We report an unconventional oscillatory tunnel magnetoresistance as a function of the applied bias in double barrier magnetic tunnel junctions that were made of two Al 2 O 3 barriers sandwiched by three ferromagnetic layers. When the center ferromagnetic layer is aligned antiparallel to the top and bottom magnetic layers, a distinct magnetoresistance oscillation appears with respect to the increase of the bias voltage at 4.2 K and at room temperature. The period of the oscillation is about 1.6 mV.
We report the observation and micromagnetic analysis of current-driven
magnetization switching in nanoscale ring-shaped magnetic tunnel junctions.
When the electric current density exceeds a critical value of the order of
$6\times 10^{6}$A/cm$^2$, the magnetization of the two magnetic rings can be
switched back and forth between parallel and antiparallel onion states.
Theoretical analysis and micromagnetic simulation show that the dominant
mechanism for the observed current-driven switching is the spin torque rather
than the current-induced circular Oersted field
Perpendicular magnetic tunnel junctions (pMTJs) with tunneling magnetoresistance (TMR) as high as 14.7% at room temperature were fabricated. The continuous film and pMTJs with Co/Pt multilayer magnetic electrodes and AlOx tunnel barrier were annealed at different temperatures and the effect of annealing on their properties was investigated. The hysteresis loops and X-ray reflectivity measurement show that the interdiffusion of Co and Pt atoms is slight when annealed below 523 K. However, the patterned magnetic tunnel junction gets TMR ratio from 12.3% to the maximum value of 14.7% after annealing at 483 K for 1 h.
Because spin-flip length is longer than the electron mean-free path in a metal, past studies of spin-flip scattering are limited to the diffusive regime. We propose to use a magnetic double barrier tunnel junction to study spin-flip scattering in the nanometer sized spacer layer near the ballistic limit. We extract the voltage and temperature dependence of the spin-flip conductance G s in the spacer layer from magnetoresistance measurements. In addition to spin scattering information including the mean-free path (70 nm) and the spin-flip length (1:0-2:6 m) at 4.2 K, this technique also yields information on the density of states and quantum well resonance in the spacer layer. DOI: 10.1103/PhysRevLett.97.106605 PACS numbers: 72.25.Rb, 72.25.Ba, 73.63.ÿb, 85.75.ÿd One of the challenges in the physics of spin-based electronics, or spintronics [1,2], is the study of spin-flip scattering and its effect on magnetotransport, in particular, on spin injection and accumulation [3][4][5][6][7][8][9]. Spin-flip scattering in nonmagnetic metals has been studied by connecting a metal wire to multiple magnetic electrodes [9,10]. Because of the very long spin-flip length (hundreds of nanometers), reliable determination of the strength of spin-flip scattering requires the use of metal wires many times the length of the mean-free-path. These measurements therefore are in the diffusive regime.In magnetic multilayers and tunnel junctions the size of the constituent layers rarely reaches the diffusive regime. Most of these layers are nanometers in thickness and electron transport in these layers are nearly ballistic. So far there has not been an experimental approach that allows the study of spin-flip scattering near the ballistic limit. A further motivation for studying spin-flip scattering in nanometer sized films is the effect of a large bias. While the voltage effect over a long metal wire is almost certainly linear, there can be large nonlinear effects of the same voltage over a one-nanometer thin film.In this Letter we present a novel experimental approach to the study of spin-flip scattering in ultrathin metal films in the ballistic regime. The key to this new approach is to reduce the channel conductance for each spin to the same order as the spin-flip conductance G s between the two spin channels, without reducing the electron mean-free-path or increasing the sample size. Tunnel barriers are the obvious choice to serve this purpose. By sandwiching a thin Cu film between two tunnel barriers, the voltage and temperature dependence of the spin-flip conductance G s between the two spin channels in the Cu layer can be extracted from the tunneling magnetoresistance (TMR) measurements. We find that the spin-flip scattering increases linearly with the temperature and at a rate proportional to the Cu layer thickness. This argues for a phononic origin of spin-flip scattering. The bias voltage dependence is highly nonlinear and reflects the electron density of states in the Cu layer near the Fermi energy. By correlating the spin-f...
Tunneling giant magnetoresistance (MR) of the Fe–Al2O3 nanogranular films has been observed over a wide range of Fe volume fraction x and it took a maximum of 4.4% at room temperature for the film with x=0.45 at H=10 kOe. Furthermore, the field dependence of MR of the samples is well described by the form proportional to the square of the magnetization. Moreover, an estimate of the magnetic anisotropy energy density Ku increases with the decrease of x, yielding a value 2 orders of magnitude greater than the value for bulk Fe when x=0.23. The Bloch’s law, MS(T)=MS0(1−BTb), can also hold for all the samples but with nonbulk parameters dependent on the Fe volume fraction. These results reveal a percolation effect on the magnetic properties, as well as the conductance, in such nanogranular films.
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