Switching properties of a tunneling junction connected to a spin valve
TL;DR: In this paper, the authors investigated the switching properties of a spin valve and tunneling junction with a spin-polarized fully relativistic approach and showed that the existence of a stable and a metastable state, a necessary condition for a switching device, is essentially determined by the free energy contributions of the interfaces of that magnetic slab that is part of the spin valve as well as of the tunnel.
Abstract: The switching properties of a prototype system containing a spin valve as well as a tunneling junction are investigated by means of a spin-polarized fully relativistic approach. Shown are the changes in the free energy and in the magnetoresistance when the orientation of the magnetization in the magnetic slabs of such a system is changed individually. It is demonstrated that the existence of a stable and a metastable state, a necessary condition for a switching device, is essentially determined by the free energy contributions of the interfaces of that magnetic slab that is part of the spin valve as well as of the tunneling junction. Furthermore, in estimating individual switching times, it is found that most of the gain in magnetoresistance occurs within a time range of about 20 ps, the time to achieve complete switching, however, being about 1.5 ns, which is close to what is found in recent experimental results.
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Journal Article•
TL;DR: In this paper, the relationship between spin transfer and tunnel magnetoresistance (TMR) under finite bias was investigated, and it was shown that the spin torque per unit current exerted on the free layer decreases by < 10% over a bias range where the TMR decreases by > 40%.
Abstract: We employ the spin-torque response of magnetic tunnel junctions with ultrathin MgO tunnel barrier layers to investigate the relationship between spin transfer and tunnel magnetoresistance (TMR) under finite bias, and find that the spin torque per unit current exerted on the free layer decreases by < 10% over a bias range where the TMR decreases by > 40%. This is inconsistent with free-electron-like spin-polarized tunneling and reduced-surface-magnetism models of the TMR bias dependence, but is consistent with magnetic-state-dependent decay lengths in the tunnel barrier.
3 citations
TL;DR: In this paper, an experimental study of the electric properties of Pt/Permalloy bilayers based on a simultaneous application of an in-plane microfrequency current and an external magnetic field is simulated on a fully relativistic ab initio level by considering the resistivity as an implicit function of the free energy.
Abstract: A recent experimental study of the electric properties of Pt/Permalloy bilayers based on a simultaneous application of an in-plane microfrequency current and an external magnetic field is simulated on a fully relativistic ab initio level by considering the resistivity as an implicit function of the free energy. It is found that the oscillations detected experimentally are caused by the different behavior of out-of-plane and in-plane resistivities in the vicinity of that value of the free energy that corresponds to the resonant field induced by the applied current. A necessary precondition for such oscillations is a sizeable perpendicular anisotropy, which is not the case in systems consisting only of Permalloy. It is shown that the observed phenomenon is essentially an interface effect.
TL;DR: In this article, the time evolution of the density corresponding to the polarization operator, originally constructed to commute with the Dirac Hamiltonian in the absence of an external electromagnetic field, was investigated in terms of the time-dependent Dirac equation taking the presence of external electromagnetic fields into account.
Abstract: The time evolution of the density corresponding to the polarization operator, originally constructed to commute with the Dirac Hamiltonian in the absence of an external electromagnetic field, is investigated in terms of the time-dependent Dirac equation taking the presence of an external electromagnetic field into account. It is found that this time evolution leads to ‘tensorial’ and ‘vectorial’ particle current densities and to the interaction of the spin density with the external electromagnetic field. As the time evolution of the spin density does not refer to a constant of motion (continuity condition) it only serves as auxiliary density. By taking the non-relativistic limit, it is shown that the polarization, spin and magnetization densities are independent of electric field effects and, in addition, no preferred directions can be defined.
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IBM1
TL;DR: In this paper, a new mechanism was proposed for exciting the magnetic state of a ferromagnet, where a transfer of vectorial spin accompanied an electric current flowing perpendicular to two parallel magnetic films connected by a normal metallic spacer.
5,824 citations
TL;DR: In this article, the spin angular momentum from a spin-polarized current to a ferromagnet can generate sufficient torque to reorient the magnet's moment, which could enable the development of efficient electrically actuated magnetic memories and nanoscale microwave oscillators.
Abstract: The transfer of spin angular momentum from a spin-polarized current to a ferromagnet can generate sufficient torque to reorient the magnet’s moment. This torque could enable the development of efficient electrically actuated magnetic memories and nanoscale microwave oscillators. Yet difficulties in making quantitative measurements of the spin-torque vector have hampered understanding. Here we present direct measurements of both the magnitude and direction of the spin torque in magnetic tunnel junctions, the type of device of primary interest for applications. At low bias V, the differential torque dτ/dV lies in the plane defined by the electrode magnetizations, and its magnitude is in excellent agreement with recent predictions for near-perfect spin-polarized tunnelling. We find that the strength of the in-plane differential torque remains almost constant with increasing bias, despite a substantial decrease in the device magnetoresistance, and that with bias the torque vector also rotates out of the plane.
600 citations
TL;DR: In this article, a generalized stochastic Landau-Lifshitz equation and its corresponding Fokker-Planck equation were proposed for the magnetization dynamics in the presence of spin-transfer torques.
Abstract: We propose a generalized stochastic Landau-Lifshitz equation and its corresponding Fokker-Planck equation for the magnetization dynamics in the presence of spin-transfer torques. Since the spin-transfer torque can pump a magnetic energy into the magnetic system, the equilibrium temperature of the magnetic system is ill defined. We introduce an effective temperature based on a stationary solution of the Fokker-Planck equation. In the limit of high-energy barriers, the law of thermal agitation is derived. We find that the N\'eel-Brown relaxation formula remains valid as long as we replace the temperature by an effective one that is linearly dependent on the spin torque. We carry out the numerical integration of the stochastic Landau-Lifshitz equation to support our theory. Our results agree with existing experimental data.
378 citations
TL;DR: In this article, the effect of electrode composition on the tunnel magnetoresistance (TMR) ratio of (CoxFe100−x)80B20∕MgO∕(Cox Fe100−X)80b20 pseudo-spin-valve magnetic tunnel junctions (MTJs) was investigated.
Abstract: The authors investigate the effect of electrode composition on the tunnel magnetoresistance (TMR) ratio of (CoxFe100−x)80B20∕MgO∕(CoxFe100−x)80B20 pseudo-spin-valve magnetic tunnel junctions (MTJs). TMR ratio is found to strongly depend on the composition and thicknesses of CoFeB. High resolution transmission electron microscopy shows that the crystallization process of CoFeB during annealing depends on the composition and the thicknesses of the CoFeB film, resulting in different TMR ratios. A TMR ratio of 500% at room temperature and of 1010% at 5K are observed in a MTJ having 4.3nm and 4-nm-thick (Co25Fe75)80B20 electrodes with a 2.1-nm-thick MgO barrier annealed at 475°C.
308 citations