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As the first magnetic random access memories are finding their way onto the market, an important issue remains to be solved: the current density required to write magnetic bits becomes prohibitively high as bit dimensions are reduced. Recently, spin–orbit torques and the spin-Hall effect in particular have attracted significant interest, as they enable magnetization reversal without high current densities running through the tunnel barrier. For perpendicularly magnetized layers, however, the technological implementation of the spin-Hall effect is hampered by the necessity of an in-plane magnetic field for deterministic switching. Here we interface a thin ferromagnetic layer with an anti-ferromagnetic material. An in-plane exchange bias is created and shown to enable field-free S HE-driven magnetization reversal of a perpendicularly magnetized Pt/Co/IrMn structure. Aside from the potential technological implications, our experiment provides additional insight into the local spin structure at the ferromagnetic/anti-ferromagnetic interface

We report multi-channel electron transport in nano-contacts fabricated using focused electron beam induced deposited (FEBID) cobalt and focused ion beam induced deposited (FIBID) tungsten. Anomalous Andreev reflection (AR) effect is observed to which the conventional Blonder–Tinkham–Klapwijk (BTK) fit cannot be applied. In specific, we have observed multiple number of shoulders near the AR peak, whose origin is unknown in literature. We explain this effect based on a simple model that takes into account the material properties of the FIBID grown W superconductor, as well as the specific interface properties that are an outcome of using FEBID/FIBID as a fabrication technique. We show that numerical calculations using the BTK approximation based on the consideration of multiple channels generate similar shoulders as we observed in the AR experiments. Electrical measurements and x-ray photoemission spectroscopy carried out on FIBID W deposits puts additional evidence towards multi-channel current transport occuring at the interface of the nanocontacts.

The Gilbert damping in perpendicularly magnetized Pt/Co/AlOx films is studied by means of the time-resolved magneto-optical Kerr effect. The Gilbert damping constant is observed to depend strongly on the AlOx layer thickness and the applied magnetic field. The magnetic field dependence is explained by extrinsic contributions to the damping due to inhomogeinities in the thin films. The intrinsic Gilbert damping is found to vary between 0.11 and 0.28 as a function of the AlOx thickness, which can be attributed to spin pumping from Co into the adjacent Pt film.

Co2MnSi films were recently reported to show a significant increase in current-perpendicular-to-plane-giant-magnetoresistance upon annealing. Here, nuclear magnetic resonance was used to study the impact of annealing on the structure of such films. Below 550¿°C, no long-range L2 1 -order is observed, while annealing above 550¿°C leads to the formation of the ideal L2 1 configuration, however, with a distinct degree of off-stoichiometry. Further evidence from restoring field measurements hints that interdiffusion may account for the drop in magnetoresistance observed for samples annealed above 600¿°C. These results show that optimizing films for spintronics involves the identification of the best annealing temperature, high enough for long-range order to emerge, but low enough to maintain smooth interfaces.

In this work, the spin-echo nuclear magnetic resonance (NMR) technique is used to probe the local structure of Co2FeAl0.5Si0.5 bulk samples. The 59Co NMR spectrum of the Heusler compound Co2FeAl0.5Si0.5 consists of four main resonance lines with an underlying sub-structure. The splitting into the main resonance lines is explained by contributions of the B2 type structure. The sub-lines are attributed to a random distribution of Al and Si. By comparing the experimental results with an appropriate multinomial distribution, the fraction of the Al/Si intermixing and the ratio between the contributing structure types is assigned. The main structural contribution of as-cast bulk samples is of B2 type with 38% of L21 contributions. The L21 contribution can be enhanced to 59% by an appropriate annealing process. However, B2 contributions are still present after annealing. Additional foreign phases such as fcc-Co and Co-Al, with relative contributions of less than one percent, are also found in both as-cast and annealed samples. Resonance lines related to slight amounts of the ternary, parental Heusler compounds Co2FeAl and Co2FeSi are also observed.

