R. Goswami

Electrical spin injection into Si: A comparison between Fe/Si Schottky and Fe/Al2O3 tunnel contacts

We compare electrical spin injection from Fe into Si n-i-p heterostructures using different tunnel barriers—a reversed biased Fe/Si Schottky contact and a Fe/Al2O3 barrier. The electroluminescence (EL) spectra are dominated by transverse acoustic and optical phonon emission for both types of structures. The circular polarization of the EL tracks the Fe magnetization, confirming that the spin-polarized electrons originate from the Fe in each case. However, the polarization is lower for the Fe/Si contact than for the Fe/Al2O3 contact. Transmission electron microscopy reveals a complex interface and intermixing for Fe/Si that is absent in Fe/Al2O3/Si.

Growth of ferromagnetic nanoparticles in Ge:Fe thin films

The microstructure and magnetic properties of Ge:Fe thin films grown by molecular-beam epitaxy have been studied by transmission electron microscopy and superconducting quantum interference device magnetometry. Films were deposited on GaAs(001) at substrate temperatures (TS) ranging from 70to400°C. Nanoparticles of ferromagnetic Fe3Ge2 form in a single-crystalline Ge matrix for TS⩾150°C. The evolution of magnetic order has been evaluated as the particle size increases from 2nm at TS=150°C to 15nm at 400°C. The ferromagnetic order of Ge:Fe nanocomposite thin films originates solely from ferromagnetic second-phase particles.

Fatigue-Assisted Grain Growth in Al Alloys

Stress-assisted grain growth at room temperature is known for materials with nanocrystalline grains. For larger grain sizes, the grain growth usually takes place at higher homologous temperatures even under stress. Here we report, for the first time, significant grain growth at room temperature under fatigue loading in microcrystalline grains (≥10u2009μm) in Al 7075. We demonstrate that this grain growth at room temperature is similar to non-uniform grain growth due to grain rotation and coalescence rather than the thermally and the stress-assisted driven grain growth. We show that the grain growth is associated with the formation of a strong near-Cu {112}<111> texture component as a result of fatigue-assisted deformation. These changes in microstructural features (viz., grain size, grain orientations and texture) are fundamentally important in understanding the cyclic crack induced deformation behavior and for predicting the fatigue lifetime in structural materials.

Epitaxial growth of the diluted magnetic semiconductors Cr y Ge/sub 1-y/, (Cr,Mn):Ge, and Fe/sub z/Ge/sub 1-x/

The molecular beam epitaxial growth of the diluted magnetic semiconductors Cr/sub y/Ge/sub 1-y/, (Cr,Mn):Ge, and Fe/sub z/Ge/sub 1-x/ was reported and the structural, magnetic and transport properties of the samples were described.