Magnetic skyrmions are recognized as potential information carriers for building the next-generation spintronic memory and logic devices.Towards functional device applications,efficient electrical detection of skyrmio...Magnetic skyrmions are recognized as potential information carriers for building the next-generation spintronic memory and logic devices.Towards functional device applications,efficient electrical detection of skyrmions at room temperature is one of the most important prerequisites.展开更多
Low frequency noise has been investigated at room temperature for asymmetric double barrier magnetic tunnel junctions（DBMTJs）, where the coupling between the top and middle CoFeB layers is antiferromagnetic with a 0...Low frequency noise has been investigated at room temperature for asymmetric double barrier magnetic tunnel junctions（DBMTJs）, where the coupling between the top and middle CoFeB layers is antiferromagnetic with a 0.8-nm thin top Mg O barrier of the CoFeB/MgO/CoFe/CoFeB/MgO/CoFe B DBMTJ. At enough large bias, 1/f noise dominates the voltage noise power spectra in the low frequency region, and is conventionally characterized by the Hooge parameter αmag.With increasing external field, the top and bottom ferromagnetic layers are aligned by the field, and then the middle free layer rotates from antiparallel state（antiferromagnetic coupling between top and middle ferromagnetic layers） to parallel state. In this rotation process αmag and magnetoresistance-sensitivity-product show a linear dependence, consistent with the fluctuation dissipation relation. With the magnetic field applied at different angles（θ） to the easy axis of the free layer,the linear dependence persists while the intercept of the linear fit satisfies a cos（θ） dependence, similar to that for the magnetoresistance, suggesting intrinsic relation between magnetic losses and magnetoresistance.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
To study the influence of CoFeB/MgO interface on tunneling magnetoresistance （TMR）, different structures of magnetic tunnel junctions （MTJs） are successfully prepared by the magnetron sputtering technique and char...To study the influence of CoFeB/MgO interface on tunneling magnetoresistance （TMR）, different structures of magnetic tunnel junctions （MTJs） are successfully prepared by the magnetron sputtering technique and characterized by atomic force microscopy, a physical property measurement system, x-ray photoelectron spectroscopy, and transmission electron microscopy. The experimental results show that TMR of the CoFeB/Mg/MgO/CoFeB structure is evidently improved in comparison with the CoFeB/MgO/CoFeB structure because the inserted Mg layer prevents Fe-oxide formation at the CoFeB/MgO interface, which occurs in CoFeB/MgO/CoFeB MTJs. The inherent properties of the CoFeB/MgO/CoFeB, CoFeB/Fe-oxide/MgO/CoFeB and CoFeB/Mg/MgO/CoFeB MTJs are simulated by using the theories of density functions and non-equilibrium Green functions. The simulated results demonstrate that TMR of CoFeB/Fe-oxide/MgO/CoFeB MTJs is severely decreased and is only half the value of the CoFeB/Mg/MgO/CoFeB MTJs. Based on the experimental results and theoretical analysis, it is believed that in CoFeB/MgO/CoFeB MTJs, the interface oxidation of the CoFeB layer is the main reason to cause a remarkable reduction of TMR, and the inserted Mg layer may play an important role in protecting Fe atoms from oxidation, and then increasing TMR.展开更多
Temperature dependence of tunnel magnetoresistance (TMR) ratio, resistance, and coercivity from 4.2 K to room temperature (RT), applied de bias voltage dependence of the TMR ratio and resistances at 4.2 K and RT, tunn...Temperature dependence of tunnel magnetoresistance (TMR) ratio, resistance, and coercivity from 4.2 K to room temperature (RT), applied de bias voltage dependence of the TMR ratio and resistances at 4.2 K and RT, tunnel current I and dynamic conductance dI/dV as functions of the de bias voltage at 4.2 K, and inelastic electron tunneling (IET) spectroscopy, d(2)I/dV(2) versus V, at 4.2 K for a tunnel junction of Ta(5 nm)/Ni79Fe21(25 nm)/Ir22Mn78(12 nm)/Co75Fe25(4 nm)/Al(0.8 nm)-oxide/Co75Fe25(4 nm)/Ni79Fe21(25 nm)/Ta(5 nm) were systematically investigated. High TMR ratio of 59.2% at 4.2 K and 41.3% at RT were observed for this junction after annealing at 275 degreesC for an hour. The temperature dependence of TMR ratio and resistances from 4.2 to 300 K at 1.0 mV bias and the de bias voltage dependence of TMR ratio at 4.2 K from 0 to 80 mV can be evaluated by a comparison of self-consistent calculations with the experimental data based on the magnon-assisted inelastic excitation model and theory. An anisotropic wavelength cutoff energy of spin-wave spectrum in magnetic tunnel junctions (MTJs) was suggested, which is necessary for self-consistent calculations, based on a series of IET spectra observed in the MTJs.展开更多
In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlOx/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization pro...In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlOx/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants.展开更多
