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|Title:||ALS Special Seminar | Michael Koerner (Helmholtz Center Dresden/Germany)|
|When:||05/14/2012 11:00 AM - 12:00 PM|
|Description:||ALS Special Seminar|
Mon, May 14, 2012
15-253 Conf Rm
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion-Beam Physics and Materials
Research, Dresden, Germany
Morphology induced magnetic anisotropy and damping in thin films
Both, modification of magnetic anisotropy as well as damping, are of fundamental and
technological importance. When miniaturizing the dimensions of a magnetic device
roughness becomes more and more important, e.g. induced anisotropies have to be
taken into account. Additionally new effects like direction dependent, defect induced
two-magnon scattering are enabled. This opens the possibility for new types of devices
where the damping can be set by an external magnetic field or by frequency.
Broad ion beam erosion is a well-established technique for structuring large scale surfaces.
By varying the ion irradiation parameters, e.g. ion energy, fluence, incident angle,
and sample temperature sinusoidally modulated surface corrugations (ripples) can be
created with a periodicity tuneable over a wide range. Growing magnetic materials on
these rippled substrates imprints the surface corrugation to the deposited material and
induces a uniaxial magnetic anisotropy (UMA), caused by dipolar effects, where the
strength of the UMA is wavelength dependent. On the other hand the imprinted surface
corrugation can serve as spin wave scattering center in thin magnetic films, modifying
the magnetic damping properties by introducing a two-magnon scattering contribution.
The in-plane anisotropy and damping properties of magnetic films grown on rippled
substrates were investigated by means of angular as well as frequency dependent vector
network analyzer ferromagnetic resonance. In case of tailoring magnetic anisotropy,
the influence of single-crystalline thin iron films epitaxially grown on rippled MgO substrates
will be presented. Here a superposition of magneto-crystalline and morphology
induced UMA is observed, where the UMA can be set to an arbitrary direction with respect
to the crystalline anisotropy. Furthermore the influence of rippled surfaces on thin
polycrystalline Ni80Fe20 films will be discussed, where the surface corrugation acts as
spin wave scattering center introducing a two-magnon scattering damping contribution.
The latter leads to distinct peaks in the frequency dependent linewidth and a uniaxial
in-plane damping behavior.