In comparison to ferromagnets,antiferromagnets are believed to have superior advantages for applications in next-generation magnetic storage devices,including fast spin dynamics,vanishing stray fields and robust again...In comparison to ferromagnets,antiferromagnets are believed to have superior advantages for applications in next-generation magnetic storage devices,including fast spin dynamics,vanishing stray fields and robust against external magnetic field,etc.However,unlike ferromagnetic orders,which could be detected through tunneling magnetoresistance effect in magnetic tunnel junctions,the antiferromagnetic order(i.e.,Néel vector)cannot be effectively detected by the similar mechanism due to the spin degeneracy of conventional antiferromagnets.Recently discovered spin-splitting noncollinear antiferromagnets,such as Mn_(3)Pt with momentum-dependent spin polarization due to their special magnetic space group,make it possible to achieve remarkable tunneling magnetoresistance effects in noncollinear antiferromagnetic tunnel junctions.Through first-principles calculations,we demonstrate that the tunneling magnetoresistance ratio can reach more than 800% in Mn_(3)Pt/perovskite oxides/Mn_(3)Pt antiferromagnetic tunnel junctions.We also reveal the switching dynamics of Mn_(3)Pt thin film under magnetic fields using atomistic spin dynamic simulation.Our study provides a reliable method for detecting Néel vector of noncollinear antiferromagnets through the tunnel magnetoresistance effect and may pave its way for potential applications in antiferromagnetic memory devices.展开更多
Several critical clinical applications of magnetocardiography(MCG)involve its T wave.The T wave’s accuracy directly affects the diagnostic accuracy of MCG for ischemic heart disease and arrhythmogenic.Tunnel magnetor...Several critical clinical applications of magnetocardiography(MCG)involve its T wave.The T wave’s accuracy directly affects the diagnostic accuracy of MCG for ischemic heart disease and arrhythmogenic.Tunnel magnetoresistance(TMR)attracts attention as a new MCG measurement technique.However,the T waves measured by TMR are often drowned in noise.The accuracy of T waves needs to be discussed to determine the clinical value of MCG measured by TMR.This study uses an improved empirical mode decomposition(EMD)algorithm and averaging to eliminate the noise in the MCG measured by TMR.The MCG signals measured by TMR are compared with MCG measured by the optically pumped magnetometer(OPM)to judge its accuracy.Using the MCG measured by OPM as a reference,the relative errors in time and amplitude of the T wave measured by TMR are 3.4%and 1.8%,respectively.This is the first demonstration that TMR can accurately measure the time and amplitude of MCG T waves.The ability to provide reliable T wave data illustrates the significant clinical application value of TMR in MCG measurement.展开更多
Using the density functional theory and the nonequilibrium Green's function method, we studied the finite-bias quan- tum transport in a Cr/graphene/Cr magnetotunnel junction (MTJ) constructed by a single graphene l...Using the density functional theory and the nonequilibrium Green's function method, we studied the finite-bias quan- tum transport in a Cr/graphene/Cr magnetotunnel junction (MTJ) constructed by a single graphene layer sandwiched be- tween two semi-infinite Cr(111 ) electrodes. We found that the tunneling magnetoresistance (TMR) ratio in this MTJ reached 108%, which is close to that of a perfect spin filter. Under an external positive bias, we found that the TMR ratio remained constant at 65%, in contrast to MgO-based MTJs, the TMR ratios of which decrease with increasing bias. These results indicate that the Cr/graphene/Cr MTJ is a promising candidate for spintronics applications.展开更多