Tantalum as an insulating barrier can take the place of Al in magnetic tunnel junctions (MTJs). Ta barriers in MTJs were fabricated by natural oxidation. X-ray photoelectron spectroscopy (XPS) was used to characterize...Tantalum as an insulating barrier can take the place of Al in magnetic tunnel junctions (MTJs). Ta barriers in MTJs were fabricated by natural oxidation. X-ray photoelectron spectroscopy (XPS) was used to characterize the oxidation states of Ta barrier. The experimental results show that the chemical state of tantalum is pure Ta^(5+) and the thickness of the oxide is 1.3 nm. The unoxidized Ta in the barrier may chemically reacted with NiFe layer which is usually used in MTJs to form an intermetallic compound, NiTa_2. A magnetic 'dead layer' could be produced in the NiFe/Ta interface. The 'dead layer' is likely to influence the spinning electron transport and the magnetoresistance effect.展开更多
Tantalum as an insulating barrier can take the place of Al in magnetic tunneljunctions (MTJs). Ta barriers in MTJs were fabricated by natural oxidation. X-ray photoelectronspectroscopy (XPS) was used to characterize t...Tantalum as an insulating barrier can take the place of Al in magnetic tunneljunctions (MTJs). Ta barriers in MTJs were fabricated by natural oxidation. X-ray photoelectronspectroscopy (XPS) was used to characterize the oxidation states of Ta barrier. The experimentalresults show that the chemical state of tantalum is pure Ta^(5+) and the thickness of the oxide is1.3 nm. The unoxidized Ta in the barrier may chemically reacted with NiFe layer which is usuallyused in MTJs to form an intermetallic compound, NiTa_2. A magnetic 'dead layer' could be produced inthe NiFe/Ta interface. The 'dead layer' is likely to influence the spinning electron transport andthe magnetoresistance effect.展开更多
We investigate bias and different barrier thicknesses effects on quantities related to spin and charge currents in MgO-based magnetic tunnel junctions. Using the non-Equilibrium Green＇s function formalism, we demonst...We investigate bias and different barrier thicknesses effects on quantities related to spin and charge currents in MgO-based magnetic tunnel junctions. Using the non-Equilibrium Green＇s function formalism, we demonstrate that the in-plane and out-of-plane components of the spin-transfer torque have asymmetric and symmetric behaviors respectively. Magneto-resistance also decreases with increasing barrier thickness. The Landau–Lifshits–Gilbert equation describes the dynamics of the magnetization made by spin transfer torque. Increasing in spin current above its critical value or smaller the magnet reduces the switching time which is major result for making of new memory devices.展开更多
An explicit function expression for the bias voltage or/and temperature dependences of tunnel magnetoresistance ratio and resistances were obtained with a unique set of intrinsic parameters. Two of these intrinsic par...An explicit function expression for the bias voltage or/and temperature dependences of tunnel magnetoresistance ratio and resistances were obtained with a unique set of intrinsic parameters. Two of these intrinsic parameters are the Curie temperature TC and the density of state (DOS) for itinerant majority and minority electrons ξ(ρM/ρm), which are the eigen parameters of ferromagnetic electrodes. Others are the spin-dependent matrix-element ratio (i.e., |Td|2/|TJ|2 ) and the anisotropic-wavelength-cutoff energy ECγ of spin-wave spectrum in magnetic tunnel junction (MTJ), which are the structure parameters of an MTJ. These intrinsic parameters can be predetermined using the experimental measurement or, in principle, using the first-principle calculation method for an MTJ with the three key layers of FM/I/FM. Furthermore, a series of experimental data for an MTJ, for example, a spin-valve-type MTJ of Ta (5 nm)/Ni79Fe21(25 nm)/lr22Mn78(12 nm)/Co75Fe25(4 nm)/AI(0.8 nm)-oxide/Co75Fe25(4 nm)/Ni79Fe21(20 nm)/Ta (5 nm) in this work, can be self-consistently evaluated and explained using such concise explicit function formulations.展开更多
In biological neural systems,noise is ubiquitous but does not affect the correct decisions made in the complex cognitive tasks.Decision-making in biological neural system is typically achieved by accumulating input in...In biological neural systems,noise is ubiquitous but does not affect the correct decisions made in the complex cognitive tasks.Decision-making in biological neural system is typically achieved by accumulating input information over a period of time.Inspired by recent developments in neurosciences,we design a decision-making module based on spintronic devices,utilizing superparamagnetic tunnel junctions as artificial neurons.The feasibility of this decision-making module is verified through circuit simulations.Taking a multi-layer perceptron as an example,the module significantly improves the accuracy of the perceptron in the handwritten digit recognition task.Furthermore,the spintronic decision-making module offers advantages over the conventional pooling methods,such as adaptive decision time,high performance and the absence of analog-to-digital conversion.The decision-making module is flexible to be integrated into artificial neural networks and provides a general yet effective solution to enhance performance against device noise.展开更多
