Nam Dao

Magnetic properties and spin polarization of Ru doped half metallic CrO2

Chromium dioxide (CrO2) is a half metal that is of interest for spintronic devices. It has not been synthesized through traditional physical vapor deposition (PVD) techniques because of its thermodynamic instability in low oxygen pressures. Epitaxial thin films of Ru doped tetragonal rutile CrO2 were synthesized by a PVD technique. The as-deposited RuxCr1−xO2 was ferrimagnetic with the saturation magnetization moment showing a strong dependence on the Ru concentration. Curie temperature as high as 241 K has been obtained for ∼23 at. % Ru. The Ru substitution increased the electrical conductivity by increasing the minority spin concentration. The spin polarization was found to be as high as 70% for 9 at. % Ru and decreased to ∼60% with Ru concentrations up to ∼44 at. %, which is determined by the Fermi velocities of the majority and minority spins. First principle calculations were performed to understand the effect of Ru content on the properties of CrO2. The PVD processes of Ru doped CrO2 could lead to t...

Magneto-transport and domain wall scattering in epitaxy L10 MnAl thin film

This work demonstrated two different kinds of magneto-transport behaviors in epitaxial L10 MnAl film as a function of temperature. The magneto-resistance ratio (MR) was negative and exhibited evident enhancement in the resistivity at coercive fields above 175 K. The MR enhancement was attributed to the increase in the magnetic domain walls based on the quantitative correlation between the domain density and the resistivity. Below 175 K, the MR was positive and showed a quadratic dependence on the external magnetic field, which implied that the MR was dominated by Lorentz effects.

Surface morphology control of Nb thin films by biased target ion beam deposition

One of the many challenges for niobium (Nb) based superconducting devices is the concurrent improvement over the surface morphology without undermining superconducting properties. In this work, the authors demonstrated the modification to the surface morphology of 10–100 nm Nb thin films deposited by bias target ion beam deposition (BTIBD). Target current (IT) and target bias (VT) were the main parameters explored and were found to be critical to the control over crystallinity and surface morphology of Nb films. The optimized growth conditions yielded a ∼50 nm thick Nb film with the root-mean-square roughness of 0.4 nm, which was an order of magnitude smoother than that of Nb films by sputtering process. The critical temperature for superconductivity was close to the value of the bulk Nb (∼9.3 K) with a very homogeneous transition (the superconducting transition width ΔTc of 0.1 K). The quality of Nb film was evident in the presence of a very thin proximity layer (∼0.75 nm). The experimental results demon...