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Spin and Lattice Dynamics in Thin Films: From Femtoseconds to Nanoseconds.

dc.contributor.authorStoica, Vladimir Alexandruen_US
dc.date.accessioned2011-01-18T16:18:45Z
dc.date.availableNO_RESTRICTIONen_US
dc.date.available2011-01-18T16:18:45Z
dc.date.issued2010en_US
dc.date.submitteden_US
dc.identifier.urihttps://hdl.handle.net/2027.42/78913
dc.description.abstractIn this dissertation we set out to quantitatively investigate the dynamics of magnetic thin films. Specifically, we studied the spin dynamics in epitaxial metallic ferromagnets and the coupling to other degrees of freedom, such as electron and phonon excitations. Key aspects of the spin dynamics were found to occur across a wide range of temporal scales, from femtoseconds to nanoseconds. Accordingly, new instrumental and experimental tools were developed in order to address the complex behavior of the magnetization under strongly non-equilibrium conditions. A new pump-probe fiber-laser-based magnetometer was built and used to access the time-dependence of the magnetic behavior during spin wave excitation and relaxation. The performance of this instrument offers significant advantages over existing methods, including: an unusually large temporal dynamic range (150 fs-10 ns), high frequency bandwidth (~5 THz), high detection sensitivity that corresponds to a signal to noise ratio of better than 107, and fast data acquisition at kilohertz scanning rates. These instrumental capabilities allowed us to perform unprecedented studies of coherent spin waves propagating through epitaxial Fe films. The femtosecond laser pulse induces coherent magnetization dynamics indirectly via thermal excitation, resulting in magnon-electron and magneto-elastic coupling. The spin wave propagation speeds and attenuation lengths were determined during spin wave propagation and reflection at the film boundaries. Coherent spin waves with frequency less than 24 GHz, propagate at velocities < 1.3 km/s, consistent with their dispersion relation. A not well understood behavior occurs for spin waves with wavevector k~0, which are transmitted super-sonically through films of about one classical skin depth thick (1.5 μm). A major step in this work was to establish all-optical techniques for manipulation and coherent control of the magnetization vector. An optically-induced spin reorientation transition of first-order is observed for the first time, which provides a new route to ultrafast coherent magnetization switching. The switching is found to be a three-step temporal process: a coherent reorientation (~ 100 ps) is followed by a spin precession in a newly created metastable state (~ 300 ps), which evolves into a dual domain state that undergoes relaxation within ~ 2 - 4 ns.en_US
dc.format.extent4537249 bytes
dc.format.extent1373 bytes
dc.format.mimetypeapplication/pdf
dc.format.mimetypetext/plain
dc.language.isoen_USen_US
dc.subjectUltrafast Spin and Lattice Dynamics in Epitaxial Fe Filmsen_US
dc.titleSpin and Lattice Dynamics in Thin Films: From Femtoseconds to Nanoseconds.en_US
dc.typeThesisen_US
dc.description.thesisdegreenamePhDen_US
dc.description.thesisdegreedisciplineApplied Physicsen_US
dc.description.thesisdegreegrantorUniversity of Michigan, Horace H. Rackham School of Graduate Studiesen_US
dc.contributor.committeememberClarke, Royen_US
dc.contributor.committeememberGuo, Lingjieen_US
dc.contributor.committeememberOrr, Bradford G.en_US
dc.contributor.committeememberReis, Daviden_US
dc.contributor.committeememberUher, Ctiraden_US
dc.subject.hlbsecondlevelPhysicsen_US
dc.subject.hlbtoplevelScienceen_US
dc.description.bitstreamurlhttp://deepblue.lib.umich.edu/bitstream/2027.42/78913/1/vstoica_1.pdf
dc.owningcollnameDissertations and Theses (Ph.D. and Master's)


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