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. 相似文献
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. 相似文献
A generalized approach to study quasiparticle transport across hybrid magnetic tunnel junctions (MTJs) is formulated using the non-equilibrium Green's function technique. This formalism allows for arbitrary thicknesses of the electrodes and the central scattering region comprising of materials with multiple electronic bands, and incorporates the many body interactions present in the electrode regions. While the method can be used to study the transport characteristics of various types of MTJs, we have used it to study the tunneling characteristics and magnetoresistance (MR) of MTJs in which s-f interaction is present at the electrode layers. It is also used to study the transport characteristics of MTJs with hybrid electrodes and double barrier. The magnetic correlation present in the electrodes is found to strongly influence the TMR. Eventhough the magnetic correlation in general suppress the TMR, the TMR is found to be enhanced strongly for certain band occupations of the electrodes. We observe a fall of TMR with increase in the number of layers in the insulating region. Band occupation of the metallic layer present at the middle of the insulating layers in the double barrier MTJ is found to be important in deciding its tunnel characteristics. Origin of the different types of behavior of TMR is analyzed in terms of the spin-dependent tunnel currents. 相似文献
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 magneto 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 the heavily restrained thermal conductance should be responsible for. Thermo-STT in Fe/Vac/Fe MTJs show same order as that in Fe/MgO/Fe MTJs with similar barrier thickness. 相似文献
Using the density functional theory and the nonequilibrium Green's function method, we studied the finite-bias quantum transport in a Cr/graphene/Cr magnetotunnel junction(MTJ) constructed by a single graphene layer sandwiched between two semi-infinite Cr(111) electrodes. We found that the tunneling magnetoresistance(TMR) ratio in this MTJ reached108%, 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 Mg O-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. 相似文献
Temperature- and bias voltage-dependent transport measurements of magnetic tunnel junctions (MTJs) with perpendicularly magnetized Co/Pd electrodes are presented. Magnetization measurements of the Co/Pd multilayers are performed to characterize the electrodes. The effects of the Co layer thickness in the Co/Pd bilayers, the annealing temperature, the Co thickness at the MgO barrier interface, and the number of bilayers on the tunneling magneto resistance (TMR) effect are investigated. TMR-ratios of about 11% at room temperature and 18.5% at 13 K are measured and two well-defined switching fields are observed. The results are compared to measurements of MTJs with Co-Fe-B electrodes and in-plane anisotropy. 相似文献
We report a perpendicular magnetic tunnel junction(p MTJ) cell with a tunnel magnetoresistance(TMR) ratio of nearly 200% at room temperature based on Co Fe B/Ta/Co Fe B as the free layer(FL) and a synthetic antiferromagnetic(SAF) multilayer [Pt/Co]/Ru/[Pt/Co]/Ta/Co Fe B as the reference layer(RL). The field-driven magnetization switching measurements show that the p MTJs exhibit an anomalous TMR hysteresis loop. The spin-polarized layer Co Fe B of SAF-RL has a lower critical switching field than... 相似文献
We present x-ray diffraction experiments and multiple-scattering calculations on the structure and transport properties of a Fe/MgO/Fe(001) magnetic tunnel junction (MTJ). Coherent growth of the top Fe electrode on the MgO spacer is observed only for Fe deposition in ambient oxygen atmosphere leading to a coherent and symmetric MTJ structure characterized by FeO layers at both interfaces. This goes in parallel with calculations indicating large positive tunnel magnetoresistance (TMR) values in such symmetric junctions. The results have important implications for achieving giant TMR values. 相似文献
The recently reported MgAl2O4 tunnel barrier for the magnetic tunnel junctions (MTJs) is considered to be an alternative to the conventional MgO barrier, since a large tunnel magnetoresistance (TMR) ratio was obtained for the MgAl2O4‐based MTJs. In this study, we demonstrated large perpendicular magnetic anisotropy (PMA) arising from the interfaces of Fe(001)/MgAl2O4 layered structures, which can be useful for developing perpendicularly magnetized MgAl2O4‐based MTJs. A PMA energy density of 0.4 MJ/m3 was achieved for an epitaxially grown 0.7 nm thick Fe/MgAl2O4(001). Interestingly, the interface PMA was also obtained for the Fe/non‐epitaxially grown MgAl2O4 structures, which indicates that the crystallographic structure of MgAl2O4 layer has no critical influence on the obtained PMA.
