356 research outputs found
Non-adiabatic spin torque investigated using thermally activated magnetic domain wall dynamics
Using transmission electron microscopy, we investigate the thermally
activated motion of domain walls (DWs) between two positions in permalloy
(Ni80Fe20) nanowires at room temperature. We show that this purely thermal
motion is well described by an Arrhenius law, allowing for a description of the
DW as a quasi-particle in a 1D potential landscape. By injecting small
currents, the potential is modified, allowing for the determination of the
non-adiabatic spin torque: the non-adiabatic coefficient is 0.010 +/- 0.004 for
a transverse DW and 0.073 +/- 0.026 for a vortex DW. The larger value is
attributed to the higher magnetization gradients present
Observation of thermally-induced magnetic relaxation in a magnetite grain using off-axis electron holography
A synthetic basalt comprising magnetic Fe3O4 grains (~ 50 nm to ~ 500 nm in diameter) is
investigated using a range of complementary nano-characterisation techniques. Off-axis electron
holography combined with in situ heating allowed for the visualisation of the thermally-induced
magnetic relaxation of an Fe3O4 grain (~ 300 nm) from an irregular domain state into a vortex state at
550˚C, just below its Curie temperature, with the magnetic intensity of the vortex increasing on cooling
Magnetic induction mapping of magnetite chains in magnetotactic bacteria at room temperature and close to the Verwey transition using electron holography
Off-axis electron holography in the transmission electron microscope is used to record magnetic induction maps of closely spaced magnetite crystals in magnetotactic bacteria at room temperature and after cooling the sample using liquid nitrogen. The magnetic microstructure is related to the morphology and crystallography of the particles, and to interparticle interactions. At room temperature, the magnetic signal is dominated by interactions and shape anisotropy, with highly parallel and straight field lines following the axis of each chain of crystals closely. In contrast, at low temperature the magnetic induction undulates along the length of the chain. This behaviour may result from a competition between interparticle interactions and an easy axis of magnetisation that is no longer parallel to the chain axis. The quantitative nature of electron holography also allows the change in magnetisation in the crystals with temperature to be measured
Energy-level quantization in YBa2Cu3O7-x phase-slip nanowires
Significant progress has been made in the development of superconducting
quantum circuits, however new quantum devices that have longer decoherence
times at higher temperatures are urgently required for quantum technologies.
Superconducting nanowires with quantum phase slips are promising candidates for
use in novel devices that operate on quantum principles. Here, we demonstrate
ultra-thin YBa2Cu3O7-x nanowires with phase-slip dynamics and study their
switching-current statistics at temperatures below 20 K. We apply theoretical
models that were developed for Josephson junctions and show that our results
provide strong evidence for energy-level quantization in the nanowires. The
crossover temperature to the quantum regime is 12-13 K, while the lifetime in
the excited state exceeds 20 ms at 5.4 K. Both values are at least one order of
magnitude higher than those in conventional Josephson junctions based on
low-temperature superconductors. We also show how the absorption of a single
photon changes the phase-slip and quantum state of a nanowire, which is
important for the development of single-photon detectors with high operating
temperature and superior temporal resolution. Our findings pave the way for a
new class of superconducting nanowire devices for quantum sensing and
computing
Voids and Mn-rich inclusions in a (Ga,Mn)As ferromagnetic semiconductor investigated by transmission electron microscopy
Voids adjacent to both cubic (ZnS-type) and hexagonal (NiAs-type) Mn-rich
nanocrystals are characterized using aberration-corrected transmission electron
microscopy in annealed Ga0.995Mn0.005As magnetic semiconductor specimen grown
by molecular beam epitaxy. Nano-beam electron diffraction measurements suggest
that the nanocrystals exhibit deviations in lattice parameter from that of bulk
MnAs. In situ annealing inside the electron microscope is used to study the
nucleation, coalescence, and grain growth of individual nanocrystals. After
annealing at 903 K, the magnetic transition temperature of the specimen likely
to be dominated by the presence of cubic ferromagnetic nanocrystals
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