Spin-dependent transport in ferromagnet/organic-ferromagnet/metal junctions is investigated theoretically.The results reveal a large tunneling magnetoresistance up to 3230%by controlling the relative magnetization ori...Spin-dependent transport in ferromagnet/organic-ferromagnet/metal junctions is investigated theoretically.The results reveal a large tunneling magnetoresistance up to 3230%by controlling the relative magnetization orientation between the ferromagnet and the central organic ferromagnet.The mechanism is explained by distinct efficient spin-resolved tunneling states in the ferromagnet between the parallel and antiparallel spin configurations.The key role of the organic ferromagnet in generating the large magnetoresistance is explored,where the spin selection effect is found to enlarge the difference of the tunneling states between the parallel and antiparallel configurations by comparing with the conventional organic spin valves.The effects of intrinsic interactions in the organic ferromagnet including electron–lattice interaction and spin coupling with radicals on the magnetoresistance are discussed.This work demonstrates a promising potential of organic ferromagnets in the design of high-performance organic spin valves.展开更多
The transport property of electrons tunneling through arrays of magnetic and electric barriers is studied in silicene. In the tunneling transmission spectrum, the spin-valley-dependent filtered states can be achieved ...The transport property of electrons tunneling through arrays of magnetic and electric barriers is studied in silicene. In the tunneling transmission spectrum, the spin-valley-dependent filtered states can be achieved in an incident energy range which can be controlled by the electric gate voltage. For the parallel magnetization configuration, the transmission is asymmetric with respect to the incident angle θ, and electrons with a very large negative incident angle can always transmit in propagating modes for one of the spin-valley filtered states under a certain electromagnetic condition. But for the antiparallel configuration, the transmission is symmetric about θ and there is no such transmission channel. The difference of the transmission between the two configurations leads to a giant tunneling magnetoresistance (TMR) effect. The TMR can reach to 100% in a certain Fermi energy interval around the electrostatic potential. This energy interval can be adjusted significantly by the magnetic field and/or electric gate voltage. The results obtained may be useful for future valleytronic and spintronic applications, as well as magnetoresistance device based on silicene.展开更多
We investigate the tunneling magnetoresistance via δ doping in a graphei2e-based magnetic tunnel junction in detail. It is found that the transmission probability and the conductance oscillates with the position and...We investigate the tunneling magnetoresistance via δ doping in a graphei2e-based magnetic tunnel junction in detail. It is found that the transmission probability and the conductance oscillates with the position and the aptitude of the 8 doping. Also, both the transmission probability and the conductance at the paxallel configuration are suppressed by the magnetic field more obviously than that at the antiparallel configuration, which implies a large negative magnetoresistance for this device. The results show that the negative magnetoresistance of over 300% at B = 1.0 T is observed by choosing suitable doped parameters, and the temperature plays an important role in the magnetoresistance. Thus it is possible to open a way to effectively manipulate the magnetoresistance devices, and to make a type of magnetoresistance device by controlling the structural parameter of the δ doping.展开更多
Fe-O/AlO_x/Fe-O tunnel junctions were prepared by reactive magnetronsputtering under mixed working gas Ar+2 percent O_2. The insulating AlO_x layer of 1-2nm thicknesswas sputtered directly from A1_2O_3 target. Electro...Fe-O/AlO_x/Fe-O tunnel junctions were prepared by reactive magnetronsputtering under mixed working gas Ar+2 percent O_2. The insulating AlO_x layer of 1-2nm thicknesswas sputtered directly from A1_2O_3 target. Electrode layers were made of 80at. percent iron and20at. percent oxygen. Bottom Fe-O electrode deposited on glass substrate annealed at 473K at thepressure of 3 X 10^(-4) Pa for an hour shows disparate crystalline grain structure, lower electricalresistance and coercivity compared to the as-deposited top electrode. Only crystalline structrureof alpha-Fe is observed in both electrodes. Large tunnel magnetoresistance in large Fe-O/AlO_x/Fe-Ojunctions of 1cm^2 is observed at room temperature and the I-V characteristic curve of the junctionshows that the barrier of the junction is of high quality.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
