Perpendicular Magnecit Anisotropy And Spin Hall Effect In Heterostructure Films

Because of the insulating nature,extremely low Gilbert damping,and large magnon decay length,in recent years,the thin YIG film has attracted significant interest in spintronics,and it greatly facilitates the research on spin pumping,spin caloritronics,magnonics,and even topological spintronics.The YIG films?as well as many other rare-earth iron garnet films?usually favor in-plane spontaneous magnetization due to the overwhelming shape anisotropy.With the rapid progress in spintronics,nanometer-thick insulating magnetic films with perpendicular magnetic anisotropy?PMA?are becoming more appealing.For example,the geometry for spin-wave transport requires the magnetization orthogonal to the propagation direction in magnonics;nonvolatile magnetic memories and logic devices based on insulating perpendicular magnetic films switched by spin-orbit torque?SOT?will significantly reduce heat dissipation in comparison with the all-metallic counterpart;heterostructures consisting of a topological insulator and an insulating magnetic layer with PMA are regarded as a promising approach to realize the quantum anomalous Hall effect and other topological magnetoelectric effects.Therefore,insulating perpendicular magnetic thin films and their heterostructures have been the subject of increasing interest.The development of YIG films with large PMA seems to be more challenging.It has been reported that YIG thin films with PMA have been successfully prepared on a single crystal garnet substrate with lattice constants exceeding that of YIG by a ratio1.41%via a specific buffer layer by pulsed laser deposition,and the complex preparation process and a rather gentle PMA are not favor for its further development.In this paper,high quality epitaxial?111?YIG films with the tunable PMA are fabricated by annealing amorphous precursor films that are sputtering deposited on three kinds of single crystal garnet substrates with lattice constants exceeding that of YIG by a ratio from 0.76%to 1.58%.Large PMA is demonstrated in the fully strained thin YIG films on substrates with lattice mismatch from 1.05%to 1.58%due to the overwhelming of the magnetoelastic anisotropy.Less-strained YIG films,corresponding to partial strain relaxation at larger YIG thickness or smaller substrate lattice mismatch at 0.76%,show substantial but insufficient magnetoelastic anisotropy to overcome shape anisotropy.Magnetotransport characterization on YIG/Pt bilayers shows the high quality YIG surface with efficient spin current transmission across the heterostructure interface.The present method should also be applicable to the epitaxial growth of other rare earth iron garnet thin films with unprecedented ability to acquire and control PMA.In spintronics,the generation and detection of spin currents have always been the focus of attention.The spin Hall effect and its inverse effect in metal and alloys are regarded as a promising way to generated and detect pure spin currents.The spin Hall angle represents the efficiency of the conversion between charge current and spin current.In the ferromagnetic metal/non-magnetic metal heterostructure,due to the spin Hall effect associated with spin-orbit coupling,the spin current generated by the current in non-magnetic metal is absorbed by the ferromagnet layer,and exerts a torque effect on the ferromagnetic layer.This is one of the most import sources of the spin-orbit torque.The spin-orbit torque can switch the magnetization of ferromagnetic materials and the corresponding critical current density is closely related to the spin Hall angle of non-magnetic metals.It is of great significance to find materials with large spin Hall angle.?-W is well-known for its a large spin Hall angle,but it is unstable.After high temperature annealing,phase transition is easy to occur,?-W is transformed into stable?phase,and the spin Hall angle decreases greatly.Therefore,it has been reported that the W/CoFeB/MgO heterostructures with PMA and significant spin-orbit torque can not be annealed above 300°C,which is much lower than 350-400°C required for semiconductor CMOS integration.A W-B alloy with large spin Hall angle and temperature stability better than 350°C was prepared,and the W-B/CoFeB/MgO heterostructures with PMA was obtained.The magnetization switching of CoFeB is realized by the spin-orbit torque induced by DC and pulse current.When in-plane external field is 130 Oe,the critical current density is 2×10⁷ A/cm².We further find the spin-orbit torque of W-B/CoFeB/MgO is dominated by the damping-like effective field,and the spin Hall angle of W-B is-0.23,which is comparable to that of?-W with the same thickness.The effect of Cu buffer layer on the spin Hall effect of Ir₂₅Mn₇₅ is invesgated in this paper.The spin Seebeck effect and spin pumping technique are used to measure YIG/Ir₂₅Mn₇₅ and YIG/Cu/Ir₂₅Mn₇₅ heterostructure films,we found that the presence of Cu layer resulted in a larger inverse spin Hall voltage of Ir₂₅Mn₇₅.The results of magnetic characterization show that the crystallinity of Ir₂₅Mn₇₅ grown on YIG is poor and the antiferromagnetism decreases at room temperature,while Ir₂₅Mn₇₅ in YIG/Cu/Ir₂₅Mn₇₅ has better crystallinity and antiferromagnetism.The oxidation of Mn in was tested by angular resolved X-ray photoelectron spectroscopy.The results show that Mn exists in metallic phase and the oxidation is not obvious.The interfacial spin mixing conductance of YIG/Cu/Ir₂₅Mn₇₅ is slightly larger than that of YIG/Ir₂₅Mn₇₅ by ferromagnetic resonance measurements.Therefore,the increase of inverse spin Hall voltage of Ir₂₅Mn₇₅ in YIG/Cu/Ir₂₅Mn₇₅ is mainly due to the effect of buffer layer Cu on the microstructure and corresponding antiferromagnetism of Ir₂₅Mn₇₅.