Spin polarization P is a key characteristic of any metallic ferromagnet to be incorporated into a spintronic device. It is defined as
The method of real-time Andreev reflection where a superconducting tip is used to probe the ballistic or tunnel current passing between the ferromagnet and the tip as the tip approaches the surface is being developed to investigate rare earth metals and new magnetic materials produced in the group.
Spin electonics depends on transport of spin-polarized electrons, or transfer of spin angular momentum in a conducting medium. The prospect of spin transport in organics is enticing, as it could add a new dimension to organic electronics. Studies of thin-film stacks with thin organic layers show quite sizable magnetoresistance effects at room temperature, which can be attributed to single or multistep tunelling across the organic layer. However, lateral spin transport which depends on diffusion of spin-polarized electrons through the organic layer is problematic. Many structures with organic semiconductor crystals or thin films exhibit no magnetoresistance. Either the spin polarization is destroyed on injection, or the carriers are spin-paired bipolarons.
Spin currents can be driven by unpolarized charge currents in a different direction. This is the spin Hall effect, due to spin-orbit scattering in a metal. The spin current can be used to switch a spin valve by spin-transfer torque.
Magnetic tunnel junctions can be used as sensors when the free and pinned layers have orthogonal easy directions of magnetization in zero field. These sensors are being integrated into a microfluidic channel to detect the passage of magnetic nanowire barcodes which may be functionalized and tagged with biomolecules.
Contact Plamen Stamenov
Point contact Andreev reflection from Erbium: The role of external magnetic field and the sign of the spin polarization, P. Stamenov, J. Appl Phys 111 07C519 (2012)
Electron and spin transport studies of gated lateral organic devices, S. Alborghetti, J. M. D. Coey and P. Stamenov, J. Appl. Phys 112 124510 (2012); doi: 10.1063/1.4770230
Yoke-shaped MgO barrier magnetic tunnel junction sensors, J. Y. Chen. N Carroll, J F Feng and J. M. D. Coey, Appl. Phys. Letters 101 262402 (2012); doi 10.1063/1.477318