Because of the wide selectivity of ferromagnetic and ferroelectric(FE)components,electric-field(E-field)control of magnetism via strain mediation can be easily realized through composite multiferroic heterostructures....Because of the wide selectivity of ferromagnetic and ferroelectric(FE)components,electric-field(E-field)control of magnetism via strain mediation can be easily realized through composite multiferroic heterostructures.Here,an MgO-based magnetic tunnel junction(MTJ)is chosen rationally as the ferromagnetic constitution and a high-activity(001)-Pb(Mg_(1/3)Nb_(2/3))_(0.7)Ti_(0.3)O_(3)(PMN-0.3PT)single crystal is selected as the FE component to create a multiferroic MTJ/FE hybrid structure.The shape of tunneling magnetoresistance(TMR)versus in situ E-fields imprints the butterfly loop of the piezo-strain of the FE without magnetic-field bias.The E-field-controlled change in the TMR ratio is up to-0.27%without magnetic-field bias.Moreover,when a typical magnetic field(~±10 Oe)is applied along the minor axis of the MTJ,the butterfly loop is changed significantly by the E-fields relative to that without magnetic-field bias.This suggests that the E-field-controlled junction resistance is spin-dependent and correlated with magnetization switching in the free layer of the MTJ.In addition,based on such a multiferroic heterostructure,a strain-gauge factor up to approximately 40 is achieved,which decreases further with a sign change from positive to negative with increasing magnetic fields.This multiferroic hybrid structure is a promising avenue to control TMR through E-fields in low-power-consumption spintronic and straintronic devices at room temperature.展开更多
We study the coutrol of gate voltage over the magnetization of a single-molecule magnet (SMM) weakly coupled to a ferromagnetic and a normal metal electrode in the presence of the temperature gradient between two el...We study the coutrol of gate voltage over the magnetization of a single-molecule magnet (SMM) weakly coupled to a ferromagnetic and a normal metal electrode in the presence of the temperature gradient between two electrodes. It is demonstrated that the SMM's magnetization can change periodically with periodic gate voltage due to the driving oI the temperature gradient. Under an appropriate matching of the electrode polarization, the temperature difference and the pulse width of gate voltage, the SMM's magnetization can be completely reversed in a period of gate voltage. The corresponding flipping time can be controlled by the system parameters. In addition, we also investigate the tunneling anisotropic magnetoresistance (TAMFt) of the device in the steady state when the ferromagnetic electrode is noncollinear with the easy axis of the SMM, and show the jump characteristic of the TAMR.展开更多
The tunneling conductance and tunneling magnetoresistance (TMR) are investigated inferromagnet/insulator/ferromagnet/insulator/d-wave superconductor (FM/I/FM/I/d-wave SC) structures by applyingan extended Blonder Tink...The tunneling conductance and tunneling magnetoresistance (TMR) are investigated inferromagnet/insulator/ferromagnet/insulator/d-wave superconductor (FM/I/FM/I/d-wave SC) structures by applyingan extended Blonder Tinkham-Klapwijk (BTK) approach. We study the effects of the exchange splitting in the FM,the magnetic impurity scattering in the thin insulator interface of FM/1/FM, and noncollinear magnetizations in adja-cent magnetic layers on the TMR. It is shown (1) that the tunneling conductance and TMR exhibit amplitude-varyingoscillating behavior with exchange splitting, (2) that with the presence of spin-flip scattering in insulator interface of FM/I/FM, the TMR can be dramatically enhanced, and (3) that the TMR depends strongly on the angle between themagnetization of two FMs.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
