120 research outputs found
3D magnetization profile and multi-axes exchange bias in Co antidot arrays
Cu/Co/Cu trilayers have been deposited on nanoporous alumina membranes.
Magnetic properties of the resulting Co antidot arrays are investigated using
SQUID magnetometry. Hysteresis loops of these arrays show two-step
magnetization reversal. In addition, exchange bias is observed, whether the
cooling field is applied within or perpendicular to the surface plane. In the
former case, the exchange bias changes sign close to the blocking temperature,
and becomes positive. We attribute these effects to the local, crescent shape
of the Co films, induced by the surface morphology of the alumina membranes.
This morphology leads to a three-dimensional magnetization distribution at the
nanoscale.Comment: 3 pages, 3 figure
Ground-State Candidate for the Dipolar Kagome Ising Antiferromagnet
We have investigated the low-temperature thermodynamic properties of the
dipolar kagome Ising antiferromagnet using at-equilibrium Monte Carlo
simulations, in the quest for the ground-state manifold. In spite of the
limitations of a single spin-flip approach, we managed to identify certain
ordering patterns in the low-temperature regime and we propose a candidate for
this unknown state. This novel configuration presents some intriguing features
and passes several test-criteria, making it a very likely choice for the
dipolar long-range order of this kagome Ising antiferromagnet.Comment: 8 pages, 5 figure
Competing interactions in artificial spin chains
The low-energy magnetic configurations of artificial frustrated spin chains
are investigated using magnetic force microscopy and micromagnetic simulations.
Contrary to most studies on two-dimensional artificial spin systems where
frustration arises from the lattice geometry, here magnetic frustration
originates from competing interactions between neighboring spins. By tuning
continuously the strength and sign of these interactions, we show that
different magnetic phases can be stabilized. Comparison between our
experimental findings and predictions from the one-dimensional Anisotropic
Next-Nearest-Neighbor Ising (ANNNI) model reveals that artificial frustrated
spin chains have a richer phase diagram than initially expected. Besides the
observation of several magnetic orders and the potential extension of this work
to highly-degenerated artificial spin chains, our results suggest that the
micromagnetic nature of the individual magnetic elements allows observation of
metastable spin configurations.Comment: 5 pages, 4 figure
X-ray photoelectron emission microscopy in combination with x-ray magnetic circular dichroism investigation of size effects on field-induced N\'eel-cap reversal
X-ray photoelectron emission microscopy in combination with x-ray magnetic
circular dichroism is used to investigate the influence of an applied magnetic
field on N\'eel caps (i.e., surface terminations of asymmetric Bloch walls).
Self-assembled micron-sized Fe(110) dots displaying a moderate distribution of
size and aspect ratios serve as model objects. Investigations of remanent
states after application of an applied field along the direction of N\'eel-cap
magnetization give clear evidence for the magnetization reversal of the N\'eel
caps around 120 mT, with a 20 mT dispersion. No clear correlation could be
found between the value of the reversal field and geometrical features of the
dots
Third type of domain wall in soft magnetic nanostrips
Magnetic domain walls (DWs) in nanostructures are low-dimensional objects
that separate regions with uniform magnetisation. Since they can have different
shapes and widths, DWs are an exciting playground for fundamental research, and
became in the past years the subject of intense works, mainly focused on
controlling, manipulating, and moving their internal magnetic configuration. In
nanostrips with in-plane magnetisation, two DWs have been identified: in thin
and narrow strips, transverse walls are energetically favored, while in thicker
and wider strips vortex walls have lower energy. The associated phase diagram
is now well established and often used to predict the low-energy magnetic
configuration in a given magnetic nanostructure. However, besides the
transverse and vortex walls, we find numerically that another type of wall
exists in permalloy nanostrips. This third type of DW is characterised by a
three-dimensional, flux closure micromagnetic structure with an unusual length
and three internal degrees of freedom. Magnetic imaging on
lithographically-patterned permalloy nanostrips confirms these predictions and
shows that these DWs can be moved with an external magnetic field of about 1mT.
An extended phase diagram describing the regions of stability of all known
types of DWs in permalloy nanostrips is provided.Comment: 19 pages, 7 figure
Chiral nature of magnetic monopoles in artificial spin ice
Micromagnetic properties of monopoles in artificial kagome spin ice systems
are investigated using numerical simulations. We show that micromagnetics
brings additional complexity into the physics of these monopoles that is, by
essence, absent in spin models: besides a fractionalized classical magnetic
charge, monopoles in the artificial kagome ice are chiral at remanence. Our
simulations predict that the chirality of these monopoles can be controlled
without altering their charge state. This chirality breaks the vertex symmetry
and triggers a directional motion of the monopole under an applied magnetic
field. Our results also show that the choice of the geometrical features of the
lattice can be used to turn on and off this chirality, thus allowing the
investigation of chiral and achiral monopoles.Comment: 10 pages, 4 figure
Phase diagram of magnetic domain walls in spin valve nano-stripes
We investigate numerically the transverse versus vortex phase diagram of
head-to-head domain walls in Co/Cu/Py spin valve nano-stripes (Py: Permalloy),
in which the Co layer is mostly single domain while the Py layer hosts the
domain wall. The range of stability of the transverse wall is shifted towards
larger thickness compared to single Py layers, due to a magnetostatic screening
effect between the two layers. An approached analytical scaling law is derived,
which reproduces faithfully the phase diagram.Comment: 4 page
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