240 research outputs found
Dynamics of Vortex Nucleation in Nanomagnets with Broken Symmetry
We investigate fundamental processes that govern dynamics of vortex
nucleation in sub-100 nm mesoscopic magnets. We focus on a structure with
broken symmetry - Pacman-like nanomagnet shape - in which we study
micromagnetic behavior both by means of a simple model and numerically. We show
that it is possible to establish desired vortex chirality and polarity by
applying only quasi-static in-plane magnetic field along specific directions.
We identify the modes of vortex nucleation that are very robust against
external magnetic field noise. These vortex nucleation modes are common among
wide range of sub-100 nm magnets with broken rotational symmetry.Comment: 5 pages, 4 figure
Evidence of Vortex Jamming in Abrikosov Vortex Flux Flow Regime
We report on dynamics of non-local Abrikosov vortex flow in mesoscopic
superconducting Nb channels. Magnetic field dependence of the non-local voltage
induced by the flux flow shows that vortices form ordered vortex chains.
Voltage asymmetry (rectification) with respect to the direction of vortex flow
is evidence that vortex jamming strongly moderates vortex dynamics in
mesoscopic geometries. The findings can be applied to superconducting devices
exploiting vortex dynamics and vortex manipulation, including superconducting
wires with engineered pinning centers.Comment: 5 pages, 3 figure
Transverse instabilities of multiple vortex chains in superconductor-ferromagnet bilayers
Using scanning tunneling microscopy and Ginzburg-Landau simulations we
explore vortex configurations in magnetically coupled NbSe-Permalloy
superconductor-ferromagnet bilayer. The Permalloy film with stripe domain
structure induces periodic local magnetic induction in the superconductor
creating a series of pinning-antipinning channels for externally added magnetic
flux quanta. Such laterally confined Abrikosov vortices form quasi-1D arrays
(chains). The transitions between multichain states occur through propagation
of kinks at the intermediate fields. At high fields we show that the system
becomes non-linear due to a change in both the number of vortices and the
confining potential. The longitudinal instabilities of the resulting vortex
structures lead to vortices `levitating' in the anti-pinning channels.Comment: accepted in PRB-Rapid
Self-assembly routes towards creating superconducting and magnetic arrays
Using self-assembly from colloidal suspensions of polystyrene latex spheres we prepared well-ordered templates. By electrochemical deposition of magnetic and superconducting metals in the pores of such templates highly ordered magnetic and superconducting anti-dot nano-structures with 3D architectures were created. Further developments of this template preparation method allow us to obtain dot arrays and even more complicated structures. In magnetic anti-dot arrays we observe a large increase in coercive field produced by nanoscale (50–1000nm) holes. We also find the coercive field to demonstrate an oscillatory dependence on film thickness. In magnetic dot arrays we have explored the genesis of 3D magnetic vortices and determined the critical dot size. Superconducting Pb anti-dot arrays show pronounced Little-Parks oscillations in Tc and matching effects in magnetization and magnetic susceptibility. The spherical shape of the holes results in significantly reduced pinning strength as compared to standard lithographic samples. Our results demonstrate that self-assembly template methods are emerging as a viable, low cost route to prepare sub-micron structures
The chiral phase transition in charge ordered 1T-TiSe2
It was recently discovered that the low temperature, charge ordered phase of
1T-TiSe2 has a chiral character. This unexpected chirality in a system
described by a scalar order parameter could be explained in a model where the
emergence of relative phase shifts between three charge density wave components
breaks the inversion symmetry of the lattice. Here, we present experimental
evidence for the sequence of phase transitions predicted by that theory, going
from disorder to non-chiral and finally to chiral charge order. Employing X-ray
diffraction, specific heat, and electrical transport measurements, we find that
a novel phase transition occurs ~7 K below the main charge ordering transition
in TiSe2, in agreement with the predicted hierarchy of charge ordered phases.Comment: 5 pages, 3 figures; includes additional experimental and theoretical
results; fixed typo
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