With RF sputtering process, Si/Si02/Ta/Ru/Ta/CoFeB/MgO/CoFeB/Ta/Ru structure has been grown on Si （100） substrate. Attempting different targets and adjusting the oxygen dose, the crystallization quality of the MgO l...With RF sputtering process, Si/Si02/Ta/Ru/Ta/CoFeB/MgO/CoFeB/Ta/Ru structure has been grown on Si （100） substrate. Attempting different targets and adjusting the oxygen dose, the crystallization quality of the MgO layer is studied. The X-ray diffraction measurements demonstrate that crystal structure and crystallization quality of MgO layers are related to the type of target and concentration of oxygen in sputtering process. With the method sputtering Mg in an ambient flow of oxygen, not only the crystallization quality of a normal MgO layer with lattice constant of 0.421 nm is improved, but also a new MgO crystal with lattice constant of 0.812 nm is formed and the perpendicular magnetic anisotropy of CoFeB is enhanced. Also it is found that crystallization quality for both the normal MgO and new MgO is more improved with MgO target and same oxygen dose, which means that this new method is helpful to form a new structure of MgO annealed at 400 ℃ in vacuum. with lattice constant of 0.812 nm. All of the samples were展开更多
Magnetic droplets,a class of highly nonlinear magnetodynamic solitons,can be nucleated and stabilized in nanocontact spintorque nano-oscillators.Here we experimentally demonstrate magnetic droplets in magnetic tunnel ...Magnetic droplets,a class of highly nonlinear magnetodynamic solitons,can be nucleated and stabilized in nanocontact spintorque nano-oscillators.Here we experimentally demonstrate magnetic droplets in magnetic tunnel junctions(MTJs).The droplet nucleation is accompanied by power enhancement compared with its ferromagnetic resonance modes.The nucleation and stabilization of droplets are ascribed to the double-Co Fe B free-layer structure in the all-perpendicular MTJ,which provides a low Zhang-Li torque and a high pinning field.Our results enable better electrical sensitivity in fundamental studies of droplets and show that the droplets can be utilized in MTJ-based applications and materials science.展开更多
Spintronics has received a great attention and significant interest within the past decades,and provided considerable and remarked applications in industry and electronic information etc.In spintronics,the MgO based m...Spintronics has received a great attention and significant interest within the past decades,and provided considerable and remarked applications in industry and electronic information etc.In spintronics,the MgO based magnetic tunnel junction(MTJ) is an important research advancement because of its physical properties and excellent performance,such as the high TMR ratio in MgO based MTJs.We present an overview of more than a decade development in MgO based MTJs.The review contains three main sections.(1) Research of several types of MgO based MTJs,including single-crystal MgO barrier based-MTJs,double barrier MTJs,MgO based MTJs with interlayer,novel electrode material MTJs based on MgO,novel barrier based MTJs,novel barrier MTJs based on MgO,and perpendicular MTJs.(2) Some typical physical effects in MgO based MTJs,which include six observed physical effects in MgO based MTJs,namely spin transfer torque(STT) effect,Coulomb blockade magnetoresistance(CBMR) effect,oscillatory magnetoresistance,quantum-well resonance tunneling effect,electric field assisted magnetization switching effect,and spincaloric effect.(3) In the last section,a brief introduction of some important device applications of MgO based MTJs,such as GMR & TMR read heads and magneto-sensitive sensors,both field and current switching MRAM,spin nano oscillators,and spin logic devices,have been provided.展开更多
A brief review is presented,which includes the direct current,alternate current,electrical and thermoelectrical transport as well as spin transfer effect in a variety of spin-based nanostructures such as the magnetic ...A brief review is presented,which includes the direct current,alternate current,electrical and thermoelectrical transport as well as spin transfer effect in a variety of spin-based nanostructures such as the magnetic tunnel junction(MTJ),ferromagnet(FM)-quantum dot(QD)/FM-FM,double barrier MTJ,FM-marginal Fermi liquid-FM,FM-unconventional superconductor-FM(FUSF),quantum ring and optical spin-field-effect transistor.The magnetoresistances in those structures,spin accumulation effect in FM-QD-FM and FUSF systems,spin injection and spin filter into semiconductor,spin transfer effect,photon-assisted spin transport,magnonassisted tunneling,electron-electron interaction effect on spin transport,laser-controlled spin dynamics,and thermoelectrical spin transport are discussed.展开更多
Magnetic tunnel junctions(MTJs)switched by spin-orbit torque(SOT)have attracted substantial interest owing to their advantages of ultrahigh speed and prolonged endurance.Both field-free magnetization switching and hig...Magnetic tunnel junctions(MTJs)switched by spin-orbit torque(SOT)have attracted substantial interest owing to their advantages of ultrahigh speed and prolonged endurance.Both field-free magnetization switching and high tunneling magnetoresistance(TMR)are critical for the practical application of SOT magnetic random access memory(MRAM).In this work,we propose an MTJ structure based on an iridium(Ir)bottom layer.Ir metal is a desirable candidate for field-free SOT switching owing to its strong intrinsic spin Hall conductivity(SHC),which can be enhanced via doping.Herein,we study TMR in Ir-based MTJs with symmetric and asymmetric structures.Ir-based MTJs exhibit large TMR,which can be further enhanced by heavy metal symmetry owing to the resonant tunneling effect.Our comprehensive investigations illustrate that Ir-based MTJs are promising candidates for realizing SOT switching and high TMR.展开更多
Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni79Fe21(5)/Ir22 Mn78(12)/Co60Fe20B20(4)/Al(0.8)-oxide/Co60Fe20B20(4)/Cu(30)/Ta(5) [thickness unit: nm] using the amorphou...Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni79Fe21(5)/Ir22 Mn78(12)/Co60Fe20B20(4)/Al(0.8)-oxide/Co60Fe20B20(4)/Cu(30)/Ta(5) [thickness unit: nm] using the amorphous Co60Fe20B20 alloy as free and pinned layers were micro-fabricated. The experimental investigations showed that the tunnel magnetoresistance (TMR) ratio and the resistance decrease with increasing dc bias voltage from 0 to 500 mV or with increasing temperature from 4.2 K to RT. A high TMR ratio of 86.2% at 4.2 K, which corresponds to the high spin polarization of Co60Fe20B20, 55%, was observed in the MTJs after annealing at 270℃ for 1 h. High TMR ratio of 53.1%, low junction resistance-area product RS of 3.56 kΩμm2, small coercivity HC of ≤4 Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V1/2 of greater than 570 mV at RT have been achieved in such Co-Fe-B MTJs.展开更多
We present theoretical calculations of spin transport in spin filtering magnetic tunnelling junctions based on the Landauer Biittiker formalism and taking into account the spin-orbit coupling （SOC）. It is shown that...We present theoretical calculations of spin transport in spin filtering magnetic tunnelling junctions based on the Landauer Biittiker formalism and taking into account the spin-orbit coupling （SOC）. It is shown that spin-flip scattering induced by SOC is stronger in parallel alignment of magnetization of the ferromegnet barrier （FB） and the ferromagnetic electrode than that in antiparallel case. The increase of negative tunnelling magnetoresistance with bias is in agreement with recent experimental observation.展开更多
We investigate properties of perpendicular anisotropy magnetic tunnel junctions(pMTJs) with a stack structure MgO/CoFeB/Ta/CoFeB/MgO as the free layer(or recording layer),and obtain the necessary device parameters fro...We investigate properties of perpendicular anisotropy magnetic tunnel junctions(pMTJs) with a stack structure MgO/CoFeB/Ta/CoFeB/MgO as the free layer(or recording layer),and obtain the necessary device parameters from the tunneling magnetoresistance(TMR) vs.field loops and current-driven magnetization switching experiments.Based on the experimental results and device parameters,we further estimate current-driven switching performance of pMTJ including switching time and power,and their dependence on perpendicular magnetic anisotropy and damping constant of the free layer by SPICE-based circuit simulations.Our results show that the pMTJ cells exhibit a less than 1 ns switching time and write energies <1.4 pJ;meanwhile the lower perpendicular magnetic anisotropy(PMA) and damping constant can further reduce the switching time at the studied range of damping constant α <0.1.Additionally,our results demonstrate that the pMTJs with the thermal stability factor■73 can be easily transformed into spin-torque nano-oscillators from magnetic memory as microwave sources or detectors for telecommunication devices.展开更多
Magnetic tunnel junctions(MTJs) based on MgO barrier have been fabricated by sputtering single crystal MgO target and metal Mg target, respectively, using magnetic sputtering system Nordiko 2000. MgO barriers have bee...Magnetic tunnel junctions(MTJs) based on MgO barrier have been fabricated by sputtering single crystal MgO target and metal Mg target, respectively, using magnetic sputtering system Nordiko 2000. MgO barriers have been formed by a multi-step deposition and natural oxidization of Mg layer. Mg layer thickness,oxygen flow rate and oxidization time were adjusted and the tunnel magnetoresistance(TMR) ratio of optimal MTJs is over 60% at annealing temperature 385. The(001) MgO crystal structure was obtained when the separation distance between MgO target and substrate is less than 6 cm. The TMR ratio of most MgO based MTJs are over 100% at the separation distance of 5 cm and annealing temperature 340. The TMR ratios of MTJs are almost zero when the separation distance ranges from 6 to 10 cm, due to the amorphous nature of the MgO film.展开更多
基金supported by the National Key R&D Program of China(Grant No.2022YFA1405100)the NSFC distinguished Young Scholar program(Grant No.12225409)+6 种基金the Basic Science Center Project of National Natural Science Foundation of China(NSFC)(Grant No.52388201)the NSFC general program(Grant Nos.52271181,51831005,and 12421004)the Innovation Program for Quantum Science and Technology(Grant No.2023ZD0300500)Beijing Natural Science Foundation(Grant No.Z240006)supported by the KAUST Office of Sponsored Research(OSR)under Award Nos.ORA-CRG102021-4665 and ORA-CRG11-2022-5031supported by the National Key Research and Development Program of China(No.2024YFA1408503)Sichuan Province Science and Technology Support Program(No.2025YFHZ0147)。
文摘Magnetic skyrmions are recognized as potential information carriers for building the next-generation spintronic memory and logic devices.Towards functional device applications,efficient electrical detection of skyrmions at room temperature is one of the most important prerequisites.
