52 research outputs found
Effect of mixed alkali-element substitution on structural and magnetic properties of praseodymium manganites Pr0.9(Na1-xKx)0.1MnO3
The effect of cationic size mismatch at the A site at constant manganese
valence on the structural and magnetic properties of a perovskite-type
rare-earth manganate was investigated in the Pr0.9(Na1-xKx)0.1MnO3 solid
solution system (0 <= x < 1). All members of this solid solution series are
orthorhombic at room temperature, space group Pbnm. Structural refinements
using the Rietveld method show that the cell volume increases and the static
Jahn-Teller distortion decreases with increasing potassium content x. Magnetic
properties are characterized by strong positive \theta p values, and are
ascribed to a canted ferromagnetic arrangement. The high Curie constant values
in the paramagnetic regime can be explained by a magnetic cluster model of 2-3
Mn ions.Comment: Journal of Alloys and Compounds (2007) (accept\'e, sous presse
The skyrmion-bubble transition in a ferromagnetic thin film
Magnetic skyrmions and bubbles, observed in ferromagnetic thin films with
perpendicular magnetic anisotropy, are topological solitons which differ by
their characteristic size and the balance in the energies at the origin of
their stabilisation. However, these two spin textures have the same topology
and a continuous transformation between them is allowed. In the present work,
we derive an analytical model to explore the skyrmion-bubble transition. We
evidence a region in the parameter space where both topological soliton
solutions coexist and close to which transformations between skyrmion and
bubbles are observed as a function of the magnetic field. Above a critical
point, at which the energy barrier separating both solutions vanishes, only one
topological soliton solution remains, which size can be continuously tuned from
micrometer to nanometer with applied magnetic field
Contacting individual Fe(110) dots in a single electron-beam lithography step
We report on a new approach, entirely based on electron-beam lithography
technique, to contact electrically, in a four-probe scheme, single
nanostructures obtained by self-assembly. In our procedure, nanostructures of
interest are localised and contacted in the same fabrication step. This
technique has been developed to study the field-induced reversal of an internal
component of an asymmetric Bloch domain wall observed in elongated structures
such as Fe(110) dots. We have focused on the control, using an external
magnetic field, of the magnetisation orientation within N\'eel caps that
terminate the domain wall at both interfaces. Preliminary magneto-transport
measurements are discussed demonstrating that single Fe(110) dots have been
contacted.Comment: 5 page
Switching probability sub-distributions and asymmetric magnetization reversal in FePt nanostructures
International audienceThe coercive field statistics in FePt nanostructures reveals the existence of multiple switching probability sub-distributions that can be asymmetric with respect to the field orientation. Each sub-distribution is correlated with an individual magnetization reversal path whose selection cannot happen at the magnetization reversal in negative (positive) field but rather at the moment of applying the initial positive (negative) magnetic field. This serves to determine the reference magnetic state from which reversal in negative (positive) field will develop. The disappearance of the asymmetric sub-distributions upon increasing the initial magnetic field μ0Hmax supports this model. However, the sub-distributions remaining at high μ0Hmax are not necessarily those characterized by the highest coercive field. This is attributed to the fact that the initial magnetization state hierarchy and the coercive field hierarchy are essentially decorrelated
Electric-field effect on coercivity distributions in FePt magneto-electric devices
International audienceWe have investigated the contribution of stochastic thermally activated processes to the electric-field effects on coercivity in FePt. Coercive field distributions were measured under different gate voltages in solid-state field-effect structures. For low voltages a shift in the coercive field distribution can be observed, however, it is not larger than the width of the distribution. Higher oltages are needed to obtain the splitting from the negative (zero) voltage distribution allowing for the unambiguous characterization of the electric-field effect. A virtual unipolarity in the electric-field effect has been identified as a feature introduced by the dielectric layer that disappears upon annealing
Local tetragonal distortion in La_{0.7}Sr_{0.3}MnO_3 strained thin films probed by x-ray absorption spectroscopy
We report on an angular resolved X-ray Absorption Spectroscopy study of
thin films epitaxially grown by pulsed laser
deposition on slightly mismatched substrates which induce tensile or
compressive strains. XANES spectra give evidence of tetragonal distortion
within the octahedra, with opposite directions for tensile and
compressive strains. Quantitative analysis has been done and a model of
tetragonal distortion reflecting the strain has been established. EXAFS data
collected in plane for tensile substrate confirm the change in the
average bond distance and the increase of length matching with the
enlargement of the cell parameter. From these results we conclude that there is
no significant change in the angle. Our observations conflict with
the scenarios which this angle is the main driving parameter in the sensitivity
of manganite films properties to external strains and suggest that the
distortion within the octahedra plays a key role in the modification of the
transport and magnetic properties.Comment: 8 pages, 6 figure
Direct observation of Oersted-field-induced magnetization dynamics in magnetic nanostripes
We have used time-resolved x-ray photoemission electron microscopy to
investigate the magnetization dynamics induced by nanosecond current pulses in
NiFe/Cu/Co nanostripes. A large tilt of the NiFe magnetization in the direction
transverse to the stripe is observed during the pulses. We show that this
effect cannot be quantitatively understood from the amplitude of the Oersted
field and the shape anisotropy. High frequency oscillations observed at the
onset of the pulses are attributed to precessional motion of the NiFe
magnetization about the effective field. We discuss the possible origins of the
large magnetization tilt and the potential implications of the static and
dynamic effects of the Oersted field on current-induced domain wall motion in
such stripes.Comment: Published in Phys. Rev. B 83, 020406 (2011) (Rapid Communications
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