Detection of pure spin currents in in-situ fabricated and measured lateral spinvalves
We have developed a novel multi-stage fabrication process for lateral spinvalves that is performed completely in-situ in order to realize clean and well-defined interfaces. In addition, the ferromagnetic layers are topmost and thus accessible to surface sensitive techniques (e.g. SEMPA). The process is based on thermal evaporation and structuring with UHV-FIB. Our spinvalves comprise two ferromagnetic Co wires of different length that are attached to Cu leads.
Figure: SEM micrograph of an in-situ fabricated lateral spin valve. FM1 and FM2 are ferromagnetic Co wires (blue) attached to Cu leads C1 to C4 (red).
For the non-local transport measurements a current I is applied between C1 and C4 in order to create spin accumulation in the Cu lead between C1 and C2. The pure spin current signal is detected as a voltage VS across C2 and C3, which depends on the relative magnetic alignment of FM1 and FM2.
Figure: Pure spin current signal RS=VS/I measured for two different excitation currents. The two levels in each measurement correspond to the parallel and antiparallel alignment of the magnetizations in FM1 and FM2. The magnitude of the effect of about 1 mΩ indicates clean interfaces.
The non-reproducible switching (e.g. at negative magnetic field) is due the formation of magnetic domains in the Co wires, which are stabilized by ion-beam induced roughness of the substrate. The SEMPA measurements indicate the formation of the so-called concertina domain structure.
Figure: SEM topography and corresponding SEMPA image of the ferromagnetic wires. In spite of their dimension (10 nm thick, 220 to 280 nm wide, and about 4 µm long) they reveals a rich domain structure similar to the schematically shown concertina structure.
J. Mennig, F. Matthes, D. E. Bürgler, and C. M. Schneider
Observation and implications of magnetic domains in lateral spin valves
J. Appl. Phys. 111, 07C504 (2012).