Investigation On Magnetism And Electrical Transport Properties Of Ferrimagnetic GdFeCo-based Multilayer Films

The 21 st century is an information age centered on the Internet.Digitalization,networking,and informatization are the basic characteristics of this era,and the ever-developing computer technology has higher and higher requirements for information storage.Spintronics is a research field that can manipulate spin at the nanometer scale and can be used to develop and manufacture a new generation of information storage devices.For example,Magnetic random access memory(MRAM)has extremely essencial application prospects due to it possesses many advantages,which includes non-volatile,high density,low power consumption and high speed.At present,devices based on ferromagnetic materials have achieved great success in sensors and data storage.However,as the size of the devices is further reduced,the problem of heat dissipation has seriously hindered the further development of spintronic devices.In recent years,ferrimagnetic materials with anti-parallel magnetic moment arrangement characteristics have shown many excellent properties.For example,magnetic moment and angular momentum can cancel each other out generates the smaller net magnetic moment and stray field;the ultra-fast dynamics near the compensation point attachment;with bulk perpendicular anisotropy and longer spin coherence length.These characteristics have caused many novel physical phenomena,making them have broad application prospects in electronic devices such as magnetic sensors,high-density storage,and integrated sensing components.Rare earth-transition metal ferrimagnetic alloy is an important potential candidate material for the preparation of such devices.In this study,the rare earth-transition metal Gd Fe Co ferrimagnetic alloy thin film and the magnetic multilayer film based on it are prepared by magnetron sputtering method,and the structure,magnetic properties and electrical transport properties of the thin film are studied.The main research contents are as follows:(1)Magnetron sputtering was used to prepare magnetic multilayer films such as Pt/Gd Fe Co/Pt and Pt/Gd Fe Co/Ta to study the structure and magnetic properties of the films.By controlling the Gd content and the Gd Fe Co growth rate,the magnetism is regulated.The hysteresis loop results show that according to increasing the Gd content and reducing the Gd Fe Co growth rate can cause the easy axis of the film to change from the in-plane direction to the out-of-plane direction and finally optimized high-quality Pt/Gd Fe Co/Pt and Pt/Gd Fe Co/Ta multilayer films with small surface roughness,low saturation magnetization,and excellent perpendicular magnetic anisotropy.At the same time,it is clarified that the perpendicular magnetic anisotropy originates from the strong spin-orbit coupling effect at the heavy metal/Gd Fe Co interface.(2)Based on the Gd Fe Co-based multilayer film with good perpendicular magnetic anisotropy optimized,the influence of the external magnetic field on the exchange bias of the multilayer film was further studied.A spontaneous exchange bias phenomenon related to the initial magnetization state was observed in the Pt/Gd Fe Co/Pt multilayer film,and this spontaneous exchange bias phenomenon was verified by an abnormal Hall effect test.In addition,the experimental results show that the exchange bias field can be effectively controlled by changing the size and direction of the initial external magnetic field.The generation mechanism may be related to the special inclined magnetic structure on the surface of the Gd Fe Co magnetic layer.(3)The novel physical phenomena of Gd Fe Co-based multilayer films were further explored through electrical transport tests.When the Gd content is low,the multilayer film exhibits an abnormal Hall effect of superimposed topological signal at room temperature;the abnormal Hall effect that changes the sign of the Hall coefficient with temperature is observed in the perpendicular anisotropic multilayer film with higher Gd content,the topological Hall effect of the antiferromagnetic state is detected near the compensation point,and the spin current generated by the spin Hall effect effectively drives the antiferromagnetic Gd Fe Co layer to achieve magnetization reversal.