This paper reports an in-depth study on nanocrystalline Gd-doped ZnO thin films synthesized using versatile pulsed spray pyrolysis method and exhibit room temperature ferromagnetism. The detailed structural and microstructural studies confirm that the doped Gd ions occupy Zn sites and the peak shift can be elucidated by charge neutrality. Optical investigation shows that the Gd doping in ZnO lattice leads to a decrease in the near band edge position due to the introduction of new unoccupied states by Gd 4f electrons. The electronic structure of the Zn1−xGdxO at the O K edge shows the evolution of pre-edge spectral features similar to cuprates and manganites, and also confirms the strong hybridization of O 2p–Gd 4f/5d states. Furthermore, the Gd M5 edge provides evidence that Gd ions are in the trivalent state. Hysteresis measurements demonstrate that the Gd-doped ZnO films are magnetically anisotropic and exhibit intrinsic ferromagnetic behavior at room temperature. Higher magnetization in 3 kOe values is observed for a field applied perpendicular to the sample surface compared to the in-plane direction.

No abstract

No abstract

The high field magnetization and magnetotransport measurements are carried out to determine the critical superconducting parameters of MgB 2−x C x system. The synthesized samples are pure phase and the lattice parameter evaluation is carried out using the Rietveld refinement. The R − T͑H͒ measurements are done up to a field of 140 kOe. The upper critical field values, H c2 , are obtained from these data based on the criterion of 90% of normal resistivity, i.e., H c2 = H at which =90% N , where N is the normal resistivity, i.e., resistivity of about 40K in our case. The Werthamer-Helfand-Hohenberg prediction of H c2 ͑0͒ underestimates the critical field value even below the field up to which measurement is carried out. After this model, the Ginzburg-Landau theory is applied to the R − T͑H͒ data which not only calculate the H c2 ͑0͒ value but also determine the dependence of H c2 on temperature in the low temperature high field region. The estimated H c2 ͑0͒ = 157.2 kOe for pure MgB 2 is profoundly enhanced to 297.5 kOe for the x = 0.15 sample in MgB 2−x C x series. Magnetization measurements are done up to 120 kOe at different temperatures and the other parameters such as irreversibility field H irr and critical current density J c ͑H͒ are also calculated. The nano carbon doping results in substantial enhancement of critical parameters such as H c2 , H irr , and J c ͑H͒ in comparison to the pure MgB 2 sample.

Here we report the optimized magnetotransport properties of polycrystalline La 0.70 Ca 0.3−x Sr x MnO 3 and their composites with Ag. The optimization was carried out by varying the Sr and Ag contents simultaneously to achieve large temperature coefficient of resistance ͑TCR͒ as well as low field magnetoresistance ͑MR͒ at room temperature. Sharpest paramagnetic ͑PM͒-ferromagnetic ͑FM͒ and insulator-metal ͑IM͒ transition is observed in the vicinity of the room temperature ͑T C Ϸ 300 K Ϸ T IM ͒ for the composition La 0.70 Ca 0.20 Sr 0.10 MnO 3 :Ag 0.20 . Partial substitution of larger Sr 2+ ions at the Ca 2+ ions sites controls the magnitude of the FM and IM transition temperatures, while the Ag induces the desired sharpness in these transitions. For the optimized composition, maximum TCR and MR are tuned to room temperature ͑300 K͒ with the former being as high as 9% and the later being ϳ20% and ϳ30% at 5 and 10 kOe magnetic fields respectively. Such sharp single peak ͑TCRϳ 9%͒ at room temperature can be used for the bolometric and infrared detector applications. The achievement of large TCR and low field MR at T ϳ 300 K in polycrystalline samples is encouraging and we believe that further improvements can be achieved in thin films which by virtue of their low conduction noise are more suitable for device applications.