Synchrotron Radiation Time-Resolved X-Ray Ferromagnetic Resonance Experimental Device And Its Application

The information storage using electron spin as the carrier has made a revolutionary improvement in magnetic storage technology,and spintronics has emerged as a branch of the field of magnetism.Spintronic devices based on spintronics have developed rapidly due to their advantages of non-volatile power-off,strong anti-interference ability,high storage speed and low power consumption.The study of the generation,transport,regulation,and detection of electron spins is an important aspect of spintronics.To study the spin-flip mechanism of spintronic devices and improve the flipping speed and stability,it is extremely important to study the flipping dynamics of spintronic devices on the picosecond scale.The time-resolved X-ray ferromagnetic resonance（TR-XFMR）method based on synchrotron radiation can be used to study the precession of the electron spin of specific elements in materials,which is an important tool for studying the spin dynamics of spintronic devices.In this paper,an experimental apparatus of picosecond time-resolved X-ray ferromagnetic resonance with a time resolution of 13 ps RMS was demonstrated at the soft X-ray beamline 07U and 08U1A in the Shanghai Synchrotron Radiation Facility（SSRF）.An experimental apparatus of picosecond time-resolved X-ray ferromagnetic resonance with a time resolution of 13 ps root mean square（RMS）was demonstrated and constructed at the Shanghai Synchrotron Radiation Facility.It applied for a pump-probe detection technique and combined with X-ray magnetic circular dichroism spectroscopy.Under a constant bias field and the microwave field,ferromagnetic materials are excited to generate the spin precession.Left and right circularly polarized X-rays are utilized to detect the components of the magnetic moment paralleling to the direction of the photon beam.The phases of the microwave and the photon bunch clock are synchronized using a set of electronic devices.The spin dynamics can be directly measured.The experimental apparatus is equipped with the timing system,the XFMR electronic circuitry system and the microwave excitation.For the timing system,the phase-locking and the adjustable time delay between the microwave and the X-ray pulse with a step resolution of 5 ps have been achieved.For the XFMR electronic circuitry system,the microwave frequency can be multiplied to gigahertz band.Meanwhile,microwave power is flexibly modulated and can be monitored in real time.The coplanar waveguide is used as a microwave excitation device,and the microwave magnetic field can reach 8 Gs when the input power is 1 W.With the apparatus,we measured the Ni moment precession during ferromagnetic resonance in permalloy(Ni₈₁Fe₁₉ layer).Under a microwave magnetic field of 2.5 GHz,the spin precession of the Ni element in permalloy was driven.The time-dependent curve of the projection of the spin precession cone angle of Ni element along the beam direction was tested.The experimental results demonstrated that the experimental platform can excite magnetic elements to generate spin precession at GHz and detect the amplitude and phase of spin precession on a picosecond time scale.Furthermore,the spin pumping effect was investigated in Ni₈₁Fe₁₉/Pt/Co₉₀Fe₁₀ multilayers with the apparatus.Under the microwave magnetic field at 2 GHz,the spin precession of Ni element was driven in the Ni₈₁Fe₁₉film.Due to the spin pumping effect,the Ni₈₁Fe₁₉film would generate a pure spin current that was injected into the adjacent Pt film and then transported to the Co₉₀Fe₁₀ film,driving the spin precession of the Co₉₀Fe₁₀ film coherently.The time-dependent curve of the projection of the spin precession cone angle of Co and Ni element along the beam direction was tested.The experimental results show that the experimental device can achieve directly detect the spin current.Based on this device,the spin transport was further studied,and the effect of interface between Ni₈₁Fe₁₉/Ta system for three different crystalline phases of the Ta layer on spin current transport was mainly studied.In the ferromagnetic/heavy metal bilayer structure,the ferromagnetic material underwent ferromagnetic resonance under the microwave magnetic field and the steady magnetic field,which would inject pure spin current into the adjacent heavy metal film.Due to the inverse spin Hall effect,the spin current was converted into a charge current within the heavy metal film.The pumping of spin currents from ferromagnetic thin film to adjacent heavy metal film could be described by the effective spin-mixing conductance.The effective spin-mixing conductance represented the generation efficiency of spin currents and could be calculated from ferromagnetic resonance measurements.However,at the interface of the ferromagnetic/heavy metal bilayer system,due to the scattering mechanism,part of the spin current was absorbed,that is,the spin memory loss,which reduces the actual spin current injecting into the heavy metal film.The voltage also decreased.In this study,three different crystalline phases of the Ta layer are deposited using DC magnetron sputtering annealing technology at different temperatures.After the ferromagnetic resonance and inverse spin Hall voltage measurements of different samples,the experimental results show that the Ni₈₁Fe₁₉/（α+β）-Ta bilayer has the largest spin-mixing conductance and the highest spin injection efficiency,but its spin memory loss is relatively large.The interface inhibits the transport of the spin current,and the actual injection of the spin current into the heavy metal film is small;in contrast,the spin pumping efficiency of the Ni₈₁Fe₁₉/α-Ta bilayer film is not high,but its interface has the smallest spin memory loss and the largest inverse spin Hall voltage.