Study On The Spin-seebeck Effect Of Ferromagnetic Films

The spin-Seebeck effect(SSE) refers to the generation of a spin voltage as a result of a temperature gradient in magnetic materials, and becomes a hot issue in the field of spintronics. However, the exact value of the SSE of ferromagnetic metal is still unknown and there are hardly any reports on the coexisted SSE and spin Hall magnetoresistance(SMR). In this thesis, we researched the SSE in Pt/Py(Pt/Ni81Fe19) structure and measured the Joule heating-induced coexisted SSE and SMR in the Pt/YIG(Pt/Y3Fe5O12) structure.Firstly, the geometric distribution of the spin voltage in Pt/Py structure, which was generated by the SSE, was analyzed by the Diffusion Equation in details. The inverse spin-Hall voltage(VISHE) depends on local thickness of Py film, the thicker is the local Py film, the bigger is VISHE and then it tends to a constant. At the same time, finite element numerical analysis method was used to simulate the short-circuit-effect in each sample. The exact magnitude of short-circuit-effect was got and the thicker is the local Py, the more obvious is the short-circuit-effect for the VISHE in Pt. Considering these two factors, we fabricated Pt/Py samples with different thickness of Py and measured VISHE where the Anomalous and Planar Nernst Effects(ANE and PNE) was excluded. With theoretical calculations, the spin-diffusion length of Py is 18 nm. So we put forward a new method to measure the spin-diffusion length.Furthermore, Joule heating-induced coexisted SSE and SMR in the Pt/YIG structure were studied in details. We measured VISHE and SMR in Pt/YIG structures of different thickness of Pt by current self-heating experimental device. The VISHE and SMR were separated because they had different parity dependence on current. Their relationships with angle ? were also researched. We excluded the Pt's magnetization from YIG by Pt/Cu/YIG structure and summarized the conclusion as follows. The thinner is the Pt, the greater is the VISHE and SMR. The SSE and SMR exhibits a cos? and sin2? variation with ? respectively. In order to make clear the relationship between the SSE and SMR, we calculated their corresponding spin currents. The spin current of the SSE exhibits a quadratic dependence on current, which is reasonable because of its temperature dependence. However, the spin current of the SMR essentially linearly grows with current since the spin accumulation is caused by the spin transfer torque of current at the Pt/YIG interface. The SSE and SMR do not influence each other perhaps because their spin polarizations are perpendicular with each other.