27 research outputs found
Epitaxial LaFeAsOF thin films grown by pulsed laser deposition
Superconducting and epitaxially grown LaFeAsOF thin films were successfully
prepared on (001)-oriented LaAlO3 substrates using pulsed laser deposition. The
prepared thin films show exclusively a single in-plane orientation with
epitaxial relation (001)[100] parallel to (001)[100] and a FWHM value of 1deg.
Furthermore, resistive measurement of the superconducting transition
temperature revealed a Tc90 of 25K with a high residual resistive ratio of 6.8.
The applied preparation technique, standard thin film pulsed laser deposition
at room temperature in combination with a subsequent post annealing process, is
suitable for fabrication of high quality LaFeAsO1-xFx thin films. A high upper
critical field of 76.2 T was evaluated for magnetic fields applied
perpendicular to the c-axis and the anisotropy was calculated to be 3.3
assuming single band superconductivity.Comment: 6 pages, 4 Figure
Point-contact study of ReFeAs(1-x)Fx (Re=La, Sm) superconducting films
Point-contact (PC) Andreev-reflection (AR) measurements of the
superconducting gap in iron-oxipnictide ReFeAsO_{1-x}F_x (Re=La, Sm) films have
been carried out. The value of the gap is distributed in the range 2\Delta
\simeq 5-10 meV (for Re=Sm) with a maximum in the distribution around 6 meV.
Temperature dependence of the gap \Delta(T) can be fitted well by BCS curve
giving reduced gap ratio 2\Delta /kT_c^*\simeq 3.5 (here T_c^* is the critical
temperature from the BCS fit). At the same time, an expected second larger gap
feature was difficult to resolve distinctly on the AR spectra making
determination reliability of the second gap detection questionable. Possible
reasons for this and the origin of other features like clear-cut asymmetry in
the AR spectra and current regime in PCs are discussed.Comment: 6 two-column pages, 6 figs., 26 Refs., to be published in
Superconductor Science and Technolog
Scaling behaviour of the critical current in clean epitaxial Ba(Fe1-xCox)2As2 thin films
The angular-dependent critical current density, Jc(theta), and the upper
critical field, Hc2(theta), of epitaxial Ba(Fe1-xCox)2As2 thin films have been
investigated. No Jc(theta) peaks for H || c were observed regardless of
temperatures and magnetic fields. In contrast, Jc(theta) showed a broad maximum
at theta=90 degree, which arises from intrinsic pinning. All data except at
theta=90 degree can be scaled by the Blatter plot. Hc2(theta) near Tc follows
the anisotropic Ginzburg-Landau expression. The mass anisotropy increased from
1.5 to 2 with increasing temperature, which is an evidence for multi-band
superconductivity.Comment: Accepted in Physical Review B rapid communication
Influenced of Fe buffer thickness on the crystalline quality and the transport properties of Fe/Ba(Fe1-xCox)2As2 bilayers
The implementation of an Fe buffer layer is a promising way to obtain
epitaxial growth of Co-doped BaFe2As2 (Ba-122). However, the crystalline
quality and the superconducting properties of Co-doped Ba-122 are influenced by
the Fe buffer layer thickness, dFe. The well-textured growth of the Fe/Ba-122
bilayer with dFe = 15 nm results in a high Jc of 0.45 MAcm at 12 K in
self-field, whereas a low Jc value of 61000 Acm is recorded for the
bilayer with dFe = 4 nm at the corresponding reduced temperature due to the
presence of grain boundaries
DC superconducting quantum interference devices fabricated using bicrystal grain boundary junctions in Co-doped BaFe2As2 epitaxial films
DC superconducting quantum interference devices (dc-SQUIDs) were fabricated
in Co-doped BaFe2As2 epitaxial films on (La, Sr)(Al, Ta)O3 bicrystal substrates
with 30deg misorientation angles. The 18 x 8 micro-meter^2 SQUID loop with an
estimated inductance of 13 pH contained two 3 micro-meter wide grain boundary
junctions. The voltage-flux characteristics clearly exhibited periodic
modulations with deltaV = 1.4 micro-volt at 14 K, while the intrinsic flux
noise of dc-SQUIDs was 7.8 x 10^-5 fai0/Hz^1/2 above 20 Hz. The rather high
flux noise is mainly attributed to the small voltage modulation depth which
results from the superconductor-normal metal-superconductor junction nature of
the bicrystal grain boundary
Thin Film Growth and Device Fabrication of Iron-Based Superconductors
Iron-based superconductors have received much attention as a new family of
high-temperature superconductors owing to their unique properties and distinct
differences from cuprates and conventional superconductors. This paper reviews
progress in thin film research on iron-based superconductors since their
discovery for each of five material systems with an emphasis on growth,
physical properties, device fabrication, and relevant bulk material properties.Comment: To appear in J. Phys. Soc. Jp