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Amorphous Ge1−xMnx thin films have been prepared by co-depositing Ge and Mn on SiO2/Si using an ultrahigh vacuum molecular beam epitaxy system. Across a range of growth temperatures and Mn concentrations (2.8 at. %, 10.9 at. %, and 21.3 at. %), we achieved enhanced magnetic and electrical properties with non-magnetic codopants dispersed in the films. Self-assembled Mn-rich amorphous nanostructures were observed in the amorphous Ge matrix, either as isolated nanoclusters or as nanocolumns, depending on Mn concentration. The ferromagnetic saturation moments were found to increase with Mn concentration and reached a maximum of 0.7 μB/Mn in the as-grown samples. Two magnetic transition temperatures around 15 K and 200 K were observed in these amorphous MBE-grown samples. Coercivity is considered within the context of local magnetic anisotropy. The anomalous Hall effect confirmed a strong correlation between the magnetization and transport properties, indicating that global ferromagnetic coupling was carrier-m...

In this study, ferromagnetic MnAl films were prepared by alternating Al/Mn quasi-monolayer deposition using a novel biased target ion beam deposition (BTIBD) technique. XRD results showed that the magnetic τ phase was well formed in MnAl thin films (∼10 nm), which grew epitaxially on single crystal MgO (001) substrates. The optimized saturation magnetization was ∼394 emu/cc. Furthermore, we observed a thickness-dependent uniaxial anisotropy in ferromagnetic MnAl films, which was attributed to the change of the tetragonal lattice distortion as a function of film thickness. The relationship between the film thicknesses and saturation magnetizations suggested the existence of a magnetically dead layer ∼2.7 nm with an extrapolated saturation moment around 523 emu/cc (∼1.90 μB/Mn). This value has exceeded the experimental value in bulk materials and is close to the theoretically predicted magnetization (∼1.975 μB/Mn).

Ge1−xMnx thin films with an average Mn concentration of 0.64 at. % were fabricated through Mn ion implantation into crystalline germanium-on-insulator wafers. Implantation damage was removed and crystallinity restored by pulsed laser melting from a single 30-ns 308-nm XeCl+ excimer laser pulse. Resolidified films demonstrated higher Curie temperatures but smaller saturation magnetizations than those of both as-implanted films and implanted films subjected to rapid thermal annealing. These findings are attributed to the redistribution of Mn during solidification.

The metal-insulator transition (MIT) in vanadium dioxide in the vicinity of room temperature makes it one of the most interesting materials for novel switching device applications. It is therefore essential to have a fundamental understanding of the VO2 surface when it is incorporated into multilayer structures or nanodevices. This study focuses on the surface modification of VO2 in response to the thermal treatment during phase transition. Vacuum annealing at temperatures in the vicinity of the MIT triggers a partial reduction in the surface, and thus initiates a chemical phase transition. Scanning tunneling microscopy and spectroscopy are used to investigate the electronic properties and surface structure of the VO2 thin film on (0001) sapphire substrates. Band gap maps with a high spatial resolution and single point spectroscopy I-V curves are measured as the sample is cycled through the MIT, and thus provide a direct observation of the surface phase transition at the nanoscale. The VO2 surface exhibit...

We introduced 1.1 at. % of Mn ions into Ge thin films in order to explore the ferromagnetism in Mn implanted Ge. Rapid thermal anneal (RTA) was applied after the implantation to recrystallize the Ge and enhance the incorporation of Mn ions into the Ge lattice. A maximum saturation moment of 0.7 μB/Mn at 5 K was reached when the sample was annealed at 300 °C for 1 min, and the moment decreased with higher annealing temperatures. Two transitions temperatures Tc and Tcl were observed corresponding to the global ferromagnetism in Mn:Ge bulk and short range magnetic ordering in Mn-rich clusters. Both critical temperatures increased with RTA temperatures and Tcl even persisted close to room temperature for the 400 °C, 1 min anneal. No secondary phases were observed.

Vanadium dioxide is investigated as potential oxide barrier in spin switches, and in order to incorporate VO2 layers in complex multilayer devices, it is necessary to understand the relation between bulk and surface/interface properties. Highly oriented VO2 thin films were grown on (0001) sapphire single crystal substrates with reactive bias target ion beam deposition. In the analysis of the VO2 films, bulk-sensitive methods [x-ray diffraction (XRD) and transport measurements] and surface sensitive techniques [photoelectron spectroscopy (PES) and scanning tunneling microscopy and spectroscopy] were employed. The samples were subjected to heating cycles with annealing temperatures of up to 425 and 525K. Prior to annealing the VO2 films exhibit the transition from the monoclinic to the tetragonal phase with the concurrent change in conductivity by more than a factor of 103 and their phase purity is confirmed by XRD. Annealing to 425K and thus cycling across the metal-insulator transition (MIT) temperature h...