Electronics, Photonics, Spintronics, Plasmonics And Now Scientists Introduce A New Field: Spinplasmonics
6 Jun, 2007 03:15 pm
Researchers at the Ultrafast Optics and Nanophotonics Laboratory at the University of Alberta (U of A), Edmonton, Canada and the Naval Research Laboratory (NRL), Washington, DC. have opened a door to a new field that could potentially pave the way for the development of novel multifunctional light-controlled devices.
With the growing demand for high-speed, high bandwidth information technology and the realization of the bottleneck inherent to the semiconductor device technology
(for a nanosize semiconductor device, the laws of quantum mechanics take control over its performance rendering the devices inoperable), there has been increasing research and interest in the use of photonic devices as alternatives. A new branch of photonics that uses plasmons (coherent surface electron oscillation within the metallic nanostructures) is known as Plasmonics. Plasmonics offers a way to channel light on a chip using subwavelength metallic structures and focus the electromagnetic energy into nanovolumes. There have been several proposals for nanoscale light radiation-driven circuits that convert light into surface plasmons, which would then propagate and be processed by logic elements prior to conversion back into light. Interestingly, this metallic-based circuitry could be also be used to carry direct electrical signals. Moreover, rather than exploiting the electron charge, as in the case of semiconductor devices, one way to achieve even higher functionalities is via the manipulation of the electron's quantum state as it interacts with a magnetic field, known as the electron spin state. The Spintronic field exploits electron spin rather than charge, thus offering nano-scale logic devices with enhanced functionality and lower power consumption. While Plasmonics takes advantage of the electron charge, and Spintronics utilizes the electron spin, Spinplasmonics does both. By harnessing the electron's spin state and utilizing spin-polarized electrical currents, several metal-based devices have already been demonstrated.
The U of A and the NRL team have applied plasmonics principles to spintronics technology and created a novel way to control the quantum state of an electron's spin, thus combining the advantages of both spintronic and plasmonic technologies. In a simple manifestation of the new class of spinplasmonic devices, electromagnetic radiation is coupled to the metallic ferromagnetic/nonmagnetic spintronic structure consisting of ferromagnetic (for example, Cobalt, Nickel, or Iron) and nonmagnetic (for example Gold, Silver, Copper, or Aluminium) metals. An externally applied magnetic field orients the magnetic domains in a ferromagnetic layer, and therefore lines up the electron spins in a specific direction along the magnetic field. As the radiation penetrates a few nanometers within the surface and reaches the interfaces of the ferromagnetic/nonmagnetic spintronic structure, electrons in the metals are then set in motion by the radiation electric field and thus creates plasmonic currents having specific direction of the electron's spins (that is, spin polarized plasmonic currents). The plasmon current injection occurs from the ferromagnetic into the nonmagnetic metals, and as they get piled up in the nonmagnetic metals, the nonmagnetic metals become weakly magnetized and a large resistance develops at the interface between the ferromagnetic and the nonmagnetic metals to stop further flow of spin-polarized electrons. Effectively, the spin-polarized electrons in the nonmagnetic layer create resistive loss for the plasmons. This situation is similar to electrically driven spin injected current in traditional spintronic devices. The U of A and NRL team were able to demonstrate a plasmonically- active spintronic media and have shown light switching by controlling the orientation of electron spins.
"To us this is almost a natural evolution of the two fields. The idea is simple but the hard part is coming up with an appropriate name such as 'Spinplasmonics'" Elezzabi said.
Elezzabi, Abdulhakem., Physical Review Letters, volume 98, page 133901, (2007).