66,663 research outputs found
Layer-resolved imaging of domain wall interactions in magnetic tunnel junction-like trilayers
We have performed a layer-resolved, microscopic study of interactions between
domain walls in two magnetic layers separated by a non-magnetic one, using
high-resolution x-ray photoemission electron microscopy. Domain walls in the
hard magnetic Co layer of a Co/Al2O3/FeNi trilayer with in-plane uniaxial
anisotropy strongly modify the local magnetization direction in the soft
magnetic FeNi layer. The stray fields associated to the domain walls lead to an
antiparallel coupling between the local Co and FeNi moments. For domain walls
parallel to the easy magnetization axis this interaction is limited to the
domain wall region itself. For strongly charged (head-on or tail-to-tail)
walls, the antiparallel coupling dominates the interaction over radial
distances up to several micrometers from the centre of the domain wall.Comment: Published version, J. Phys.: Condens. Matter 19, 476204 (2007
A hysteresis model with dipole interaction: one more devil-staircase
Magnetic properties of 2D systems of magnetic nanoobjects (2D regular
lattices of the magnetic nanoparticles or magnetic nanostripes) are considered.
The analytical calculation of the hysteresis curve of the system with
interaction between nanoobjects is provided. It is shown that during the
magnetization reversal system passes through a number of metastable states. The
kinetic problem of the magnetization reversal was solved for three models. The
following results have been obtained. 1) For 1D system (T=0) with the
long-range interaction with the energy proportional to , the
staircase-like shape of the magnetization curve has self-similar character. The
nature of the steps is determined by interplay of the interparticle interaction
and coercivity of the single nanoparticle. 2) The influence of the thermal
fluctuations on the kinetic process was examined in the framework of the
nearest-neighbor interaction model. The thermal fluctuations lead to the
additional splitting of the steps on the magnetization curve. 3) The
magnetization curve for system with interaction and coercivity dispersion was
calculated in mean field approximation. The simple method to experimentally
distinguish the influence of interaction and coercivity dispersion on the
magnetization curve is suggested.Comment: 22 pages, 8 figure
Direct measurement of antiferromagnetic domain fluctuations
Measurements of magnetic noise emanating from ferromagnets due to domain
motion were first carried out nearly 100 years ago and have underpinned much
science and technology. Antiferromagnets, which carry no net external magnetic
dipole moment, yet have a periodic arrangement of the electron spins extending
over macroscopic distances, should also display magnetic noise, but this must
be sampled at spatial wavelengths of order several interatomic spacings, rather
than the macroscopic scales characteristic of ferromagnets. Here we present the
first direct measurement of the fluctuations in the nanometre-scale spin-
(charge-) density wave superstructure associated with antiferromagnetism in
elemental Chromium. The technique used is X-ray Photon Correlation
Spectroscopy, where coherent x-ray diffraction produces a speckle pattern that
serves as a "fingerprint" of a particular magnetic domain configuration. The
temporal evolution of the patterns corresponds to domain walls advancing and
retreating over micron distances. While the domain wall motion is thermally
activated at temperatures above 100K, it is not so at lower temperatures, and
indeed has a rate which saturates at a finite value - consistent with quantum
fluctuations - on cooling below 40K. Our work is important because it provides
an important new measurement tool for antiferromagnetic domain engineering as
well as revealing a fundamental new fact about spin dynamics in the simplest
antiferromagnet.Comment: 19 pages, 4 figure
Disorder induced phase segregation in La2/3Ca1/3MnO3 manganites
Neutron powder diffraction experiments on La2/3Ca1/3MnO3 over a broad
temperature range above and below the metal-insulator transition have been
analyzed beyond the Rietveld average approach by use of Reverse Monte Carlo
modelling. This approach allows the calculation of atomic pair distribution
functions and spin correlation functions constrained to describe the observed
Bragg and diffuse nuclear and magnetic scattering. The results evidence phase
separation within a paramagnetic matrix into ferro and antiferromagnetic
domains correlated to anistropic lattice distortions in the vicinity of the
metal-insulator transition.Comment: 3 pages, 4 figures. Submitted to Phys. Rev. Lett. Figure 1 replace
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