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 reported a study of tunnel magnetoresistance(TMR)effect in single manganite nanowire via the combination of magnetotransport and magnetic force microscopy imaging.TMR value up to 290%has been observed in single(La1...We reported a study of tunnel magnetoresistance(TMR)effect in single manganite nanowire via the combination of magnetotransport and magnetic force microscopy imaging.TMR value up to 290%has been observed in single(La1-yPry)1-x CaxMnO3 nanowires with varying width.We find that the TMR effect can be explained in the scenario of opening and blockade of conducting channels from inherent magnetic domain evolutions.Our findings provide a new route to fabricate TMR junctions and point towards future improvements in complex oxide-based TMR spintronics.展开更多
We investigate the spin-related currents and tunnel magnetoresistance through a quantum dot,which is side-coupled with a Majorana fermion zero mode and two thermal-driven ferromagnetic electrodes.It is found that the ...We investigate the spin-related currents and tunnel magnetoresistance through a quantum dot,which is side-coupled with a Majorana fermion zero mode and two thermal-driven ferromagnetic electrodes.It is found that the interplay of Majorana fermion and electrodes'spin polarization can induce a nonlinear thermal-bias spin current.This interplay also decreases the total magnitude of spin or charge current,in either parallel or antiparallel configuration.In addition,a thermal-driven negative tunnel magnetoresistance is found,which is an unique feature to characterize Majorana fermion.With large temperature difference,a step phenomenon is observed in gate tuned spin-up current.When the coupling between quantum dot and topological superconductor is strong enough,this step will evolve into a linear relation,revealing Majorana fermion's robustness.展开更多
Two-dimensional(2D) magnetic crystals have attracted great attention due to their emerging new physical phenomena. They provide ideal platforms to study the fundamental physics of magnetism in low dimensions. In this ...Two-dimensional(2D) magnetic crystals have attracted great attention due to their emerging new physical phenomena. They provide ideal platforms to study the fundamental physics of magnetism in low dimensions. In this research,magnetic tunneling junctions(MTJs) based on XSe2(X = Mn, V) with room-temperature ferromagnetism were studied using first-principles calculations. A large tunneling magnetoresistance(TMR) of 725.07% was obtained in the MTJs based on monolayer MnSe2. Several schemes were proposed to improve the TMR of these devices. Moreover, the results of our non-equilibrium transport calculations showed that the large TMR was maintained in these devices under a finite bias.The transmission spectrum was analyzed according to the orbital components and the electronic structure of the monolayer XSe2(X = Mn, V). The results in this paper demonstrated that the MTJs based on a 2D ferromagnet with room-temperature ferromagnetism exhibited reliable performance. Therefore, such devices show the possibility for potential applications in spintronics.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.T2394475,T2394470,and 12174129)。
文摘In comparison to ferromagnets,antiferromagnets are believed to have superior advantages for applications in next-generation magnetic storage devices,including fast spin dynamics,vanishing stray fields and robust against external magnetic field,etc.However,unlike ferromagnetic orders,which could be detected through tunneling magnetoresistance effect in magnetic tunnel junctions,the antiferromagnetic order(i.e.,Néel vector)cannot be effectively detected by the similar mechanism due to the spin degeneracy of conventional antiferromagnets.Recently discovered spin-splitting noncollinear antiferromagnets,such as Mn_(3)Pt with momentum-dependent spin polarization due to their special magnetic space group,make it possible to achieve remarkable tunneling magnetoresistance effects in noncollinear antiferromagnetic tunnel junctions.Through first-principles calculations,we demonstrate that the tunneling magnetoresistance ratio can reach more than 800% in Mn_(3)Pt/perovskite oxides/Mn_(3)Pt antiferromagnetic tunnel junctions.We also reveal the switching dynamics of Mn_(3)Pt thin film under magnetic fields using atomistic spin dynamic simulation.Our study provides a reliable method for detecting Néel vector of noncollinear antiferromagnets through the tunnel magnetoresistance effect and may pave its way for potential applications in antiferromagnetic memory devices.
