| With the rapid progress in magnetic random access memory(MRAM)industry,perpendicular magnetic tunnel junction(P-MTJ)material with high perpendicular magnetic anisotropy(PMA)and large tunneling magnetic resistance(TMR)are urgently demanded.Nowadays,the ST-MRAM with spin transfer torque(ST)and P-MTJ as the core is becomes more mature,how to further improve the magnetization switch speed and how to reduce energy consumption is the key issues for the development of MRAM.Meanwhile,the last-model of SOT-MRAM with combining spin orbit torque(SOT)and P-MTJ and use skyrmion as storage mediums are two directions of information storage development in the future.At present,the dynamics of ferromagnetic layer in the process of magnetization reversal in the spin valve structure is one of the most fascinating subjects.Therefore,the paper focuses on the exploration of new perpandicular anisotropic materials and control their spin states.The main research and results are as following:(1)Mo/FeNiB/MgO and its inverted structure MgO/FeNiB/Mo have been fabricated by magnetic sputter,which show large PMA and high thermal stability within a certain thickness range,it ensures spontaneous perpendicular magnetization with effective PMA field of about 5 kOe in Mo/FeNiB(1.2 nm)/MgO and MgO/FeNiB(1.5 nm)/Mo after annealing at 400? in vacuum chamber,comparable to the CoFeB/MgO system.Remarkably,the coercivity of perpendicularly magnetized FeNiB layers in either continuous film or patterned structure of micrometers is smaller than that of the CoFeB counterpart by an order.We have fabricated perpendicular magnetic tunnel junctions with pseudo-spin valve structure Mo/FeNiB/MgO/CoFeB/Mo,which show TMR of 113%at room temperature and 221%at 5 K.These results suggest that Mo/FeNiB/MgO heterostructure can be as a candidate material for developing the next generation core unit of spintronic devices.(2)A series of Pt/WB/FeNiB/MgO multilayer films with perpendicular magnetic anisotropy were prepared by magnetron sputtering.Its perpendicular anisotropy field is greater than 4000 Oe,and its temperature stability better than 350?.In the hetero-junction,the spin-orbit torque generated by direct currents or pulse currents,which can switch the magnetization of FeNiB effectively.When applied external magnetic field with 200 Oe,the critical current density is about 1.6×107 A/cm2,which approach the valve of CoFeB/MgO.We further find the magnetization switch is dominated by the damping-like effective field,which measured by using the second harmonic method(3)The magnetic skyrmions in the multilayer structure are considered as a new direction for the next generation of storage due to their small size,robustness against external perturbations,high electric current-driven mobility,and the compatibility with the existing spintronic technology.We systematically studied the evolution of Neel-type magnetic skyrmion in Mo/FeNiB/MgO multilayer structures with perpendicular magnetic anisotropy,where magnetic anisotropy changes from PMA to in-plane magnetic anisotropy(IPA)as the thickness of FeNiB layer increases.By adjusting the applied magnetic field and/or applied current,the stable high-density skyrmions state can be obtained in the system.The discovery of this material broadens the exploration of new materials and accelerate the development of skyrmion-based spintronic devices(4)Magnetic damping of the free layer CoFeB in spin-valve IrMn/CoFe/Cu/CoFeB with very large exchange bias has been characterized by frequency-swept ferromagnetic resonance under varied magnetic field.The damping constant of the CoFeB layer shows no difference between the parallel and antiparallel configuration of the two magnetic layers,consistent with the theoretical prediction.Moreover,in the intermediate states during the pinned CoFe magnetization reversal,the effective damping constant is significantly enhanced from 0.012 up to 0.029.This remarkable enhancement,exceeding the effect of the pumped spin current appreciably,is mainly due to the inhomogeneous broadening and/or two-magnon scattering caused by the stray field emerging from the domain walls of the pinned CoFe layer under reversal Meanwhile,resonance frequency shift is also observed because of the domain wall induced coupling.Our result convincingly confirms the significant influence of the fixed layer domain wall induced coupling on the magnetic damping in spin-valves,which should be properly excluded while discussing the nonlocal spin transport induced damping in heterostructures.This conclusion also applies to the magnetic tunnel junction of IrMn CoFe/Ta/CoFeB/MgO/CoFeB. |
PDF Full Text Request