基金supported by the National Basic Research Program of China(Grant Nos.2011CBA00106,2012CB927400,2010CB934401,and 2014AA032904)the National High Technology Research and Development Program of China(Grant No.2014AA032904)the National Natural Science Foundation of China(Grant Nos.11434014 and 11104252)
文摘Low frequency noise has been investigated at room temperature for asymmetric double barrier magnetic tunnel junctions（DBMTJs）, where the coupling between the top and middle CoFeB layers is antiferromagnetic with a 0.8-nm thin top Mg O barrier of the CoFeB/MgO/CoFe/CoFeB/MgO/CoFe B DBMTJ. At enough large bias, 1/f noise dominates the voltage noise power spectra in the low frequency region, and is conventionally characterized by the Hooge parameter αmag.With increasing external field, the top and bottom ferromagnetic layers are aligned by the field, and then the middle free layer rotates from antiparallel state（antiferromagnetic coupling between top and middle ferromagnetic layers） to parallel state. In this rotation process αmag and magnetoresistance-sensitivity-product show a linear dependence, consistent with the fluctuation dissipation relation. With the magnetic field applied at different angles（θ） to the easy axis of the free layer,the linear dependence persists while the intercept of the linear fit satisfies a cos（θ） dependence, similar to that for the magnetoresistance, suggesting intrinsic relation between magnetic losses and magnetoresistance.
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 National Defense Advance Research Foundation under Grant No 9140A08XXXXXX0DZ106the Basic Research Program of Ministry of Education of China under Grant No JY10000925005+2 种基金the Scientific Research Program Funded by Shaanxi Provincial Education Department under Grant No 11JK0912the Scientific Research Foundation of Xi'an University of Science and Technology under Grant No 2010011the Doctoral Research Startup Fund of Xi'an University of Science and Technology under Grant No 2010QDJ029
文摘To study the influence of CoFeB/MgO interface on tunneling magnetoresistance （TMR）, different structures of magnetic tunnel junctions （MTJs） are successfully prepared by the magnetron sputtering technique and characterized by atomic force microscopy, a physical property measurement system, x-ray photoelectron spectroscopy, and transmission electron microscopy. The experimental results show that TMR of the CoFeB/Mg/MgO/CoFeB structure is evidently improved in comparison with the CoFeB/MgO/CoFeB structure because the inserted Mg layer prevents Fe-oxide formation at the CoFeB/MgO interface, which occurs in CoFeB/MgO/CoFeB MTJs. The inherent properties of the CoFeB/MgO/CoFeB, CoFeB/Fe-oxide/MgO/CoFeB and CoFeB/Mg/MgO/CoFeB MTJs are simulated by using the theories of density functions and non-equilibrium Green functions. The simulated results demonstrate that TMR of CoFeB/Fe-oxide/MgO/CoFeB MTJs is severely decreased and is only half the value of the CoFeB/Mg/MgO/CoFeB MTJs. Based on the experimental results and theoretical analysis, it is believed that in CoFeB/MgO/CoFeB MTJs, the interface oxidation of the CoFeB layer is the main reason to cause a remarkable reduction of TMR, and the inserted Mg layer may play an important role in protecting Fe atoms from oxidation, and then increasing TMR.
文摘Temperature dependence of tunnel magnetoresistance (TMR) ratio, resistance, and coercivity from 4.2 K to room temperature (RT), applied de bias voltage dependence of the TMR ratio and resistances at 4.2 K and RT, tunnel current I and dynamic conductance dI/dV as functions of the de bias voltage at 4.2 K, and inelastic electron tunneling (IET) spectroscopy, d(2)I/dV(2) versus V, at 4.2 K for a tunnel junction of Ta(5 nm)/Ni79Fe21(25 nm)/Ir22Mn78(12 nm)/Co75Fe25(4 nm)/Al(0.8 nm)-oxide/Co75Fe25(4 nm)/Ni79Fe21(25 nm)/Ta(5 nm) were systematically investigated. High TMR ratio of 59.2% at 4.2 K and 41.3% at RT were observed for this junction after annealing at 275 degreesC for an hour. The temperature dependence of TMR ratio and resistances from 4.2 to 300 K at 1.0 mV bias and the de bias voltage dependence of TMR ratio at 4.2 K from 0 to 80 mV can be evaluated by a comparison of self-consistent calculations with the experimental data based on the magnon-assisted inelastic excitation model and theory. An anisotropic wavelength cutoff energy of spin-wave spectrum in magnetic tunnel junctions (MTJs) was suggested, which is necessary for self-consistent calculations, based on a series of IET spectra observed in the MTJs.