A spintronic theory is developed to study the effect of lattice distortion on the magnetic tunnel junctions(MTJs)consisting of single-crystal barrier and half-metallic electrodes. In the theory, the lattice distortion is described by strain, defect concentration and recovery temperature. All three parameters will modify the periodic scattering potential, and further alter the tunneling magnetoresistance(TMR). The theoretical results show that:(1) the TMR oscillates with all the three parameters;(2) the strain can change the TMR about 30%;(3) the defect concentration will strongly modify the periodic scattering potential, and further change the TMR about 50%;and(4) the recovery temperature has little effect on the periodic scattering potential, and only can change the TMR about 10%. The present work may provide a theoretical foundation to the application of lattice distortion for MTJs consisting of single-crystal barrier and half-metallic electrodes. 相似文献
The microstructures of Co2FeAl and Co2(Cr0.4Fe0.6)Al sputtered films and of their magnetic tunnel junctions (MTJs) have been investigated to discuss the possible reasons for an unexpectedly low tunneling magnetoresistance (TMR). The structure of the Co2FeAl film changed from B2 to L21 with increasing substrate temperature, while that of the Co2(Cr0.4Fe0.6)Al film remained B2 up to 500 °C. The thermodynamically predicted phase separation was not observed in the films. The low TMR values obtained from the MTJs using the Co2FeAl and Co2(Cr0.4Fe0.6)Al films are attributed to the low-spin polarization expected from the low degree of order in these films. The TMR values depend sensitively on the interfacial structure of the tunnel junctions when the degree of order of the film is low. 相似文献
Electron spin-polarized tunneling is observed through an ultrathin layer of the molecular organic semiconductor tris(8-hydroxyquinolinato)aluminum (Alq3). Significant tunnel magnetoresistance (TMR) was measured in a Co/Al2O3/Alq3/NiFe magnetic tunnel junction at room temperature, which increased when cooled to low temperatures. Tunneling characteristics, such as the current-voltage behavior and temperature and bias dependence of the TMR, show the good quality of the organic tunnel barrier. Spin polarization (P) of the tunnel current through the Alq3 layer, directly measured using superconducting Al as the spin detector, shows that minimizing formation of an interfacial dipole layer between the metal electrode and organic barrier significantly improves spin transport. 相似文献
MgO-based magnetic tunnel junctions (MTJs) with a layer sequence Ir22Mn78 or Fe50Mn50 (10 nm)/CoFe (2 nm)/Ru (0.85 nm)/CoFeB (0.5?t<2 nm)/MgO (2.5 nm)/CoFeB (3 nm) have been fabricated. The bias voltage dependence of tunneling magnetoresistance (TMR) is given as a function of the annealing temperature for these MTJs, which shows the TMR ratio changes its sign from inverted to normal at a critical bias voltage (VC) when an unbalanced synthetic antiferromagnetic stack CoFe/Ru/CoFeB is used. VCs change with the thickness of the pinned CoFeB and annealing temperature, which implies one can achieve different VCs by artificial control. The asymmetric VC values suggest that a strong density-of-states modification occurs at bottom oxide/ferromagnet interface. 相似文献
Magnetic tunnel junction (MTJ) structures based on underlayer (CoNbZr)/bufferlayer (CoFe)/antiferromagnet (IrMn)/pinned layer (CoFe)/tunnel barrier (AlOx)/free layer (CoFe)/capping (CoNbZr) have been prepared to investigate thermal degradation of magnetoresistive responses. Some junctions possess a nano-oxide layer (NOL) inside either in the underlayer or bufferlayer. The main purpose of the NOL inclusion was to control interdiffusion path of Mn from the antiferromagnet so that improved thermal stability could be achieved. The MTJs with NOLs were found to have reduced interfacial roughness, resulting in improved tunneling magnetoresistance (TMR) and reduced interlayer coupling field. We also confirmed that the NOL effectively suppressed the Mn interdiffusion toward the tunnel barrier by dragging Mn atoms toward NOL during annealing. 相似文献