Artificial Antiferromagnetic Multilayers Used In Spin Nano-oscillator

It is well known that electron has two intrinsic properties,charge and spin.The study of charge has promoted the development of traditional microelectronics.Since the end of the 20th century,spin,the other intrinsic properties of electrons,has attracted increasing attention.Spintronics,using charge and spin degrees of freedom simultaneously,has become an emerging discipline in material sciences.Novel spintronic devices such as high density MRAM and spin logic devices with low power consumption can be developed base on the generation,injection,transport and detection of the spin polarized electrical transport properties.The development and application of next generation spintronic devices are expected to overcome the bottleneck of microelectronics technology,resulting a great improvement of the information storage density and processing speed.In 1988,Grunberg and Fert reported the giant MR effect(GMR),which have made the magnetic recording technology to develop rapidly.Later,in the Al2O3 and MgO based magnetic tunneling junctions(MTJs).tunneling magnetoresistance(TMR)was observed.The magnetic recording density has been largely increased by utilizing the TMR effect.With the increase of storage density,more and more magnetic materials with high coercivity have been used in hard disk,which affects the rotation speed of magnetic head.In order to solve this problem,microwave assisted magnetic recording has emerged as a new technology to improve the speed of magnetic recording.When the magnetic moment is processing under the application of an external magnetic field,the applying of an additional microwave field can reduce the coercivity of the magnetic recording materials,which makes it easier to flip the magnetization direction of storage unit,thus improving the writing ability of the magnetic head.In order to apply high-frequency microwave on nanoscale,spin torque nano-oscillator(STNO)based on MTJ structure has been developed.STNO is a new class of nano-sized microwave device based on TMR and spin-transfer torque(STT)effect,which has promising application prospects in sensor,microwave communications and microwave detectors.The advantage of STNO includes simple structure,nanoscale size,low operating voltage and wide frequency range.Studies have shown that the structure and performance of MTJs directly affect the properties of STNO.To prepare MTJs with high stability and high power-output by using magnetron sputtering is an important goal of this thesis.Considering the fact that synthetic antiferromagnets(SAF)have the advantages of high stability and zero stray field,we use SAF structure as an additional pinning layer to pin the magnetic fixed layer.The TMR is 24.9%in IrMn/CoFe/Ru/CoFeB/MgO/CoFeB magnetic tunneling junctions with 1-nm thick MgO tunneling barrier.In CoFeB/MgO/CoFeB MTJs,top CoFeB sublayer with smaller coercivity is the f-ree layer.Previous reports indicates that Lutilizing synthetic antiferromagnets as the free layer in MTJ could enhance the thermal stability and reduce the critical switching current.Moreover,a larger precession angle,corresponding to a larger output signal.can be obtained in the STNO of orthogonal structure,where the easy plane of the magnetic fixed layer is in-plane while it is out of plane for the magnetic free layer.Therefore,we have fabricated perpendicularly magnetized[Pt/Co]N1/Ru/[Co/Pt]N2 synthetic antiferromagnets.And the influence of the exchange coupling and the variation of structure and cycle number on magnetization reversal has been investigated.laying the foundation for later applications.