| The charge and spin properties of electrons are fundamental to the development and innovation of the human information technology industry.The charge attribute is applied to human production and life,and the birth of traditional electronics has led to the rapid development of the information industry and related industrial fields.Spintronics is a new subject which uses the spin properties of electrons,and has become a mainstay to promote the development of the information industry.The discovery of the GMR effect in 1988 has brought a bright future for the magnetic storage technology.IBM company in the United States successfully explored a GMR-based magnetic head.Subsequently,the magnetic storage technology based on the tunneling magnetoresistance(TMR)effect can greatly improve the original information storage method,increase the information storage speed and density,and reduce the power consumption of the device.In 2001,TDK successfully developed a TMR-based hard disk.In order to achieve higher storage density,magnetic materials with higher coercivity are required.However the application of these materials will obviously affect the magnetic moment switching.Therefore,microwave-assisted magnetic recording has been developed through the tireless efforts of many scientists.Using the spin transfer torque(STT)effect,under the combined effect of the microwave field and the external magnetic field,it can effectively reduce the coercivity and improve the storage capacity.The spin nano-oscillator is the key technology of microwave-assisted magnetic recording.Compared with the current semiconductor storage technology,the spin nano-oscillator has outstanding advantages,for example,simpler structure,smaller volume,and wider frequency range(0.1～100 GHz),etc.It is a new type of spin electronic device based on the effect of spin polarization current,which enables the magnetic moment of free layer to stably precess around the effective field,therefore it can output high frequency microwave signals.The spin nano-oscillator based on the MgO magnetic tunnel junction has the best development prospects and already has a mature preparation system.In this thesis,the MgO-based magnetic tunnel junction is used as the tunnel junction structure of the spin nano-oscillator,and the microwave emission characteristics of the spin nano-oscillator are studied.Research on the microwave characteristics of spin nano-oscillators has high requirements on the quality of CoFeB/MgO/CoFeB magnetic tunnel junctions.The magnetic multilayer film is prepared by magnetron sputtering with a base vacuum better than 5×10-6 Pa,and the magnetic tunnel junctions are prepared by photolithography and etching technology.We measured the microwave emission characteristics of four types of STNO structures—:coplanar-type in-plane magnetized structure,coplanar-type inclined magnetized structure,orthogonal-type in-plane magnetized structure,and orthogonal-type inclined magnetized structure.Using the shape anisotropy of the free layer of the magnetic tunnel junction,the microwave emission characteristics at zero magnetic field were measured in a tilted magnetized structure.Among them,the results of the orthogonal in-plane magnetization structure are the most prominent,and the excellent microwave power density output at room temperature and zero magnetic field has been successfully obtained,and it has a good oscillation frequency.At the same time,we also measured the microwave characteristics and wireless transmission microwave characteristics of STNO devices with multiple magnetic tunnel junctions in series,and both measured obtained the microwave emission characteristics under zero magnetic field. |
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