基金supported by the National Natural Science Foundation of China (Grant No 50671048)
文摘In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlOx/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants.
文摘Tantalum as an insulating barrier can take the place of Al in magnetic tunnel junctions (MTJs). Ta barriers in MTJs were fabricated by natural oxidation. X-ray photoelectron spectroscopy (XPS) was used to characterize the oxidation states of Ta barrier. The experimental results show that the chemical state of tantalum is pure Ta^(5+) and the thickness of the oxide is 1.3 nm. The unoxidized Ta in the barrier may chemically reacted with NiFe layer which is usually used in MTJs to form an intermetallic compound, NiTa_2. A magnetic 'dead layer' could be produced in the NiFe/Ta interface. The 'dead layer' is likely to influence the spinning electron transport and the magnetoresistance effect.
基金This work was financially supported by the National Natural Science Foundation of China and the Research Foundation for the Doctoral Program of Higher Education of China under Grant No.50271007 and 20030008003, respectively
文摘Tantalum as an insulating barrier can take the place of Al in magnetic tunneljunctions (MTJs). Ta barriers in MTJs were fabricated by natural oxidation. X-ray photoelectronspectroscopy (XPS) was used to characterize the oxidation states of Ta barrier. The experimentalresults show that the chemical state of tantalum is pure Ta^(5+) and the thickness of the oxide is1.3 nm. The unoxidized Ta in the barrier may chemically reacted with NiFe layer which is usuallyused in MTJs to form an intermetallic compound, NiTa_2. A magnetic 'dead layer' could be produced inthe NiFe/Ta interface. The 'dead layer' is likely to influence the spinning electron transport andthe magnetoresistance effect.
文摘We investigate bias and different barrier thicknesses effects on quantities related to spin and charge currents in MgO-based magnetic tunnel junctions. Using the non-Equilibrium Green＇s function formalism, we demonstrate that the in-plane and out-of-plane components of the spin-transfer torque have asymmetric and symmetric behaviors respectively. Magneto-resistance also decreases with increasing barrier thickness. The Landau–Lifshits–Gilbert equation describes the dynamics of the magnetization made by spin transfer torque. Increasing in spin current above its critical value or smaller the magnet reduces the switching time which is major result for making of new memory devices.
基金This work was supported by 2000 Hundred Talents Program project of Chinese Academy of Sciences and 973 project with Grant No. 2001CB610601 of PRC Ministry of Science and Technology. X.F.Han also gratefully acknowledges the partial support of K.C.Wong Edu
文摘An explicit function expression for the bias voltage or/and temperature dependences of tunnel magnetoresistance ratio and resistances were obtained with a unique set of intrinsic parameters. Two of these intrinsic parameters are the Curie temperature TC and the density of state (DOS) for itinerant majority and minority electrons ξ(ρM/ρm), which are the eigen parameters of ferromagnetic electrodes. Others are the spin-dependent matrix-element ratio (i.e., |Td|2/|TJ|2 ) and the anisotropic-wavelength-cutoff energy ECγ of spin-wave spectrum in magnetic tunnel junction (MTJ), which are the structure parameters of an MTJ. These intrinsic parameters can be predetermined using the experimental measurement or, in principle, using the first-principle calculation method for an MTJ with the three key layers of FM/I/FM. Furthermore, a series of experimental data for an MTJ, for example, a spin-valve-type MTJ of Ta (5 nm)/Ni79Fe21(25 nm)/lr22Mn78(12 nm)/Co75Fe25(4 nm)/AI(0.8 nm)-oxide/Co75Fe25(4 nm)/Ni79Fe21(20 nm)/Ta (5 nm) in this work, can be self-consistently evaluated and explained using such concise explicit function formulations.
基金supported by the National Natural Science Foundation of China(Grant No.12174028)。
文摘In biological neural systems,noise is ubiquitous but does not affect the correct decisions made in the complex cognitive tasks.Decision-making in biological neural system is typically achieved by accumulating input information over a period of time.Inspired by recent developments in neurosciences,we design a decision-making module based on spintronic devices,utilizing superparamagnetic tunnel junctions as artificial neurons.The feasibility of this decision-making module is verified through circuit simulations.Taking a multi-layer perceptron as an example,the module significantly improves the accuracy of the perceptron in the handwritten digit recognition task.Furthermore,the spintronic decision-making module offers advantages over the conventional pooling methods,such as adaptive decision time,high performance and the absence of analog-to-digital conversion.The decision-making module is flexible to be integrated into artificial neural networks and provides a general yet effective solution to enhance performance against device noise.
