We report the evolution of magnetic moment as well as magnetic anisotropy with crystalline order in Co 2 MnSi thin films grown on (100) MgO by pulsed laser deposition. The films become more ordered as the annealing temperature (T A ) increases from 400 to 600 C. The extent of L2 1 ordering in the films annealed at 600 C is %96%. The static magnetization measurements by vibrating sample magnetometry shows a maximum moment of 4.95 l B per formula unit with low coercivity (H C % 65 Oe) in the films annealed at 600 C. A rigorous analysis of the azimuthal and polar angle dependent ferromagnetic resonance (FMR) measured at several temperatures allows determination of various anisotropy fields relevant to our system as a function of T A . Finally, we have evaluated the exchange stiffness constant down to 100 K using spin wave modes in FMR spectra. We have also estimated the exchange energies as well as stiffness constant by ab initio calculations using the Korringa-Kohn-Rostoker method. a) Electronic addresses: rcb@iitk.ac.in and rcb@nplindia.org.

We report the superconducting properties of the tungsten (W) nanowires fabricated using focussed ion beam (FIB) technique having different wire widths of ∼120 nm and ∼290 nm. The transport properties of these wires were measured down to a temperature of 20 mK in a dilution refrigerator. We observed hysteretic current- voltage characteristics (IVCs) as a function of temperature, wherein the extend of hysteresis (difference between switching current and re-trapping current) is larger at lower temperature and diminishes near to the transition temperature. The temperature dependence of the switching current and re-trapping current were analysed using conventional models and found out to be of reasonable agreement with the models invoked. The re-trapping current agrees well with the thermal model incorporating phonon contribution in the heat dissipation process along with the electronic contribution. The equilibrium electron temperature calculated using the heat dissipation models at the critical current of the wires agrees well with respect to the transition temperature of the wire having a larger width, while for the wire of lower width, it is slightly elevated. Based on the analysis, it is believed that heat dissipation primarily because of Joule heating is the cause of the hysteretic current voltage characteristics of the nanowires.

We report on Boron diffusion and subsequent crystallization of Co40Fe40B20 (CoFeB) thin films on SiO2/Si(001) substrate using pulsed laser deposition. Secondary ion mass spectroscopy reveals Boron diffusion at the interface in both amorphous and crystalline phase of CoFeB. High-resolution transmission electron microscopy reveals a small fraction of nano-crystallites embedded in the amorphous matrix of CoFeB. However, annealing at 400°C results in crystallization of CoFe with bcc structure along (110) orientation. As-deposited films are non-metallic in nature with the coercivity (Hc) of 5Oe while the films annealed at 400°C are metallic with a Hc of 135Oe

We report the evolution of crystallographic structure, magnetic ordering and electronic transport in thin films of full-Heusler alloy Co2MnSi deposited on (001) MgO with annealing temperatures (TA). By increasing the TA from 300 • C to 600 • C, the film goes from a disordered nanocrystalline phase to B2 ordered and finally to the L21 ordered alloy. The saturation magnetic moment improves with structural ordering and approaches the Slater-Pauling value of ≈ 5.0µB per formula unit for TA = 600 • C. At this stage the films are soft magnets with coercive and saturation fields as low as ≈ 7 mT and 350 mT, respectively. Remarkable effects of improved structural order are also seen in longitudinal resistivity (ρxx) and residual resistivity ratio. A model based upon electronic transparency of grain boundaries illucidates the transition from a state of negative dρ/dT to positive dρ/dT with improved structural order. The Hall resistivity (ρxy) derives contribution from the normal scattering of charge carriers in external magnetic field, the anomalous effect originating from built-in magnetization and a small but distinct topological Hall effect in the disordered phase. The carrier concentration (n) and mobility (µ) have been extracted from the high field ρxy data. The highly ordered films are characterized by n and µ of 1.19× 10 29 m −3 and 0.4 cm 2 V −1 s −1 at room temperature. The dependence of ρxy on ρxx indicates the dominance of skew scattering in our films, which shows a monotonic drop on raising the TA. The topological Hall effect is analyzed for the films annealed at 300 • C. We find maximum topological contribution to Hall resistivity around 0.5 T while it approach to zero with increasing magnetic field. The anisotropic magnetoresistance changes its sign from positive to negative as we go from as deposited to 600 • C annealed film suggesting a gradual increase in the half-metallic character.

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