The spintronic devices are promising for non-volatile memory applications. Conventional spintronic devices using the precessional dynamics for magnetization switching are limited in future memory applications due to their large energy consumption and low operational speed. The development of future spintronic devices relies on the ultrafast and energy-efficient control of magnetization and magnetic textures. The emergence of ultrafast magnetism has introduced a new energy-efficient method for controlling magnetization at subpicosecond timescales through non-equilibrium heating generated by femtosecond laser pulses. This work uses atomistic spin dynamics simulations to explore various ultrafast phenomena induced by femtosecond laser pulses in rare earth-transition metal alloy ferrimagnets. This thesis has two parts. The first part (Chapters 3 & 4) focuses on helicity-independent all-optical switching (HI-AOS) in amorphous TbCo ferrimagnet. In Chapter 3, we evaluate the temperature dependence of static magnetic properties of TbCo for a range of compositions, from 18% Tb to 36% Tb. This includes calculations of the temperature dependence of magnetization, uniaxial anisotropy, and coercivity using Monte Carlo, constrained Monte Carlo and LLG Heun methods, respectively. In Chapter 4, we studied the potential for helicity-independent all-optical switching (HI-AOS) in amorphous TbCo. We identified a range of compositions where HI-AOS can occur and established a relationship between the critical laser fluence and Tb concentration. Further, we examined the impact of the damping constant on HI-AOS and demonstrated its significant influence on the process. The second part of this thesis (Chapters 5 and 6) focuses on creating and manipulating magnetic skyrmions in amorphous GdFeCo ferrimagnets using femtosecond laser pulses. Chapter 5 examines the ultrafast optical creation of magnetic skyrmions with a single laser pulse, exploring the microscopic mechanisms behind their nucleation. We also investigate the influence of laser parameters and external magnetic fields on the ultrafast laser-induced creation of magnetic skyrmions. Chapter 6 discusses the single-shot all-optical switching of the magnetic skyrmion core and chirality using HI-AOS. Our study demonstrates that HI-AOS can deterministically switch skyrmions at ultrafast timescales. Additionally, we investigate the role of laser fluence in skyrmion switching and find a fluence range where the switching is possible. In summary, our study demonstrates ultrafast, energy-efficient control of magnetization dynamics and magnetic skyrmions using femtosecond laser pulses. Our results offer valuable insights for implementing optical writing techniques in future spintronic devices.

2024

2024

2019

Indian Institute of Technology, Hyderabad

Phd