基金supported by the Suzhou Tsinghua innovation leading action project(Grant No.2016SZ0217)the National Key Research and Development Program of China(Grant No.2016YFB0500902)。
文摘Several critical clinical applications of magnetocardiography(MCG)involve its T wave.The T wave’s accuracy directly affects the diagnostic accuracy of MCG for ischemic heart disease and arrhythmogenic.Tunnel magnetoresistance(TMR)attracts attention as a new MCG measurement technique.However,the T waves measured by TMR are often drowned in noise.The accuracy of T waves needs to be discussed to determine the clinical value of MCG measured by TMR.This study uses an improved empirical mode decomposition(EMD)algorithm and averaging to eliminate the noise in the MCG measured by TMR.The MCG signals measured by TMR are compared with MCG measured by the optically pumped magnetometer(OPM)to judge its accuracy.Using the MCG measured by OPM as a reference,the relative errors in time and amplitude of the T wave measured by TMR are 3.4%and 1.8%,respectively.This is the first demonstration that TMR can accurately measure the time and amplitude of MCG T waves.The ability to provide reliable T wave data illustrates the significant clinical application value of TMR in MCG measurement.
基金supported by the National Natural Science Foundation of China(Grant Nos.10874143,10974166,and 11574260)the Program for New Century Excellent Talents in University,China(Grant No.NCET-10-0169)+1 种基金the National Innovation Foundation for Graduate,China(Grant No.201310530003)the Computational Support from Shanghai Super-computer Center,China
文摘Using the density functional theory and the nonequilibrium Green's function method, we studied the finite-bias quan- tum transport in a Cr/graphene/Cr magnetotunnel junction (MTJ) constructed by a single graphene layer sandwiched be- tween two semi-infinite Cr(111 ) electrodes. We found that the tunneling magnetoresistance (TMR) ratio in this MTJ reached 108%, which is close to that of a perfect spin filter. Under an external positive bias, we found that the TMR ratio remained constant at 65%, in contrast to MgO-based MTJs, the TMR ratios of which decrease with increasing bias. These results indicate that the Cr/graphene/Cr MTJ is a promising candidate for spintronics applications.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974215,11704230,11674197,and 11874242)the Natural Science Foundation of Shandong Province,China(Grant No.ZR2019MA043)the Taishan Scholar Project of Shandong Province,China
文摘Spin-dependent transport in ferromagnet/organic-ferromagnet/metal junctions is investigated theoretically.The results reveal a large tunneling magnetoresistance up to 3230%by controlling the relative magnetization orientation between the ferromagnet and the central organic ferromagnet.The mechanism is explained by distinct efficient spin-resolved tunneling states in the ferromagnet between the parallel and antiparallel spin configurations.The key role of the organic ferromagnet in generating the large magnetoresistance is explored,where the spin selection effect is found to enlarge the difference of the tunneling states between the parallel and antiparallel configurations by comparing with the conventional organic spin valves.The effects of intrinsic interactions in the organic ferromagnet including electron–lattice interaction and spin coupling with radicals on the magnetoresistance are discussed.This work demonstrates a promising potential of organic ferromagnets in the design of high-performance organic spin valves.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11547249,51501102,and 11647157)the Science Foundation for Excellent Youth Doctors of Three Gorges University,China(Grant No.KJ2014B076)
文摘The transport property of electrons tunneling through arrays of magnetic and electric barriers is studied in silicene. In the tunneling transmission spectrum, the spin-valley-dependent filtered states can be achieved in an incident energy range which can be controlled by the electric gate voltage. For the parallel magnetization configuration, the transmission is asymmetric with respect to the incident angle θ, and electrons with a very large negative incident angle can always transmit in propagating modes for one of the spin-valley filtered states under a certain electromagnetic condition. But for the antiparallel configuration, the transmission is symmetric about θ and there is no such transmission channel. The difference of the transmission between the two configurations leads to a giant tunneling magnetoresistance (TMR) effect. The TMR can reach to 100% in a certain Fermi energy interval around the electrostatic potential. This energy interval can be adjusted significantly by the magnetic field and/or electric gate voltage. The results obtained may be useful for future valleytronic and spintronic applications, as well as magnetoresistance device based on silicene.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11447101 and 11447193the Youth Science Foundation of Guangxi Medical University of China under Grant No GXMUYSF201313the Guangxi Department of Education Research Projects of China under Grant No KY2015LX046
文摘We investigate the tunneling magnetoresistance via δ doping in a graphei2e-based magnetic tunnel junction in detail. It is found that the transmission probability and the conductance oscillates with the position and the aptitude of the 8 doping. Also, both the transmission probability and the conductance at the paxallel configuration are suppressed by the magnetic field more obviously than that at the antiparallel configuration, which implies a large negative magnetoresistance for this device. The results show that the negative magnetoresistance of over 300% at B = 1.0 T is observed by choosing suitable doped parameters, and the temperature plays an important role in the magnetoresistance. Thus it is possible to open a way to effectively manipulate the magnetoresistance devices, and to make a type of magnetoresistance device by controlling the structural parameter of the δ doping.
