Spin Hall Magnetoresistance And Spin Seebeck Effect Of Heusler Alloy Films

The links among charge current,spin current and heat flow are interrelated and interconvert,which is the key to explore spin generation,injection,detection and manipulation.The spin Hall effect can convert the charge current into a spin one,and the inverse spin Hall effect reverses the spin current into a charge one to form a voltage,which can be used to measure the magnitude of the spin flow,and plays an important role in the spin Seebeck effect(SSE)and spin hall magnetoresistance(SMR)both.Spin Seebeck effect is the formation of spin voltage induced by temperature difference and provides a new direction for spin injection.The spin Seebeck effect is detected by the voltage formed by the inverse spin Hall effect in the Pt layer,while the spin Hall magnetoresistance is also due to the simultaneous action of the spin Hall effect and the reverse spin Hall effect.The spin-polarized electrons scattering by the magnetic moments lead to resistance changed,give hope to the quantitative analysis of spin current.Many Co-based Heusler alloys have100%spin polarizability because of their unique half-metal properties,and are also a typical thermoelectric material,but there are few studies on the spin dependent properties of the alloys.In this paper,the L2₁ structure of Co₂FeSi and Co₂Mn Sn films were prepared on Mg O substrates by magnetron sputtering.The spin Hall magnetoresistance in the Pt/Co₂Fe Si bilayer structure and the Co₂Fe Si/Pt/Co₂Fe Si trilayer structure was mainly studied.When the thickness of Pt is changed,the change of SMR and anisotropic magnetoresistance(AMR)of bilayer structure and trilayer structure is quite different individually with the temperature and the thickness of Pt.In the bilayer structure,when the thickness of the Pt layer is increased from 2nm to 8nm,the SMR decreases significantly and the decreasing trend of AMR is relatively mild;for samples with Pt thickness of 4nm,as the temperature increases from 50K to 300K,SMR increases first and then decreases,but AMR is decreasing and eventually tends to stabilize.Compared with the bilayer structure,the average SMR of the trilayer structure increases 4 times,but AMR decreases with the increase of the thickness of the Pt layer.It shows that the Co₂Fe Si/Pt boundary in the trilayer structure can greatly increase the magnitude of the spin current in the heavy metal Pt layer,and the trilayer structure can effectively enhance the SMR and inhibit AMR by adjusting the thickness of the Pt layer.The temperature dependence of SMR and AMR in the trilayer structure are also measured.The change of SMR in the trilayer structure is similar to that of the bilayer structure,but the result of AMR with the thickness of 2nm is the same as that of 4nm of the bilayer structure,while the Pt layer thickness is 4nm and8nm,AMR does not change with the temperature.This indicates that when the thickness of Pt is 2nm,the AMR of the trilayer is the same as that of the bilayer structure,all of which come from the magnetic proximity effect(MPE).However,when the thickness of Pt is increased to 4nm and 8nm,the MPE of the trilayer structure greatly reduces the AMR effect until it can be negligible,which provides a reference for the design and use of MPE to suppress the AMR in the spintronic devices.In this paper,the longitudinal spin Seebeck effect in the Co₂Mn Sn/Pt bilayer structure is also investigated.It is proved that the Co₂Mn Sn has a larger spin Seebeck coefficient than Ni Fe,which is predicted by the theory.