simulations strongly indicate that accounting for element-specific damping is crucial in understanding HI-AOS phenomena. The results suggest that engineering the element-specific damping of materials can open up new classes of materials that exhibit low-energy, ultrafast HI-AOS.

Original languageEnglish
Article number024438
JournalPhysical Review B
Issue number2
Publication statusPublished - 25 Jan 2021

Bibliographical note

Funding Information:
This work was primarily supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the US Department of Energy under Contract No. DE-AC02-05-CH11231 within the Nonequilibrium Magnetic Materials Program (KC2204). Ultrafast laser measurements were supported by the NSF Center for Energy Efficient Electronics Science. A.C. acknowledges support by the National Science Foundation under Grant No. DGE 1106400. This project has received funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement No. 737093 (FEMTOTERABYTE). The atomistic simulations were undertaken on the viking cluster, which is a high performance compute facility provided by the University of York. We are grateful for computational support from the University of York High Performance Computing service, viking , and the Research Computing team.

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