Abstract
We investigated the temperature distribution induced by laser irradiation of ultrathin magnetic films by applying a finite element method (FEM) to the finite difference time domain (FDTD) representation for the analysis of thermal induced spin currents. The dependency of the thermal gradient (∇T) of ultrathin magnetic films on material parameters, including the reflectivity and absorption coefficient were evaluated by examining optical effects, which indicates that reflectance (R) and the apparent absorption coefficient (α*) play important roles in the calculation of ∇T for ultrathin layers. The experimental and calculated values of R and α* for the ultrathin magnetic layers irradiated by laser-driven heat sources estimated using the combined FDTD and FEM method are in good agreement for the amorphous CoFeB and crystalline Co layers of thicknesses ranging from 3~20 nm. Our results demonstrate that the optical parameters are crucial for the estimation of the temperature gradient induced by laser illumination for the study of thermally generated spin currents and related phenomena.
Highlights
We investigated the temperature distribution induced by laser irradiation of ultrathin magnetic films by applying a finite element method (FEM) to the finite difference time domain (FDTD) representation for the analysis of thermal induced spin currents
We propose a unique way through combining the finite difference time domain (FDTD) and a finite element method (FEM) to unravel the optical and thermal interrelated problems while calculating the ∇T in ultrathin layers
We used a longitudinal spin Seebeck effect (LSSE) geometry with the laser irradiation method shown in Fig. 1(a) as a model system for calculating ∇T in ultrathin films[19,20]
Summary
We investigated the temperature distribution induced by laser irradiation of ultrathin magnetic films by applying a finite element method (FEM) to the finite difference time domain (FDTD) representation for the analysis of thermal induced spin currents. The application of thermal gradients (∇T) to magnetic nanostructures has opened a new era of spin current generation in the field of spintronics[1,2,3,4,5] These novel spin current generation methods have enabled the discovery of the spin counterparts of the Nernst and Seebeck effects, and unify the spin-degree of freedom with thermoelectrics (TE). In the heat transfer equation, the external heat source and heat transport are defined by the optical and thermal parameters of ultrathin films correlated with the incident laser-power distribution and thermal conductivity (κ) They must be determined carefully for the precise estimation of ∇T. Our formulated approach is useful for overcoming the complexities associated with experimental procedures for obtaining the values of the effective optical parameters required for accurately estimating ΔT and the precise ∇T in ultrathin films
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