基金This work was partly supported by theNational Natural Science Foundation of China (Grant No. 19974005).
文摘Fe-O/AlO_x/Fe-O tunnel junctions were prepared by reactive magnetronsputtering under mixed working gas Ar+2 percent O_2. The insulating AlO_x layer of 1-2nm thicknesswas sputtered directly from A1_2O_3 target. Electrode layers were made of 80at. percent iron and20at. percent oxygen. Bottom Fe-O electrode deposited on glass substrate annealed at 473K at thepressure of 3 X 10^(-4) Pa for an hour shows disparate crystalline grain structure, lower electricalresistance and coercivity compared to the as-deposited top electrode. Only crystalline structrureof alpha-Fe is observed in both electrodes. Large tunnel magnetoresistance in large Fe-O/AlO_x/Fe-Ojunctions of 1cm^2 is observed at room temperature and the I-V characteristic curve of the junctionshows that the barrier of the junction is of high quality.
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.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52072102 and 11775224)It was also partially funded through the Open Foundation of the Hefei National Laboratory for Physical Sciences at the Microscale(Grant No.KF2020002).
文摘Because of the wide selectivity of ferromagnetic and ferroelectric(FE)components,electric-field(E-field)control of magnetism via strain mediation can be easily realized through composite multiferroic heterostructures.Here,an MgO-based magnetic tunnel junction(MTJ)is chosen rationally as the ferromagnetic constitution and a high-activity(001)-Pb(Mg_(1/3)Nb_(2/3))_(0.7)Ti_(0.3)O_(3)(PMN-0.3PT)single crystal is selected as the FE component to create a multiferroic MTJ/FE hybrid structure.The shape of tunneling magnetoresistance(TMR)versus in situ E-fields imprints the butterfly loop of the piezo-strain of the FE without magnetic-field bias.The E-field-controlled change in the TMR ratio is up to-0.27%without magnetic-field bias.Moreover,when a typical magnetic field(~±10 Oe)is applied along the minor axis of the MTJ,the butterfly loop is changed significantly by the E-fields relative to that without magnetic-field bias.This suggests that the E-field-controlled junction resistance is spin-dependent and correlated with magnetization switching in the free layer of the MTJ.In addition,based on such a multiferroic heterostructure,a strain-gauge factor up to approximately 40 is achieved,which decreases further with a sign change from positive to negative with increasing magnetic fields.This multiferroic hybrid structure is a promising avenue to control TMR through E-fields in low-power-consumption spintronic and straintronic devices at room temperature.
基金Supported by the National Natural Science Foundation of China under Grant No 11274208
文摘We study the coutrol of gate voltage over the magnetization of a single-molecule magnet (SMM) weakly coupled to a ferromagnetic and a normal metal electrode in the presence of the temperature gradient between two electrodes. It is demonstrated that the SMM's magnetization can change periodically with periodic gate voltage due to the driving oI the temperature gradient. Under an appropriate matching of the electrode polarization, the temperature difference and the pulse width of gate voltage, the SMM's magnetization can be completely reversed in a period of gate voltage. The corresponding flipping time can be controlled by the system parameters. In addition, we also investigate the tunneling anisotropic magnetoresistance (TAMFt) of the device in the steady state when the ferromagnetic electrode is noncollinear with the easy axis of the SMM, and show the jump characteristic of the TAMR.
