K. A. Yates

Evidence for supercurrent connectivity in conglomerate particles in NdFeAsO1−δ

Here we report the use of global and local magnetometry and Hall probe imaging to investigate the electromagnetic connectivity of the superconducting current path in the oxygen-deficient fluorine-free Nd-based oxypnictides. High resolution transmission electron microscopy and scanning electron microscopy show strongly layered crystallites, evidence for a ~5?nm amorphous oxide around individual particles, and second phase neodymium oxide which may contribute to the large paramagnetic background at high field and at high temperatures. From global magnetometry and electrical transport measurements it is clear that there is a small supercurrent flowing on macroscopic sample dimensions (mm), with a lower bound for the average (over this length scale) critical current density of the order of 103?A?cm?2. From magnetometry of powder samples and local Hall probe imaging of a single large conglomerate particle ~120??m it is clear that, on smaller scales, there is better current connectivity with a critical current density of the order of 5 ? 104?A?cm?2. We find enhanced flux creep around the second peak anomaly in the magnetization curve and an irreversibility line significantly below Hc2(T) as determined by ac calorimetry.

Flux dynamics associated with the second magnetization peak in the ironpnictide Ba1-xKxFe2As2

We report on isofield magnetic relaxation data on a single crystal of

The effect of columnar defects on the pinning properties of NdFeAsO0.85 conglomerate particles

{\text{Ba}}_{1\ensuremath{-}x}{\text{K}}_{x}{\text{Fe}}_{2}{\text{As}}_{2}

The spin polarization of CrO2 revisited

with superconducting transition temperature

Spin-polarized transport current in n-type codoped ZnO thin films measured by Andreev spectroscopy

{T}_{c}=32.7\text{ }\text{K}

Microwave surface resistance in MgB2

which exhibit the so-called fish-tail effect. A surface map of the superconducting transition temperature shows that the superconducting properties are close to homogeneous across the sample. Magnetic relaxation data,

Andreev spectroscopy of CrO2 thin films on TiO2 and Al2O3

M(t)

Evidence for nodal superconductivity in Sr2ScFePO3

, was used to obtain the activation energy

The superconducting properties of co-doped polycrystalline MgB2

U(M)

Prospects for detection of spin accumulation using submicron planar Andreev array spectroscopy

in order to study different vortex-dynamics regimes. Results of this analysis along with time-dependent measurements as a function of field and temperature extended to the reversible region of some