Study On Spin-dependent Transportation In Nano-heterojunction

The spin-orbit torques effect has become the research focus by virtue of high integrated density,high read/write speeds and low power consumption.Using a spin current instead of a magnetic field to realize the manipulation of magnetic moments is the key to the practical application of spintronics.Understanding the physical mechanism of the spin-orbit torques effect,regulating the switching current and the effective field induced by spin-orbit torque effects,as well as establishing the correlation between charge current and heat current to achieve multi-degrees of freedom coupling are a key scientific problem for the development of spin-orbit torque effects.In this thesis,the temperature dependence of spin-orbit torques in Pt/Co/Pt heterojunction and the correlation between electrical transport and heat transport in Fe Co/Cu/Fe Ni heterojunction have been studied.The main conclusions are as follows:1? Based on the free energy of ferromagnetic metal/nonmagnetic heavy metal heterojunction,we have proposed the measurement method about effective field induced by spin-orbit torque effects in the out-of-plane and in-plane magnetization systems,which provides a theoretical foundation to study of the spin-orbit torques.2? We studied the temperature dependence of spin-orbit torques in perpendicularly magnetized Pt/Co/Pt heterojunction by harmonic Hall voltage measurements.Compared with the asymmetrical heterojunction,the damping-like torque has been obviously influenced by temperature due to the symmetrical Pt/Co interface.When temperature increases from 50 to 300 K,the damping-like torque increases from 3.7×10-6 Oe/(A·cm-2)to 4.8×10-6 Oe/(A·cm-2).Meanwhile,the lower switching current density(2.30 × 106 A/cm2)and the higher spin hall efficiency(0.15)were observed at 300 K.Finally,the temperature dependence of damping-like torque has been explained by the intrinsic spin Hall mechanism and magnetic proximity effect,and we find that the spin-swapping model may dominate the temperature dependence of fieldlike torque in the system with weaker Rashba effect.3? We have investigated the asymmetry parameter and the spin-dependent Seebeck coefficient in Fe Co/Cu/Fe Ni heterojunction as a function of temperature.The asymmetry parameter decreases from 1.37 to 1.30 and the absolute value of spin-dependent Seebeck coefficient increases from0.10 to 0.24 e V-1 from 100 to 300 K.It is more important that asymmetry parameter and spindependent Seebeck coefficient obey a simple liner relationship in the whole temperature range.Our results suggest that electrical transport and heat transport arise from a common scattering mechanism from the nonmagnetic s bands into the magnetic d bands in the charge(heat)currentin-plane spin-valve and can be described by the Mott scattering picture.