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A study on the optimization of ambient temperature growth and superconducting properties of Ti-V alloy thin films grown on SiO2-coated Si substrate is reported here. These films have been synthesized by co-sputtering of Ti and V targets, and films having different Ti concentrations were deposited to get the optimized critical temperature (TC) of thin films close to the bulk value. The maximum TC of 5.2 K has been obtained in the Ti40V60 composition, which is further increased to 6.2 K when a 10 nm thick Ti underlayer is added below the Ti-V film. GIXRD measurements confirm the formation of Ti-V alloys in the desired crystal structure. The upper critical field (HC2) of the thin films has been estimated with the help of magnetotransport measurements. The utility of Ti-V alloy thin films in superconducting radiation detection applications is ascertained., Comment: 4 pages, 6 figures

The Fe$_3$O$_4$/Si films are considered to be promising materials for THz spintronic applications due to their high temperature magnetic transition and semiconducting properties. In this article, we present the real part of the dielectric constant ($\epsilon_1$) and the optical conductivity ($\sigma_1$) of Fe$_3$O$_4$ films of different thicknesses deposited on Si substrate (Fe$_3$O$_4$/Si) in the THz range at temperatures 2- 300 K. Although the magnetization of the films with thickness $\geq$ 115 nm shows a clear change at the Verwey transition temperature T$_v$ = 121 K, their optical properties in the THz frequency range are drastically different from each other. We have shown that $\sigma_1$ is maximum and $\epsilon_1$ is minimum when the Fe$^{+2}$/Fe$^{+3}$ ratio is equal to 0.54 which is the ratio of Fe+2/Fe+3 for pure Fe$_3$O$_4$. The $\sigma_1$ reduces and $\epsilon_1$ increases at all temperatures when the Fe$^{+2}$/Fe$^{+3}$ ratio deviates from 0.54. We have shown that a slight change in the Fe$^{+2}$/Fe$^{+3}$ ratio can induce large changes in the optical properties which shall have implications in the application of the Fe3O4 films in THz spintronics., Comment: 18 pages, 6 figures

The morphological, transport and terahertz optical properties of DC magnetron sputtered granular molybdenum thin-films with nano-grains embedded in an amorphous matrix have been studied in the normal and superconducting states. The superconducting transition temperatures of these films are much higher than that of bulk molybdenum. The optical properties of these thin-films have been studied using terahertz time-domain spectroscopy. Their properties have been compared with the existing materials used for the development of radiation detectors. The resistivity of the films lies in >100 micro-Ohm-cm range which is ideal for making highly sensitive radiation detectors. The Hall measurements indicate the presence of holes as the dominant carriers with very small mean free path and mobility. In the normal state, the films are disordered bad metal but they have large superfluid density and stiffness in their superconducting state. The normal state and superconducting properties of the films are very promising for their use in cryogenic radiation detectors for microwave, terahertz, and far IR frequency ranges., Comment: 27 pages, 9 figures

We report here the structural, electrical and magnetic properties of as-cast V$_{1-x}$Zr$_x$ alloys ($x$ =0 - 0.4) at low temperatures. We observe that all the alloys undergo successive peritectic and eutectic reactions during cooling from the melt which leads to the formation of five phases, namely, a body centred cubic $\beta$-V phase, two phases with slightly different compositions having face centred cubic ZrV$_2$ structure, a hexagonal closed packed $\alpha$-Zr phase, and the $\beta$-Zr precipitates. The amount of each phase is found to be dependent on the concentration of zirconium in vanadium. The $\beta$-V and ZrV$_2$ phases show superconductivity below 5.3~K and 8.5~K respectively. We show that the critical current density is large for V-rich V$_{1-x}$Zr$_x$ alloys with $x >$ 0.1. The grain boundaries generated from the eutectic reaction, and the point defects formed due to the variation in the composition are found to be responsible for the pinning of flux lines in low and high magnetic fields respectively. Our studies reveal that the choice of the composition and the heat treatment which leads to eutectic reaction are important in improving the critical current density in this alloy system., Comment: 8 pages, 7 figures

Fe/Co bilayers were made using ion beam sputtering and then were subjected to nitrogen-ion irradiation to explore the influence of irradiation on their magnetic properties. Magnetization studies of Fe/Co bilayers along with their irradiated counterparts were then performed. The magnetization and coercivity of the as-deposited sample exhibited a two-fold uniaxial symmetry while the behavior for high temperature irradiated sample depicts a small shift in the two fold behavior. The magnetization data measured with the magnetic field perpendicular to the plane of the film exhibited a hysteresis in both the case of the irradiated sample as well as as-deposited sample. A small increase in coercivity for the irradiated sample was observed which is due to various reasons including formation of FeCo solid solution due to ion irradiation at the interface.