Role of spin manifold on two magnon scattering
Using the time and spatial resolved Kerr effect we were able to study the relaxation of non zero spin wave (k~105 cm-1) in presence of the interface two magnon scattering in GaAs/Fe/Cr(001) structure. It was shown that the effective damping depends on the position of spin manifold with respect to the resonance k-wave-vector. Two magnon scattering can be entirely switched off by positioning the k wave-vector at the bottom of the spin manifold (no degenerate modes). Further details in Phys. Rev. Lett. 95, 37401 (2005)
Spin dynamics in self assembled network of misfit dislocations
It was shown that the formation of a self-assembled nano network of misfit dislocations in crystalline structures can lead to a strong extrinsic magnetic damping. The Ferromagnetic Resonance (FMR) measurements revealed that the extrinsic damping is caused by two magnon scattering. The contribution to the FMR linewidth from two magnon scattering is strongly anisotropic and follows the rectangular symmetry of the glide planes of the misfit dislocation network. The angular dependence of the Fourier components results in an effective channeling of spin waves along the misfit dislocation glide planes. Phys. Rev. B 69, 4417 (2004)
Magnetic coupling through MgO(001) using Fe whisker/MgO/Fe(001) structures
Using magneto-optical imaging we were able to study the magnetic coupling in crystalline Fe whisker/MgO/Fe(001) tunneling junctions. It was shown that the crystalline MgO(001) layers grown on Fe are inactive in interlayer magnetic coupling. The magnetic coupling between the Fe layer and Fe whisker was caused my magnetic stray fields around the domain wall of Fe whisker. The direction of the stray field (oriented perpendicular to the domain wall) switches its direction by presence of Bloch lines. The strays fields are large and explain a gradual demagnetization of hard magnetic layers in MRAM memory pixels after numerous magnetization reversal of psedo-spin valve devices. Phys.Rev. B 65, 144405 (2002)
Spin transport by spin pumping
Research interest has shifted increasingly from the static to the dynamic properties of magnetic multilayers. This is motivated by the fact that the switching time of magnetic hybrid multilayers used in mass data storage devices and magnetic random access memories (MRAM) is a real technological issue. It is currently of a considerable interest to acquire a thorough understanding of the spin dynamics in the nano-second time regime. By using high quality crystalline Fe, Au ultrathin film structures on GaAs(001) templates we found that a rotating magnetization creates a spin current in surrounding normal metal layers. This is a new effect. The precessing magnetization acts as a peristaltic spin pump which transports the spin momentum away from the ferromagnet (FM). It is important to realize that one can create the transport of spin momentum without using net electrical current. In magnetic bi-layers the second FM absorbs the spin current acting as a spin sink, and results in additional magnetic damping obeying the Gilbert phenomenology. The precessing magnetic moments feel each other by exchanging nonequilibrium spin currents through nonmagnetic spacers. This means that the magnetic relaxations are not the sole property of the individual magnetic films. They depend on surrounding magnetic layers, and that provides an additional control of the relaxation torque in magnetic multilayers. Both spin pumping and spin sink are purely quantum-mechanical effects. Y. Tserkovnyak, A. Brataas, Harvard U., and Prof. G. Bauer, Delft University simultaneously formulated a quantitative theory describing the spin pumping effect. In a collaborative effort we derived additional magnetic torques for Landau-Lifschitz eq. of motion which account for spin pumping and spin sink. We found an excellent quantitative agreement between theory and experiment, Phys. Rev. Lett. 90, 187601(2003). Using general Mori memory response function we have shown that spin pumping is the consequence of time dependent interlayer exchange coupling. Phys. Rev. B 67, 144418 (2003)
Spin injection in magnetic tunneling structures, in collaboration with Professor Kirschner, Max-Planck Institute, Halle, Germany
A simple STM system can be used to investigate the local spin injection on the lateral scale of 0.5 nm through a magnetic tunneling junction with the upper metallic electrode facing the tunneling tip. The electron transport in our studies was carried out using crystalline Fe whisker/MgO/Fe/Au(001) structures. The tunneling barrier was found to be ~3.5 eV as expected for a perfect MgO. This was the first demonstration of ballistic tunneling across a fully formed tunneling structure (the top layer is metallic). The STM technique allowed us to carry out the electron transport studies through either perfect MgO barriers or select those parts of the MgO spacer which are affected by structural defects such as misfit dislocation lines and interband defects. This work triggered a great deal of interest by theorists and subsequently specialists working in spintronics. Phys. Rev. B 64, 134411 (2001)