基金Project supported by the National Defense Advance Research Foundation(No.9140A080040410DZ106)the Basic Research Program of Ministry of Education,China(No.JY10000925005)+2 种基金the Scientific Research Program Funded by Shaanxi Provincial Education Department(No.11JK0912)the Scientific Research Foundation of Xi’an University of Science and Technology(No.2010011)the Doctoral Research Startup Fund of Xi’an University of Science and Technology(No.2010QDJ029)
文摘With RF sputtering process, Si/Si02/Ta/Ru/Ta/CoFeB/MgO/CoFeB/Ta/Ru structure has been grown on Si （100） substrate. Attempting different targets and adjusting the oxygen dose, the crystallization quality of the MgO layer is studied. The X-ray diffraction measurements demonstrate that crystal structure and crystallization quality of MgO layers are related to the type of target and concentration of oxygen in sputtering process. With the method sputtering Mg in an ambient flow of oxygen, not only the crystallization quality of a normal MgO layer with lattice constant of 0.421 nm is improved, but also a new MgO crystal with lattice constant of 0.812 nm is formed and the perpendicular magnetic anisotropy of CoFeB is enhanced. Also it is found that crystallization quality for both the normal MgO and new MgO is more improved with MgO target and same oxygen dose, which means that this new method is helpful to form a new structure of MgO annealed at 400 ℃ in vacuum. with lattice constant of 0.812 nm. All of the samples were
基金supported by the Beijing Municipal Science and Technology Project(Grant No.Z201100004220002)the National Natural Science Foundation of China(Grant Nos.61627813,61904009)the China Postdoctoral Science Foundation Funded Project(Grant No.2018M641151)。
文摘Magnetic droplets,a class of highly nonlinear magnetodynamic solitons,can be nucleated and stabilized in nanocontact spintorque nano-oscillators.Here we experimentally demonstrate magnetic droplets in magnetic tunnel junctions(MTJs).The droplet nucleation is accompanied by power enhancement compared with its ferromagnetic resonance modes.The nucleation and stabilization of droplets are ascribed to the double-Co Fe B free-layer structure in the all-perpendicular MTJ,which provides a low Zhang-Li torque and a high pinning field.Our results enable better electrical sensitivity in fundamental studies of droplets and show that the droplets can be utilized in MTJ-based applications and materials science.
基金supported by the State Key Project of Fundamental Research of the Ministry of Science and Technology(Grant No. 2010CB934400)the National Natural Science Foundation of China (Grant Nos.10934099,51021061,and 11104338)+2 种基金the National Science Fund for Distinguished Young Scholars(Grant No.50325104)the International Collaborative Research Programs between NSFC and EPSRC of the United Kingdom(Grant No.10911130234)between NSFC and ANR of France(Grant No.F040803)
文摘Spintronics has received a great attention and significant interest within the past decades,and provided considerable and remarked applications in industry and electronic information etc.In spintronics,the MgO based magnetic tunnel junction(MTJ) is an important research advancement because of its physical properties and excellent performance,such as the high TMR ratio in MgO based MTJs.We present an overview of more than a decade development in MgO based MTJs.The review contains three main sections.(1) Research of several types of MgO based MTJs,including single-crystal MgO barrier based-MTJs,double barrier MTJs,MgO based MTJs with interlayer,novel electrode material MTJs based on MgO,novel barrier based MTJs,novel barrier MTJs based on MgO,and perpendicular MTJs.(2) Some typical physical effects in MgO based MTJs,which include six observed physical effects in MgO based MTJs,namely spin transfer torque(STT) effect,Coulomb blockade magnetoresistance(CBMR) effect,oscillatory magnetoresistance,quantum-well resonance tunneling effect,electric field assisted magnetization switching effect,and spincaloric effect.(3) In the last section,a brief introduction of some important device applications of MgO based MTJs,such as GMR & TMR read heads and magneto-sensitive sensors,both field and current switching MRAM,spin nano oscillators,and spin logic devices,have been provided.
基金supported in part by the National Science Fund for Distinguished Young Scholars of China(Grant No. 10625419)the National Natural Science Foundation of China(Grant Nos. 90922033 and 10934008)+1 种基金the Ministry of Science and Technology of China (Grant Nos.2012CB932900 and 2013CB933401)the Chinese Academy of Sciences,China,the DFG and the state of Saxony-Anhalt,Germany
文摘A brief review is presented,which includes the direct current,alternate current,electrical and thermoelectrical transport as well as spin transfer effect in a variety of spin-based nanostructures such as the magnetic tunnel junction(MTJ),ferromagnet(FM)-quantum dot(QD)/FM-FM,double barrier MTJ,FM-marginal Fermi liquid-FM,FM-unconventional superconductor-FM(FUSF),quantum ring and optical spin-field-effect transistor.The magnetoresistances in those structures,spin accumulation effect in FM-QD-FM and FUSF systems,spin injection and spin filter into semiconductor,spin transfer effect,photon-assisted spin transport,magnonassisted tunneling,electron-electron interaction effect on spin transport,laser-controlled spin dynamics,and thermoelectrical spin transport are discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.61627813,and 61571023)the International Collaboration Project B16001,and the National Key Technology Program of China(Grant No.2017ZX01032101)supported by the Academic Excellence Foundation of BUAA for PhD Students
文摘Magnetic tunnel junctions(MTJs)switched by spin-orbit torque(SOT)have attracted substantial interest owing to their advantages of ultrahigh speed and prolonged endurance.Both field-free magnetization switching and high tunneling magnetoresistance(TMR)are critical for the practical application of SOT magnetic random access memory(MRAM).In this work,we propose an MTJ structure based on an iridium(Ir)bottom layer.Ir metal is a desirable candidate for field-free SOT switching owing to its strong intrinsic spin Hall conductivity(SHC),which can be enhanced via doping.Herein,we study TMR in Ir-based MTJs with symmetric and asymmetric structures.Ir-based MTJs exhibit large TMR,which can be further enhanced by heavy metal symmetry owing to the resonant tunneling effect.Our comprehensive investigations illustrate that Ir-based MTJs are promising candidates for realizing SOT switching and high TMR.
