C. Beigné

Experimental evidences of a large extrinsic spin Hall effect in AuW alloy

We report an experimental study of a gold-tungsten alloy (7 at. % W concentration in Au host) displaying remarkable properties for spintronics applications using both magneto-transport in lateral spin valve devices and spin-pumping with inverse spin Hall effect experiments. A very large spin Hall angle of about 10% is consistently found using both techniques with the reliable spin diffusion length of 2 nm estimated by the spin sink experiments in the lateral spin valves. With its chemical stability, high resistivity, and small induced damping, this AuW alloy may find applications in the nearest future.

Domain wall pinning on strain relaxation defects in FePt(001)/Pt thin films

Thin FePt (001) films, grown by molecular-beam epitaxy on Pt(001), exhibit a very large perpendicular magnetic anisotropy (Ku=5×106 J m−3) and a 100% magnetic remanence in perpendicular field. The lattice misfit between FePt and Pt (1.5%) relaxes through the pileup of a/6 〈112〉 partial dislocations along {111} planes, leading to the formation of microtwins. Atomic force microscopy images demonstrate that this process induces a spontaneous rectangular nanostructuration of the sample, while magnetic force microscopy shows that the microtwins act as pinning sites for the magnetic walls. This leads to square magnetic domains and explains the large coercivity associated with the domain wall propagation.

Magnetization reversal dominated by domain wall pinning in FePt based spin valves

In this paper, we study FePt/NM/FePt//MgO (NM=Pt or Pd) spin valves with perpendicular magnetization deposited by molecular beam epitaxy. Using extraordinary Hall effect and magnetoresistance, we show that the electrodes can be of different coercivities and magnetically decoupled, with current-in-plane magnetoresistances up to 0.8% at room temperature. Finally, using magnetic force microscopy observations, we prove that the different coercivities of the electrodes are controlled by different magnetization reversals and domain-wall pinning, thus allowing the obtaining of an antiparallel state.

Spin transport in p-type germanium

We report on the spin transport properties in p-doped germanium (Ge-p) using low temperature magnetoresistance measurements, electrical spin injection from a ferromagnetic metal and the spin pumping-inverse spin Hall effect method. Electrical spin injection is carried out using three-terminal measurements and the Hanle effect. In the 2-20 K temperature range, weak antilocalization and the Hanle effect provide the same spin lifetime in the germanium valence band (≈1 ps) in agreement with predicted values and previous optical measurements. These results, combined with dynamical spin injection by spin pumping and the inverse spin Hall effect, demonstrate successful spin accumulation in Ge. We also estimate the spin Hall angle θ(SHE) in Ge-p (6-7 x 10(-4) at room temperature, pointing out the essential role of ionized impurities in spin dependent scattering.

Magnon magnetoresistance of NiFe nanowires: Size dependence and domain wall detection

The magnetoresistance of permalloy (Ni84Fe16) nanowires of various widths (down to 50 nm) has been measured for fields applied along the wires. The enhancement of the shape anisotropy in the narrowest widths leads to the disappearance of the anisotropic magnetoresistance signal, the remaining contribution to the magnetoresistance being that of the magnons. Using constrictions to pin a domain wall, we show that the magnon magnetoresistance signal can give access to the position of the domain wall along the wire.

Millimeter-scale layered MoSe2 grown on sapphire and evidence for negative magnetoresistance

Molecular beam epitaxy technique has been used to deposit a single layer and a bilayer of MoSe2 on sapphire. Extensive characterizations including in-situ and ex-situ measurements show that the layered MoSe2 grows in a scalable manner on the substrate and reveals characteristics of a stoichiometric 2H-phase. The layered MoSe2 exhibits polycrystalline features with domains separated by defects and boundaries. Temperature and magnetic field dependent resistivity measurements unveil a carrier hopping character described within two-dimensional variable range hopping mechanism. Moreover, a negative magnetoresistance was observed, stressing a fascinating feature of the charge transport under the application of a magnetic field in the layered MoSe2 system. This negative magnetoresistance observed at millimeter-scale is similar to that observed recently at room temperature in WS2 flakes at a micrometer scale [Zhang et al., Appl. Phys. Lett. 108, 153114 (2016)]. This scalability highlights the fact that the underl...

Tailoring magnetism in CoNi films with perpendicular anisotropy by ion irradiation

This paper reports on the influence of ion irradiation on the magnetic properties of Co∕Ni multilayers with perpendicular magnetic anisotropy (PMA). This material is a very promising candidate for ultrahigh density spintronic applications since it exhibits high polarization and low damping parameters. We show that PMA can be tailored in a controlled way by using uniform He+ ion irradiation or focused Ga+ ion beam.

In-plane and out-of-plane spin precession in lateral spin-valves

The spin signal variations of Al/NiFe lateral spin-valves with AlOx interfaces are studied under different applied field orientations. For applied fields perpendicular to the sample plane, the spin signal is governed by the spin precession and by the angular dephasing of spins in the channel, i.e., the Hanle effect. We show that using narrow permalloy wires with large shape anisotropies, it is also possible to observe spin precession with in-plane magnetic fields. In this case, the precessing spin current possesses an out-of plane component, which means that by tuning properly the external field it is possible to control along the three dimensions the orientation of the spins arriving on the ferromagnetic detector. Finally, fits of our data allow for both in and out-of plane fields extracting the relevant characteristics of our lateral spin-valves.

Dimensionality effects on the magnetization reversal in narrow FePt nanowires

The magnetization reversal of 10 nm thick FePt nanowires has been studied for widths down to 30 nm. Above 500 nm, the magnetic domains grow within a dendritic structure. Below 300 nm, the reversal takes place by propagation of a single domain wall (DW), and the coercivity increases. Below 50 nm, the coercivity increase is such that a mix of nucleation and DW propagation appears. These results suggest that the reversal process is determined by the comparison of the wire dimensions with four characteristic lengths: the dendrite width, the disorder length, the mean edge roughness, and the nucleation distance.

Comparison of the use of NiFe and CoFe as electrodes for metallic lateral spin valves

Spin injection and detection in Co60Fe40-based all-metallic lateral spin valves have been studied at both room and low temperatures. The obtained spin signals amplitudes have been compared to those of identical Ni80Fe20-based devices. The replacement of Ni80Fe20 by CoFe allows increasing the spin signal amplitude by up to one order of magnitude, thus reaching 50 mΩ at room temperature. The spin signal dependence with the distance between the ferromagnetic electrodes has been analyzed using both a 1D spin-transport model and finite element method simulations. The enhancement of the spin signal amplitude when using CoFe electrodes can be explained by a higher effective polarization.