基金The project supported by Natural Science Foundation of the Education Bureau of Jiangsu Province of China under Grant No.01KJB140007
the“333”Program of Jiangsu Province of China
文摘The tunneling conductance and tunneling magnetoresistance (TMR) are investigated inferromagnet/insulator/ferromagnet/insulator/d-wave superconductor (FM/I/FM/I/d-wave SC) structures by applyingan extended Blonder Tinkham-Klapwijk (BTK) approach. We study the effects of the exchange splitting in the FM,the magnetic impurity scattering in the thin insulator interface of FM/1/FM, and noncollinear magnetizations in adja-cent magnetic layers on the TMR. It is shown (1) that the tunneling conductance and TMR exhibit amplitude-varyingoscillating behavior with exchange splitting, (2) that with the presence of spin-flip scattering in insulator interface of FM/I/FM, the TMR can be dramatically enhanced, and (3) that the TMR depends strongly on the angle between themagnetization of two FMs.
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 the National Key Research and Development Program of China(Grant No.2016YFA0300702)Shanghai Municipal Natural Science Foundation,China(Grant Nos.19ZR1402800,18JC1411400,18ZR1403200,and 17ZR1442600)+1 种基金the Program of Shanghai Academic Research Leader,China(Grant Nos.18XD1400600 and 17XD1400400)the China Postdoctoral Science Foundation(Grant Nos.2016M601488 and 2017T100265)
文摘We reported a study of tunnel magnetoresistance(TMR)effect in single manganite nanowire via the combination of magnetotransport and magnetic force microscopy imaging.TMR value up to 290%has been observed in single(La1-yPry)1-x CaxMnO3 nanowires with varying width.We find that the TMR effect can be explained in the scenario of opening and blockade of conducting channels from inherent magnetic domain evolutions.Our findings provide a new route to fabricate TMR junctions and point towards future improvements in complex oxide-based TMR spintronics.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11834005 and 11674139).
文摘We investigate the spin-related currents and tunnel magnetoresistance through a quantum dot,which is side-coupled with a Majorana fermion zero mode and two thermal-driven ferromagnetic electrodes.It is found that the interplay of Majorana fermion and electrodes'spin polarization can induce a nonlinear thermal-bias spin current.This interplay also decreases the total magnitude of spin or charge current,in either parallel or antiparallel configuration.In addition,a thermal-driven negative tunnel magnetoresistance is found,which is an unique feature to characterize Majorana fermion.With large temperature difference,a step phenomenon is observed in gate tuned spin-up current.When the coupling between quantum dot and topological superconductor is strong enough,this step will evolve into a linear relation,revealing Majorana fermion's robustness.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61571415 and 61622406)the National Key Research and Development Program of China(Grant No.2017YFA0207500)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB30000000)Beijing Academy of Quantum Information Sciences,China(Grant No.Y18G04)
文摘Two-dimensional(2D) magnetic crystals have attracted great attention due to their emerging new physical phenomena. They provide ideal platforms to study the fundamental physics of magnetism in low dimensions. In this research,magnetic tunneling junctions(MTJs) based on XSe2(X = Mn, V) with room-temperature ferromagnetism were studied using first-principles calculations. A large tunneling magnetoresistance(TMR) of 725.07% was obtained in the MTJs based on monolayer MnSe2. Several schemes were proposed to improve the TMR of these devices. Moreover, the results of our non-equilibrium transport calculations showed that the large TMR was maintained in these devices under a finite bias.The transmission spectrum was analyzed according to the orbital components and the electronic structure of the monolayer XSe2(X = Mn, V). The results in this paper demonstrated that the MTJs based on a 2D ferromagnet with room-temperature ferromagnetism exhibited reliable performance. Therefore, such devices show the possibility for potential applications in spintronics.