Abstract
There is a lot of experimental evidence of All Optical Switching (AOS) by applying ultrashort laser pulses on ferromagnetic thin films with perpendicular magnetic anisotropy. However, the physical origin behind these processes remains under debate. In addition to the heating caused by the laser pulses, the Inverse Faraday Effect (IFE) and Magnetic Circular Dichroism (MCD) have been proposed as the most probable phenomena responsible for the observations of helicity-dependent AOS. Here, we review the influence of both phenomena by means of realistic micromagnetic simulations based on the Landau–Lifshitz–Bloch equation coupled to the heat transport caused by the laser heating. The analysis allows us to reveal the similarities and differences between both effects. While both mechanisms may lead to the local inversion of the initial magnetic state of a ferromagnetic sample submitted to a train of circularly polarized laser pulses, the Inverse Faraday Effect proves to be more efficient for nucleation and domain wall movement and it reproduces more accurately the different magnetic configurations that the experiments report for different values of the fluence of the laser beam.
Highlights
Manipulation of magnetism using ultrafast laser pulses without any external magnetic field, called All Optical Switching (AOS), is fundamentally interesting and promises for low-power and high-speed spintronic devices
We present a full micromagnetic formalism based on a model that couples the laser heating, described by the two temperatures model (2TM) [3,12], to the magnetization dynamics governed by the stochastic LLB Equation [12,27], which includes the transient magnetic field caused by the Inverse Faraday Effect (IFE)
Before analyzing the role of IFE and Magnetic Circular Dichroism (MCD) in these Helicity-Dependent All Optical Switching (HD-AOS) processes, we first describe the heating caused by the laser, which is common for both IFE and MCD scenarios
Summary
Manipulation of magnetism using ultrafast laser pulses without any external magnetic field, called All Optical Switching (AOS), is fundamentally interesting and promises for low-power and high-speed spintronic devices. The optical control of the magnetic state in a ferromagnetic sample usually requires series of laser pulses with circular polarization This multi-shot helicity-dependent control of the magnetization has been observed in three different types of experiments. It has not been possible to realistically elucidate the real role of the IFE and the MCD in helicity-dependent all-optical switching or domain wall motion processes, which is precisely the aim of the present work. We present a full micromagnetic formalism based on a model that couples the laser heating, described by the two temperatures model (2TM) [3,12], to the magnetization dynamics governed by the stochastic LLB Equation [12,27], which includes the transient magnetic field caused by the IFE and/or the different energy absorption rates due to the MCD.
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