7 research outputs found
dc magnetometry of niobium thin film superconductors deposited using high power impulse magnetron sputtering
We performed a systematic investigation of the dc magnetic properties of superconducting niobium thin
films deposited by high power impulse magnetron sputtering (HiPIMS) as a function of the main deposition parameters: the temperature, T, of the heated substrate and the applied dc bias voltage, V, during the sputtering process. The measured dc magnetization curves between 0 and 1000 mT were used to calculate the relative volume of each sample into which the applied magnetic field had penetrated, ðΔV=VÞM. The sample deposited at 700°C with −80 V biased substrate exhibited the least penetration by the magnetic field. ðΔV=VÞM appeared to be highly dependent on the bias voltage at both room temperature and 500°C; however, a broad range of bias voltages showed comparatively similar results at increased temperatures of 700°C. Samples deposited at 700°C exhibit smaller upper critical fields, HC2, than samples deposited at room temperature and 500°C, with the lower temperatures exhibiting a greater dependency on the applied bias. The films deposited at 700°C also display a more stable magnetization curve suggesting that an enhanced flux pinning was achieved when compared to lower temperatures. Consequently, films with stable pinning were found to have the most repeatable dc magnetic behavior. Our results are particularly relevant to the superconducting radio-frequency accelerator scientific community where thin films have been suggested as a technology which may ultimately surpass the performance of bulk niobium. They are also relevant to the fundamental area of superconducting thin films and any applied area where thin films produced by HiPIMS are used, such as superconducting electronics
Spin Seebeck effect in polycrystalline yttrium iron garnet pellets prepared by the solid-state method [Letter]
We study the properties of polycrystalline bulk yttrium iron garnet (YIG) pellets
prepared by the solid-state method, where the choice of the sintering temperature can lead to
mixed phases of yttrium iron perovskite (YIP) and YIG or single phase YIG. Magnetometry
shows multiple switching regimes in the mixed-phase pellets where the saturation magnetization
is dominated by the proportion of YIG present. Ferromagnetic resonance was used to corroborate
the saturation magnetization from magnetometry and to extract the spin wave damping α. The
lowest damping was observed for the YIG pellet, which resulted in a spin Seebeck effect (SSE)
coefficient that was approximately 55% of single crystal YIG. This demonstrates that macroscale
crystallization does not play a major role in the SSE and paves the way for utilising polycrystalline
samples for thermomagnetic applications
DC magnetism of Niobium thin films
Niobium thin films were deposited onto a-plane sapphire with varying kinetic energy and varying substrate temperature. There were no consistent trends which related the particle energy or substrate temperature to RRR. The sample which displayed the largest RRR of 229 was then compared to both a thin film deposited with similar conditions onto copper substrate and to bulk niobium. DC magnetometry measurements suggest that the mechanism of flux entry into thin film niobium and bulk niobium may vary due to differences in the volumes of both defects and impurities located within the grains. Results also suggest that magnetic flux may penetrate thin films at small fields due to the sample geometry
Physical vapour deposition of thin films for use in superconducting RF cavities
The production of superconducting coatings for radio
frequency cavities is a rapidly developing field that
should ultimately lead to acceleration gradients greater
than those obtained by bulk Nb RF cavities. Optimizing
superconducting properties of Nb thin-films is therefore
essential. Nb films were deposited by magnetron
sputtering in pulsed DC mode onto Si (100) and MgO
(100) substrates and also by high impulse magnetron
sputtering (HiPIMS) onto Si (100), MgO (100) and
polycrystalline Cu. The films were characterised using
scanning electron microscopy, x-ray diffraction and DC
SQUID magnetometry
Development of thin films for superconducting RF cavities
Superconducting coatings for superconducting radio frequency (SRF) cavities is an intensively developing field that should ultimately lead to acceleration gradients better than those obtained by bulk Nb RF cavities. ASTeC has built and developed experimental systems for superconducting thin-film deposition, surface analysis and measurement of Residual Resistivity Ratio (RRR). Nb thin-films were deposited by magnetron sputtering in DC or pulsed DC mode (100 to 350 kHz with 50% duty cycle) with powers ranging from 100 to 600 W at various temperatures ranging from room temperature to 800 °C on Si (100) substrates. The first results gave RRR in the range from 2 to 22 with a critical temperature Tc ≈ 9.5 K. Scanning electron microscopy (SEM), x-ray diffraction (XRD), electron back scattering diffraction (EBSD) and DC SQUID magnetometry revealed significant correlations between the film structure, morphology and superconducting properties
Physical vapour deposition of NbTiN thin films for superconducting RF cavities.
The production of superconducting coatings for radio frequency (RF) cavities is a rapidly developing field that should ultimately lead to acceleration gradients greater than those obtained by bulk Nb RF cavities. The use of thin
films made from superconductors with thermodynamic critical field, Hc > HC(Nb), allows the possibility of multilayer superconductor – insulator – superconductor (SIS) films and accelerators that could operate at temperatures above 2 K. SIS films theoretically allow increased acceleration gradient due to magnetic shielding
of underlying superconducting layers [1] and higher operating temperature can reduce cost [2]. High impulse magnetron sputtering (HiPIMS) and pulsed DC magnetron sputtering processes were used to deposit NbTiN thin films onto Si(100) substrate. The films were characterised using scanning electron microscopy (SEM), x-ray diffraction (XRD), Rutherford back-scattering spectroscopy (RBS)
and a four-point probe
High power impulse magnetron sputtering of thin films for superconducting RF cavities
The production of superconducting coatings for radio
frequency cavities is a rapidly developing field that
should ultimately lead to acceleration gradients greater
than those obtained by bulk Nb RF cavities. The use of
thin films made from superconductors with
thermodynamic critical field, Hc>Hn/cb, allows the
possibility of multilayer superconductor – insulator –
superconductor (SIS) films and also accelerators that
could operate at temperatures above the 2 K typically
used. SIS films theoretically allow increased acceleration
gradient due to magnetic shielding of underlying
superconducting layers [1] and higher operating
temperature can reduce cost [2]. High impulse magnetron
sputtering (HiPIMS) and pulsed DC magnetron sputtering
processes were used to deposit NbN and NbTiN thin films
onto Si(100) substrate. The films were characterised using
scanning electron microscopy (SEM), x-ray diffraction
(XRD), Rutherford back-scattering spectroscopy (RBS)
and a four point probe