Thermal spin-transfer in Fe-MgO-Fe tunnel junctions

We compute thermal spin transfer torques (TST) in Fe-MgO-Fe tunnel junctions using a first principles wave function-matching method. At room temperature, the TST in a junction with 3 MgO monolayers amounts to 10^-7J/m^2/K, which is estimated to cause magnetization reversal for temperature differences over the barrier of the order of 10 K. The large TST can be explained by multiple scattering between interface states through ultrathin barriers. The angular dependence of the TST can be very skewed, possibly leading to thermally induced high-frequency generation.Comment: 5 pages, 5 figure

Tunneling magnetoresistance in Mn2_2Au-based pure antiferromagnetic tunnel junction

Antiferromagnetic (AF) spintronics is merit on ultra-high operator speed and stability in the presence of magnetic field. To fully use the merit, the device should be pure rather than hybrid with ferromagnet or ferrimagnet. For the magnetism in the antiferromagnet is canceled by that of different sublattices, breaking the symmetry in the material can revive the native magnetism, which can be detected by the magnetoresistance (MR) effect. Achieving noticeable MR effect in the pure AF device is diffcult but essential for the AF spintronic applications. Here, we study the tunnel magnetoresistance(TMR) effect in the Nb/Mn$_2$Au/CdO/Mn$_2$Au/Nb pure AF magnetic tunnel junctions (AF-MTJs) based on a first-principle scattering theory. Giant TMRs with order of 1000% are predicted in some symmetric junctions, which is originated from the interfacial resonance tunneling effect related with the k dependent complex band structures of CdO and Mn$_2$Au in companion with the enhanced spin polarization of the interfacial magnetic atoms. The effect of voltage bias and interfacial disorder such as Oxygen vacancy, Manganese vacancy, and Manganese-Cadmium exchanges at Mn2Au/CdO interfaces are studied also. Our studies suggest Nb/Mn$_2$Au/CdO/Mn$_2$Au/Nb AFMTJs promising material for AF spintronic application, and rocksalt CdO a potential symmetry filtering material for spintronic applications

Angular momentum transfer torques in spin valves with perpendicular magnetization

Spin valves incorporating perpendicularly magnetized materials are promising structures for memory elements and high-frequency generators. We report the angular dependence of the spin-transfer torque in spin valves with perpendicular equilibrium magnetization computed by first-principles circuit theory and compare results with experiments by W.H. Rippard c.s. [Phys. Rev. B 81, 014426 (2010)] on the CoFe|Cu|CoNi system. Furthermore, we predict a non-monotonous ("wavy") spin-transfer torque when the Cu spacer is replaced by a Ru layer.Comment: 6 pages, 4 figure

Spin transfer torque on magnetic insulators

Recent experimental and theoretical studies focus on spin-mediated heat currents at interfaces between normal metals and magnetic insulators. We resolve conflicting estimates for the order of magnitude of the spin transfer torque by first-principles calculations. The spin mixing conductance G^\uparrow\downarrow of the interface between silver and the insulating ferrimagnet Yttrium Iron Garnet (YIG) is dominated by its real part and of the order of 10^14 \Omega^-1m^-2, i.e. close to the value for intermetallic interface, which can be explained by a local spin model.Comment: 4 pages, 4 figures, 2 table

Magnetism in Cr-doped ZnS: Density-functional theory studies

We investigated the magnetism and aggregation trends in cubic Zn1-xCrxS using the density-functional theory calculations.We demonstrate that all studied configurations show ground state half-metallic ferromagnetism (HMF); and Cr impurities are energetically favorable to planar cluster into delta-doping structures. The single-layer delta-doping structures of Zn0.75Cr0.25S and Zn0.875Cr0.125S show ferromagnetic stabilization energies (\Delta E_AF) of 0.551 and 0.561 eV/Cr-Cr pair, respectively. The half-layer delta-doping structure of Zn0.875Cr0.125S and double-layer delta-doping structure of Zn0.75Cr0.25S show \Delta E_AF of 0.394 and 0.166 eV/Cr-Cr pair, respectively. Furthermore, our studies indicate that the cubic ZnS/CrS heterostructure, one extreme situation of the delta-doping structure, also shows ground state HMF. The origin of HMF is discussed using a simple crystal field model. Finally, we anticipate the potential spintronics application of Zn1-xCrxS.Comment: 13 pages, 4 figure

Structure and Magnetism in Mn Doped Zirconia: Density-functional Theory Studies

Using the first-principles density-functional theory plan-wave pseudopotential method, we investigate the structure and magnetism in 25% Mn substitutive and interstitial doped monoclinic, tetragonal and cubic ZrO2 systematically. Our studies show that the introduction of Mn impurities into ZrO2 not only stabilizes the high temperature phase, but also endows ZrO2 with magnetism. Based on the simple crystal field theory (CFT), we discuss the origination of magnetism in Mn doped ZrO2. Moreover, we discuss the effect of electron donor on magnetic semiconductors, and the possibility as electronic structure modulator.Comment: 10 pages, 3 figures, 26 reference