We present an overview in the understanding of spin-transfer torque(STT) induced magnetization dynamics in spintorque nano-oscillator(STNO) devices. The STNO contains an in-plane(IP) magnetized free layer and an out-o...We present an overview in the understanding of spin-transfer torque(STT) induced magnetization dynamics in spintorque nano-oscillator(STNO) devices. The STNO contains an in-plane(IP) magnetized free layer and an out-of-plane(OP) magnetized spin polarizing layer. After a brief introduction, we first use mesoscopic micromagnetic simulations,which are based on the Landau–Lifshitz–Gilbert equation including the STT effect, to specify how a spin-torque term may tune the magnetization precession orbits of the free layer, showing that the oscillator frequency is proportional to the current density and the z-component of the free layer magnetization. Next, we propose a pendulum-like model within the macrospin approximation to describe the dynamic properties in such type of STNOs. After that, we further show the procession dynamics of the STNOs excited by IP and OP dual spin-polarizers. Both the numerical simulations and analytical theory indicate that the precession frequency is linearly proportional to the spin-torque of the OP polarizer only and is irrelevant to the spin-torque of the IP polarizer. Finally, a promising approach of coordinate transformation from the laboratory frame to the rotation frame is introduced, by which the nonstationary OP magnetization precession process is therefore transformed into the stationary process in the rotation frame. Through this method, a promising digital frequency shift-key modulation technique is presented, in which the magnetization precession can be well controlled at a given orbit as well as its precession frequency can be tuned with the co-action of spin polarized current and magnetic field(or electric field) pulses.展开更多
We study magnetic proximity effect induced low-energy spin transport in the normal/ferromagnetic junction of a semi-infinite zigzag graphene nanoribbon. Due to the absence of a spin flip in a single interface, the spi...We study magnetic proximity effect induced low-energy spin transport in the normal/ferromagnetic junction of a semi-infinite zigzag graphene nanoribbon. Due to the absence of a spin flip in a single interface, the spin transfer in this model can be described by the ＂two-spin channel＂ model. We identify each spin channel as either a perfect conducting or a non-conducting channel. This feature leads to spin filter in symmetric zigzag graphene nanoribbon and spin precession in antisymmetric zigzag graphene nanoribbon, and helps to directly determine the exchange-splitting intensity directly, even without an external auxiliary bias.展开更多
Nano-ring-type magnetic tunnel junctions （NR-MTJs） with the layer structure of Ta（5）/Ir22Mn78（10）/ Co75Fe25（2）/Ru（0.75）/CoooFe20B20（3）/Al（0.6）-oxide/Co60Fe20B20（2.5）/Ta（3）/Ru（5） （thickness unit：...Nano-ring-type magnetic tunnel junctions （NR-MTJs） with the layer structure of Ta（5）/Ir22Mn78（10）/ Co75Fe25（2）/Ru（0.75）/CoooFe20B20（3）/Al（0.6）-oxide/Co60Fe20B20（2.5）/Ta（3）/Ru（5） （thickness unit： nm） were nano-fabricated on the Si（100）/SiO2 substrate using magnetron sputtering deposition combined with the optical lithography, electron beam lithography （EBL） and Ar ion-beam etching techniques. The smaller NR-MTJs with the inner- and outer-diameter of around 50 and 100 nm and also their corresponding NR-MTJ arrays were nano-patterned. The tunnelling magnetoresistance （TMR ＆ R） versus driving current （I） loops for a spin-polarized current switching were measured, and the TMR ratio of around 35% at room temperature were observed. The critical values of switching current for the free Co60Fe20B20 layer relative to the reference Co6oFe2oB2o layer between parallel and anti-parallel magnetization states were between 0.50 and 0.75 mA in such NR-MTJs. It is suggested that the applicable MRAM fabrication with the density and capacity higher than 256 Mbit/inch2 even 6 Gbite/inch2 are possible using both I NR-MTJ＋1 transistor structure and current switching mechanism based on based on our fabricated 4×4 MRAM demo devices.展开更多
Recent progresses in magnetic tunnel junctions with perpendicular magnetic anisotropy （PMA） are reviewed and summarized. At first, the concept and source of perpendicular magnetic anisotropy （PMA） are introduced. ...Recent progresses in magnetic tunnel junctions with perpendicular magnetic anisotropy （PMA） are reviewed and summarized. At first, the concept and source of perpendicular magnetic anisotropy （PMA） are introduced. Next, a historical overview of PMA materials as magnetic electrodes, such as the RE-TM alloys TbFeCo and GdFeCo, novel tetragonal manganese alloys Mn-Ga, L10-ordered （Co, Fe）/Pt alloy, multilayer film [Co, Fe, CoFe/Pt, Pd, Ni, AU]N, and ultra-thin magnetic metal/oxidized barrier is offered. The other part of the article focuses on the optimization and fabrication of CoFeB/MgO/CoFeB p-MTJs, which is thought to have high potential to meet the main demands for non-volatile magnetic random access memory.展开更多
We present first-principle calculations of electric and thermo spin transfer torques （STT） in Fe/Vacuum（Vac）/Fe magnetic tunnel junctions （MTJs）. Our quantitative studies demonstrate rich bias dependence of STT ...We present first-principle calculations of electric and thermo spin transfer torques （STT） in Fe/Vacuum（Vac）/Fe magnetic tunnel junctions （MTJs）. Our quantitative studies demonstrate rich bias dependence of STT and tunnel inagneto resistance （TMR） behaviors with respect to the interface roughness. Thermoelectric effects in Fe/Vac/Fe MTJs is remarkable. We observe larger ZT of 6.2 in 8 ML clean Vacuum barrier, where responsible for. Thermo-STT in Fe/Vac/Fe with similar barrier thickness. the heavily restraitmd thermal conductance should be MTJs show same order as that in Fe/MgO/Fe MTJs with similar barrier thickness.展开更多