We report experimentally obtained magnetic domain wall (DW) velocities of current-assisted field-driven DW creep in perpendicularly magnetized Pt/Co/Pt. We have intentionally introduced an asymmetry in the stacks by using different thicknesses of the two Pt layers sandwiching the Co layer. Thereby, it is tested whether conflicting current-induced domain wall motion (CI-DWM) results may be intrinsically related to the basic layout and growth. We sketch a scenario which could be at the basis of contradicting reports in literature where the direction of CI-DWM conflicts with spin-torque-transfer theory, allowing the sign of the current-induced effect on DW motion to be tuned.

We report the temperature dependence of the resistivity, the anisotropic magnetoresistance and the Hall effect of iron microwires grown by focused-electron-beam-induced deposition. By modifying the growth conditions in a controllable way, we study wires with iron compositions varying from 45% to 70%, which present different electrical conduction mechanisms, with resistivity values differing over three orders of magnitude. The magnetoresistance depends highly on the composition, and it can be understood by a subtle interplay between the anisotropic magnetoresistance and intergrain magnetoresistance due to their complex microstructure, consisting of an iron–carbon–oxygen amorphous matrix. A giant value for the anomalous Hall effect is found, which we explain by a large contribution of the skew scattering mechanism. The present results emphasize the correlation between the exotic microstructure of the microwires, and their magnetotransport properties.

In experiments on current-driven domain wall (DW) motion in nanostrips with perpendicular magnetic anisotropy (PMA), the initial DW preparation is usually not well controlled. We demonstrate precise control of DW injection using Ga and novel He focused ion beam (FIB) irradiation to locally reduce the anisotropy in part of a Pt/Co/Pt strip. DWs experience pinning at the boundary of the irradiated area. This DW pinning is more pronounced at the He irradiation boundary compared to Ga. This is attributed to a better He beam resolution, causing an anisotropy gradient over a much smaller length scale and hence, a steeper energy barrier for the DW. The results indicate that He FIB is a useful tool for anisotropy engineering of magnetic devices in the nanometer range.

We report on the change in the structural and magnetic properties of magnetically soft ternary Co80-xFexB20 alloys as a function of composition, thickness, and annealing temperature. Compositions high in cobalt show a significant change in coercivity after annealing. This is explained using the random anisotropy model by relating the magnetic exchange length to the grain size of the crystallites. The presented results are a systematic study explaining trends seen in the transition from soft to hard magnetic behavior, providing insight into why the soft CoFeB alloys have been so successful recently in spintronic devices

We systematically study the changes in the local atomic environments of Co in CoFe-Al alloys as a function of Al content by means of nuclear magnetic resonance. We find that a Co2 FeAl Heusler type structure is formed on a local scale. The observed formation of a highly spin-polarized Heusler compound may explain the improved magnetotransport properties in CoFe-Al based current-perpendicular-to-the-plane spin-valves.

We propose a magnetic domain wall (DW) oscillator scheme, in which a low dc current excites gigahertz angular precession of a DW at a fixed position. The scheme consists of a DW pinned at a magnetic anisotropy step in a perpendicularly magnetized nanostrip. The frequency is tuned by the current flowing through the strip. A perpendicular external field tunes the critical current density needed for precession, providing great experimental flexibility. We investigate this system using a simple one-dimensional model and full micromagnetic calculations. This oscillating nanomagnet is relatively easy to fabricate and could find application in future nanoscale microwave sources. © 2011 American Institute of Physics.

For applications of domain wall (DW) motion in magnetic devices, it is vital to control the creation and position of the DW. We use Ga+ irradiation of Pt/Co/Pt strips to locally change the perpendicular magnetic anisotropy. This allows us to controllably inject DWs into a device at a tunable field. The observed initial linear decrease and subsequent increase in the DW injection field upon increasing irradiation dose are explained by micromagnetic simulations and an analytical one-dimensional model.