68 research outputs found
Numerical simulation of magnetization process in antiferromagnetic ferromagnetic bilayer with compensated interface
The properties of antiferromagnetic ferromagnetic bilayer have been studied
using self-consistent mean-field approximation for Heisenberg Hamiltonian. The
perpendicular exchange coupling has been revealed in a bilayer with a
compensated interface. For a uniform antiferromagnetic film a symmetrical
hysteresis loop has been calculated, because the transverse instability
develops within the antiferromagnetic film at certain critical value of
external magnetic field. On the other hand, shifted hysteresis loop with a
finite exchange bias field has been obtained for a non-uniform
antiferromagnetic film consisting of various domains with perpendicular
directions of the easy anisotropy axes.Comment: 6 pages, 4 figure
Magnetization reversal process and nonlinear magneto-impedance in Cu/NiFe and Nb/NiFe composite wires
The magnetization reversal of Cu/NiFe and Nb/NiFe composite wires carrying AC
current is studied. The frequency spectrum of a voltage induced in a pick-up
coil wound around the wire is analyzed. The frequency spectrum is shown to
consist of even harmonics within a wide range of AC current amplitudes and
longitudinal DC magnetic fields. The strong dependencies of the harmonic
amplitudes on the DC field are found. The results obtained may be of importance
for the design of weak magnetic field sensors.Comment: 8 pages, 4 figures, publishe
Modeling of torsion stress giant magnetoimpedance in amorphous wires with negative magnetostriction
A model describing the influence of torsion stress on the giant
magnetoimpedance in amorphous wires with negative magnetostriction is proposed.
The wire impedance is found by means of the solution of Maxwell equations
together with the Landau-Lifshitz equation, assuming a simplified spatial
distribution of the magnetoelastic anisotropy induced by the torsion stress.
The impedance is analyzed as a function of the external magnetic field, torsion
stress and frequency. It is shown that the magnetoimpedance ratio torsion
dependence has an asymmetric shape, with a sharp peak at some value of the
torsion stress. The calculated field and stress dependences of the impedance
are in qualitative agreement with results of the experimental study of the
torsion stress giant magnetoimpedance in Co-based amorphous wires.Comment: 17 pages, 5 figure
Modeling of asymmetric giant magnetoimpedance in amorphous ribbons with a surface crystalline layer
A model describing the asymmetric giant magnetoimpedance (GMI) in
field-annealed amorphous ribbons is proposed. It is assumed that the ribbon
consists of an inner amorphous core and surface hard magnetic crystalline
layers. The model is based on a simultaneous solution of linearizied Maxwell
equations and Landau-Lifshitz equation. The coupling between the surface layers
and the amorphous core is described in terms of an effective bias field.
Analytical expressions for the frequency and field dependences of the ribbon
impedance are found. The calculated dependences are in a qualitative agreement
with results of experimental studies of the high-frequency asymmetric giant GMI
in field-annealed amorphous ribbons.Comment: 13 pages, 3 figure
Current distribution and giant magnetoimpedance in composite wires with helical magnetic anisotropy
The giant magnetoimpedance effect in composite wires consising of a
non-magnetic inner core and soft magnetic shell is studied theoretically. It is
assumed that the magnetic shell has a helical anisotropy. The current and field
distributions in the composite wire are found by means of a simultaneous
solution of Maxwell equations and the Landau-Lifshitz equation. The expressions
for the diagonal and off-diagonal impedance are obtained for low and high
frequencies. The dependences of the impedance on the anisotropy axis angle and
the shell thickness are analyzed. Maximum field sensitivity is shown to
correspond to the case of the circular anisotropy in the magnetic shell. It is
demonstrated that the optimum shell thickness to obtain maximum impedance ratio
is equal to the effective skin depth in the mahnetic material.Comment: 23 pages, 7 figure
Inverse flux quantum periodicity of magnetoresistance oscillations in two-dimensional short-period surface superlattices
Transport properties of the two-dimensional electron gas (2DEG) are
considered in the presence of a perpendicular magnetic field and of a {\it
weak} two-dimensional (2D) periodic potential modulation in the 2DEG plane. The
symmetry of the latter is rectangular or hexagonal. The well-known solution of
the corresponding tight-binding equation shows that each Landau level splits
into several subbands when a rational number of flux quanta pierces the
unit cell and that the corresponding gaps are exponentially small. Assuming the
latter are closed due to disorder gives analytical wave functions and
simplifies considerably the evaluation of the magnetoresistivity tensor
. The relative phase of the oscillations in and
depends on the modulation periods involved. For a 2D modulation
with a {\bf short} period nm, in addition to the Weiss oscillations
the collisional contribution to the conductivity and consequently the tensor
show {\it prominent peaks when one flux quantum passes
through an integral number of unit cells} in good agreement with recent
experiments. For periods nm long used in early experiments, these
peaks occur at fields 10-25 times smaller than those of the Weiss oscillations
and are not resolved
Inhomogeneous States in a Small Magnetic Disk with Single-Ion Surface Anisotropy
We investigate analytically and numerically the ground and metastable states
for easy-plane Heisenberg magnets with single-ion surface anisotropy and disk
geometry. The configurations with two half-vortices at the opposite points of
the border are shown to be preferable for strong anisotropy. We propose a
simple analytical description of the spin configurations for all values of a
surface anisotropy. The effects of lattice pinning leads to appearance of a set
of metastable configurations.Comment: 10 pages, 7 figures; submitted to Phys. Rev.
Deuteron frozen spin polarized target for nd experiements at the VdG accelerator of Charles University
A frozen spin polarized deuteron target cooled by the 3He/4He dilution
refrigerator is described. Fully deuterated 1,2-propanediol was used as a
target material. Deuteron vector polarization about 40% was obtained for the
target in the shape of a cylinder of 2 cm diameter and 6 cm length. The target
is intended for a study of 3N interactions at the polarized neutron beam
generated by the Van de Graaff accelerator at the Charles University in Prague
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