J. P. Attané

Spin-to-charge conversion using Rashba coupling at the interface between non-magnetic materials

The Rashba effect is an interaction between the spin and the momentum of electrons induced by the spin-orbit coupling (SOC) in surface or interface states. Its potential for conversion between charge and spin currents has been theoretically predicted but never clearly demonstrated for surfaces or interfaces of metals. Here we present experiments evidencing a large spin-charge conversion by the Bi/Ag Rashba interface. We use spin pumping to inject a spin current from a NiFe layer into a Bi/Ag bilayer and we detect the resulting charge current. As the charge signal is much smaller (negligible) with only Bi (only Ag), the spin-to-charge conversion can be unambiguously ascribed to the Rashba coupling at the Bi/Ag interface. This result demonstrates that the Rashba effect at interfaces can be used for efficient charge-spin conversion in spintronics.

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.

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.

Switchable spin-current source controlled by magnetic domain walls.

Using nonlocal spin injection, spin-orbit coupling, or spincaloritronic effects, the manipulation of pure spin currents in nanostructures underlies the development of new spintronic devices. Here, we demonstrate the possibility to create switchable pure spin current sources, controlled by magnetic domain walls. When the domain wall is located at a given point of the magnetic circuit, a pure spin current is injected into a nonmagnetic wire. Using the reciprocal measurement configuration, we demonstrate that the proposed device can also be used as a pure spin current detector. Thanks to its simple geometry, this device can be easily implemented in spintronics applications; in particular, a single current source can be used both to induce the domain wall motion and to generate the spin signal.

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.

Elementary depinning processes of magnetic domain walls under fields and currents

The probability laws associated to domain wall depinning under fields and currents have been studied in NiFe and FePt nanowires. Three basic domain wall depinning processes, associated to different potential landscapes, are found to appear identically in those systems with very different anisotropies. We show that these processes constitute the building blocks of any complex depinning mechanism. A Markovian analysis is proposed, that provides a unified picture of the depinning mechanism and an insight into the pinning potential landscape.