413 research outputs found
On the reorientation transition of ultra-thin Ni/Cu(001) films
The reorientation transition of the magnetization of ferromagnetic films is
studied on a microscopic basis within a Heisenberg spin model. Using a modified
mean field formulation it is possible to calculate properties of magnetic thin
films with non-integer thicknesses. This is especially important for the
reorientation transition in Ni/Cu(001), as there the magnetic properties are a
sensitive function of the film thickness. Detailed phase diagrams in the
thickness-temperature plane are calculated using experimental parameters and
are compared with experimental measurements by Baberschke and Farle (J. Appl.
Phys. 81, 5038 (1997)).Comment: 7 pages(LaTeX2e) with one figure(eps), accepted for publication in
JMMM. See also http://www.thp.Uni-Duisburg.DE/Publikationen/Publist_Us_R.htm
Ferromagnetic resonance in systems with competing uniaxial and cubic anisotropies
We develop a model for ferromagnetic resonance in systems with competing
uniaxial and cubic anisotropies. This model applies to (i) magnetic materials
with both uniaxial and cubic anisotropies, and (ii) magnetic nanoparticles with
effective core and surface anisotropies; We numerically compute the resonance
frequency as a function of the field and the resonance field as a function of
the direction of the applied field for an arbitrary ratio of cubic-to-uniaxial
anisotropy. We also provide some approximate analytical expressions in the case
of weak cubic anisotropy. We propose a method that uses these expressions for
estimating the uniaxial and cubic anisotropy constants, and for determining the
relative orientation of the cubic anisotropy axes with respect to the crystal
principle axes. This method is applicable to the analysis of experimental data
of resonance type measurements for which we give a worked example of an iron
thin film with mixed anisotropy.Comment: 7 pages, 3 figure
ORIENTATED FePt NANOCRYSTALS DEPOSITED ON POROUS SILICON
FePt nanocrystals with L10 chemical order have high magnetic anisotropy. To form the hard magnetic L10 phase as prepared fcc FePt nanocrystals need to be heated to 600°C. We demonstrate that the morphology of chemically etched porous silicon (PS) substrates and the presence of a magnetic field during the annealing process (600 °C, 1 h) affect the particle arrangement and orientation. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) show the presence of the L10 ordered FePt particles (average diameter 15 nm) uniformly distributed on the substrate. The presence of perpendicular magnetic field during annealing increases the order parameter degree of L10 FePt NPs. These effects can be investigated from variations of the XRD peaks intensity ratio. Presence of magnetic field of 20mT in the perpendicular direction to the substrate surface increases the (001) peak intensity ratio with respect to (111) peak from 0.27 to 0.58. This effect is due to the superlattice formation at (001) direction
Continuous spin reorientation in antiferromagnetic films
We study anisotropic antiferromagnetic one-layer films with dipolar and
nearest-neighbor exchange interactions. We obtain a unified phase diagram as a
function of effective uniaxial D_e and quadrupolar C anisotropy constants. We
study in some detail how spins reorient continuously below a temperature T_s as
T and D_e vary.Comment: 3 LaTeX pages, 3 eps figures. Submitted to JMMM on 25 May 2006.
Accepted on 21 July 200
Direct visualization of dynamic magnetic coupling in a Co/Py bilayer with picosecond and nanometer resolution
We present a combination of ferromagnetic resonance (FMR) with spatially and
time-resolved X-ray absorption spectroscopy in a scanning transmission X-ray
microscope (STXM-FMR). The transverse high frequency component of the
resonantly excited magnetization is measured with element-specifity in a
Permalloy (Py) disk - Cobalt (Co) stripe bilayer microstructure. STXM-FMR
mappings are snapshots of the local magnetization-precession with nm spatial
resolution and ps temporal resolution. We directly observe the transfer of
angular momentum from Py to Co and vice versa at their respective
element-specific resonances. A third resonance could be observed in our
experiments, which is identified as a coupled resonance of Py and Co.Comment: Version submitted to Physical Review Applied with updated author list
and supplemental information (Ancillary file
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