基金Project supported by the State Key Project of Fundamen-tal Research of Ministry of Science and Technology(MOST,China,Grant No.2001CB610601)Chinese Academy of Science.X.F.Han gratefully thanks the partial support of the National Natural Science Foundation of China(50271081 and 10274103)Distinct Young Researcher Foundation(50325104).
文摘Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni79Fe21(5)/Ir22 Mn78(12)/Co60Fe20B20(4)/Al(0.8)-oxide/Co60Fe20B20(4)/Cu(30)/Ta(5) [thickness unit: nm] using the amorphous Co60Fe20B20 alloy as free and pinned layers were micro-fabricated. The experimental investigations showed that the tunnel magnetoresistance (TMR) ratio and the resistance decrease with increasing dc bias voltage from 0 to 500 mV or with increasing temperature from 4.2 K to RT. A high TMR ratio of 86.2% at 4.2 K, which corresponds to the high spin polarization of Co60Fe20B20, 55%, was observed in the MTJs after annealing at 270℃ for 1 h. High TMR ratio of 53.1%, low junction resistance-area product RS of 3.56 kΩμm2, small coercivity HC of ≤4 Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V1/2 of greater than 570 mV at RT have been achieved in such Co-Fe-B MTJs.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10564004)Korea Research Foundation(Grant No. KRF-2005-070-C00065)
文摘We present theoretical calculations of spin transport in spin filtering magnetic tunnelling junctions based on the Landauer Biittiker formalism and taking into account the spin-orbit coupling （SOC）. It is shown that spin-flip scattering induced by SOC is stronger in parallel alignment of magnetization of the ferromegnet barrier （FB） and the ferromagnetic electrode than that in antiparallel case. The increase of negative tunnelling magnetoresistance with bias is in agreement with recent experimental observation.
基金Project supported by State Grid Corporation of China under the 2018 Science and Technology Project of State Grid Corporation:Research on electromagnetic measurement technology based on EIT and TMR(Grant No.JL71-18-007)。
文摘We investigate properties of perpendicular anisotropy magnetic tunnel junctions(pMTJs) with a stack structure MgO/CoFeB/Ta/CoFeB/MgO as the free layer(or recording layer),and obtain the necessary device parameters from the tunneling magnetoresistance(TMR) vs.field loops and current-driven magnetization switching experiments.Based on the experimental results and device parameters,we further estimate current-driven switching performance of pMTJ including switching time and power,and their dependence on perpendicular magnetic anisotropy and damping constant of the free layer by SPICE-based circuit simulations.Our results show that the pMTJ cells exhibit a less than 1 ns switching time and write energies <1.4 pJ;meanwhile the lower perpendicular magnetic anisotropy(PMA) and damping constant can further reduce the switching time at the studied range of damping constant α <0.1.Additionally,our results demonstrate that the pMTJs with the thermal stability factor■73 can be easily transformed into spin-torque nano-oscillators from magnetic memory as microwave sources or detectors for telecommunication devices.
基金Natural Science Foundation of Shanghai Science and Technology Commission (grant No. 11ZR1411300)Pujiang Talent Program of Shanghai Science and Technology Commission (grant No. 11PJ1402700) for the financial support
文摘Magnetic tunnel junctions(MTJs) based on MgO barrier have been fabricated by sputtering single crystal MgO target and metal Mg target, respectively, using magnetic sputtering system Nordiko 2000. MgO barriers have been formed by a multi-step deposition and natural oxidization of Mg layer. Mg layer thickness,oxygen flow rate and oxidization time were adjusted and the tunnel magnetoresistance(TMR) ratio of optimal MTJs is over 60% at annealing temperature 385. The(001) MgO crystal structure was obtained when the separation distance between MgO target and substrate is less than 6 cm. The TMR ratio of most MgO based MTJs are over 100% at the separation distance of 5 cm and annealing temperature 340. The TMR ratios of MTJs are almost zero when the separation distance ranges from 6 to 10 cm, due to the amorphous nature of the MgO film.
