Simulation And Reserch On The Mechanism Of All-Optical Switching Of GdFeCo Amorphous Alloy

The rapid development of Internet of Things,artificial intelligence,5G communication and other technologies has led to the explosive growth of data volume.Faced with such a huge amount of data,it is particularly important to improve the reading and writing speed and capacity of storage devices.All-Optical Switching(AOS)technology is a new method to obtain faster reading and writing speed and more efficient data storage.Femtosecond laser writing heads are used to replace traditional writing heads,which can boost writing ability to a new level,so that the writing speed of information can be qualitatively improved.However,in order to achieve the new femtosecond laser ultrafast all-optical magnetic recording,not only need study the condition to realize all-optical magnetization switching,more important is to understand the physical mechanism of magnetization reversal induced by ultrafast femtosecond laser,and explore the factors affecting the stability and speed of magnetization reversal,make the industrialization of all-optical magnetic recording technology plausible.Rare Earth-Transition Metal(RE-TM)alloy ferrimagnetic thin films possess excellent photomagnetic properties,and can undergo ultrafast magnetization reversal in subpicosecond time scale after being excited by photons,which is of great research value.In this paper,the atomic scale spin model of Gd Fe amorphous alloy was constructed by calculating the system Hamiltonian of Gd Fe alloy system.Based on the atomic LLG equation,the effects of the ratio of rare earth to transition metal elements and the incident laser power density have been studied.The dynamic process of sublattices magnetization of Gd₂₅Fe₇₅ amorphous alloy caused by pure thermal effect of femtosecond laser is solved by utilizing Heun integral method,and the irrationality of pure thermal magnetization switching is revealed.The macroscopic spin transfer torque effect is modified to the microscopic representation suitable for atomic-scale model,and the spin transfer torque term is added into the atomic LLG equation to simulate the combined effect of pure thermal effect,spin transfer torque effect and atom exchange interaction caused by femtosecond laser.By analyzing the spin dynamics simulation results of two different sublattice Gd and Fe,and referring to the experimental results of Graves et al.,it is clear that there is an optimal laser energy density"window"within which the AOS process of Gd₂₅Fe₇₅ amorphous alloy can be completed more quickly and stably.Finally,a possible physical mechanism of helicity independently AOS in RE-TM alloy has been explored.It is of great significance to promote the practical application of AOS storage technology.In summary,this paper proposed a physical mechanism to explain the helicity independently AOS phenomenon in RE-TM alloy,and established the atomic-scale model for describing the related physical process,the AOS characteristics of GdFeCo alloy were studied thoroughly by means of simulation calculation,the important role of spin transfer torque effect in spin magnetic moment reversal process of Fe atoms is demonstrated,which provides a new idea for subsequent experimental and theoretical research.