基金supported by the National Basic Research Program of China(Grant No.2015CB921501)the National Natural Science Foundation of China(Grant Nos.11774260,51671057,and 11874120)
文摘We present an overview in the understanding of spin-transfer torque(STT) induced magnetization dynamics in spintorque nano-oscillator(STNO) devices. The STNO contains an in-plane(IP) magnetized free layer and an out-of-plane(OP) magnetized spin polarizing layer. After a brief introduction, we first use mesoscopic micromagnetic simulations,which are based on the Landau–Lifshitz–Gilbert equation including the STT effect, to specify how a spin-torque term may tune the magnetization precession orbits of the free layer, showing that the oscillator frequency is proportional to the current density and the z-component of the free layer magnetization. Next, we propose a pendulum-like model within the macrospin approximation to describe the dynamic properties in such type of STNOs. After that, we further show the procession dynamics of the STNOs excited by IP and OP dual spin-polarizers. Both the numerical simulations and analytical theory indicate that the precession frequency is linearly proportional to the spin-torque of the OP polarizer only and is irrelevant to the spin-torque of the IP polarizer. Finally, a promising approach of coordinate transformation from the laboratory frame to the rotation frame is introduced, by which the nonstationary OP magnetization precession process is therefore transformed into the stationary process in the rotation frame. Through this method, a promising digital frequency shift-key modulation technique is presented, in which the magnetization precession can be well controlled at a given orbit as well as its precession frequency can be tuned with the co-action of spin polarized current and magnetic field(or electric field) pulses.
文摘We study magnetic proximity effect induced low-energy spin transport in the normal/ferromagnetic junction of a semi-infinite zigzag graphene nanoribbon. Due to the absence of a spin flip in a single interface, the spin transfer in this model can be described by the ＂two-spin channel＂ model. We identify each spin channel as either a perfect conducting or a non-conducting channel. This feature leads to spin filter in symmetric zigzag graphene nanoribbon and spin precession in antisymmetric zigzag graphene nanoribbon, and helps to directly determine the exchange-splitting intensity directly, even without an external auxiliary bias.
基金the State Key Project of Fundamental Research of Ministry of Science and Technology （No. 2006CB932200） the National Natural Science Foundation of China （NSFC, No. 10574156）+2 种基金 the Knowledge Innovation Program of Chinese Aca.demy of Sciencesthe protial support of 0utstanding Young Researcher Foundation （Nos. 50325104 and 50528101） K.C.Wong Education Foundation, Hong Kong.
文摘Nano-ring-type magnetic tunnel junctions （NR-MTJs） with the layer structure of Ta（5）/Ir22Mn78（10）/ Co75Fe25（2）/Ru（0.75）/CoooFe20B20（3）/Al（0.6）-oxide/Co60Fe20B20（2.5）/Ta（3）/Ru（5） （thickness unit： nm） were nano-fabricated on the Si（100）/SiO2 substrate using magnetron sputtering deposition combined with the optical lithography, electron beam lithography （EBL） and Ar ion-beam etching techniques. The smaller NR-MTJs with the inner- and outer-diameter of around 50 and 100 nm and also their corresponding NR-MTJ arrays were nano-patterned. The tunnelling magnetoresistance （TMR ＆ R） versus driving current （I） loops for a spin-polarized current switching were measured, and the TMR ratio of around 35% at room temperature were observed. The critical values of switching current for the free Co60Fe20B20 layer relative to the reference Co6oFe2oB2o layer between parallel and anti-parallel magnetization states were between 0.50 and 0.75 mA in such NR-MTJs. It is suggested that the applicable MRAM fabrication with the density and capacity higher than 256 Mbit/inch2 even 6 Gbite/inch2 are possible using both I NR-MTJ＋1 transistor structure and current switching mechanism based on based on our fabricated 4×4 MRAM demo devices.
基金supported by the State Key Project of Fundamental Research of Ministry of Science and Technology,China(Grant No.2010CB934400)the National Natural Science Foundation of China(Grant Nos.51229101 and 11374351)
文摘Recent progresses in magnetic tunnel junctions with perpendicular magnetic anisotropy （PMA） are reviewed and summarized. At first, the concept and source of perpendicular magnetic anisotropy （PMA） are introduced. Next, a historical overview of PMA materials as magnetic electrodes, such as the RE-TM alloys TbFeCo and GdFeCo, novel tetragonal manganese alloys Mn-Ga, L10-ordered （Co, Fe）/Pt alloy, multilayer film [Co, Fe, CoFe/Pt, Pd, Ni, AU]N, and ultra-thin magnetic metal/oxidized barrier is offered. The other part of the article focuses on the optimization and fabrication of CoFeB/MgO/CoFeB p-MTJs, which is thought to have high potential to meet the main demands for non-volatile magnetic random access memory.
文摘We present first-principle calculations of electric and thermo spin transfer torques （STT） in Fe/Vacuum（Vac）/Fe magnetic tunnel junctions （MTJs）. Our quantitative studies demonstrate rich bias dependence of STT and tunnel inagneto resistance （TMR） behaviors with respect to the interface roughness. Thermoelectric effects in Fe/Vac/Fe MTJs is remarkable. We observe larger ZT of 6.2 in 8 ML clean Vacuum barrier, where responsible for. Thermo-STT in Fe/Vac/Fe with similar barrier thickness. the heavily restraitmd thermal conductance should be MTJs show same order as that in Fe/MgO/Fe MTJs with similar barrier thickness.
