Spin Polarized Current in Magnetic Nanostructures

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The developments in magnetic nanostructures and future magnetoelectronic devices depend crucially on the substantial spin polarization (the difference in the number of spin-up and spin-down electrons) of the ferromagnetic layer, the ability to control the switching of the ferromagnetic component, as well as effects due to spin-polarized conduction and spin-polarized current. This proposal focuses on some of the key aspects of spin-polarized currents in magnetic nanostructures. The spin diffusion lengths in metals, semiconductors, and point-contact tunnel junctions will be measured using Point-Contact Spin Spectroscopy. The temperature dependence of spin polarization in half-metallic CrO2 and Fe3O4 will also be studied in detail. The second aspect of this proposal is the investigation of the newly discovered spin-transfer torque effects in conventional ferromagnets and half-metals. Single layers of ferromagnetic materials and multilayers made up of non-magnetic, ferromagnetic and superconducting thin films will be used for these studies. The principal investigator and two female graduate students (one of whom is an African American) will carry out the proposed research at Johns Hopkins University.In addition to their electrical charge, the transport of which forms a current in an electrical circuit, electrons can also behave as tiny magnets due to an intrinsic property called spin. Traditional electronic devices, which have propelled modern technology to the electronic age, utilize only the charge of the electron. The new generation of magnetoelectronic (or spintronic) devices manipulates both charge and spin of the electron. Instead of just electrical current, magnetoelectronic devices manipulate spin-polarized current, in which the spins of the current-carrying electrons are very much aligned. One well-known magnetoelectronic device that has already perpetrated in all our computers, is the read-heads in hard drives made using materials that have enormous magnetoresistance. The development of future magnetoelectronic devices depends crucially on how one can harness and control the spins of the electrons as they are transported through devices. One major aspect of this proposal is the development and characterization of materials that can generate copious amounts of spin-polarized current. These materials hold promise as the basic materials in magnetoelectronics in a manner similar to that of silicon in traditional electronics. Because a spin-polarized current carries both electrical current and spin current, new effects, which are absent in traditional electronic devices are observed. During this proposal period, the effects of a spin-polarized current as it propagates through magnetic nanostructures will be studied. The principal investigator has been actively recruiting women and other minority students. In particular, two female graduate students, one of whom is an African American, will work with the principal investigator in this project.