Abebe Bahiru Kebede

Evidence of ferrimagnetic ordering in FeMnO3 produced by mechanical alloying

Abstract Mechanical alloying of α-Fe 2 O 3 with Mn 2 O 3 is shown to produce FeMnO 3 , whose X-ray diffraction pattern fits the cubic structure (space group Ia3, lattice constant ≈9.40xa0A) identical to that of Mn 2 O 3 . Temperature variation of its magnetic susceptibility χ shows a phase transition near T c ≈40xa0K and the χ −1 versus T data for T>T c fit the variation expected for a ferrimagnet with a magnetic moment of 2.8xa0μ B per formula unit. The Mossbauer spectrum for T>T c is a doublet with quadrupole splitting ≈1xa0mm/s and isomer shift ≈0.4xa0mm/s, changing to a sextet for T c with a hyperfine field of 445xa0kOe at 16xa0K.

Silver alloys for high-temperature superconducting wire

The silver cladding for high-temperature superconducting wire can be modified for various applications by alloying. For example, for powder-in-tube wire, stiffer cladding improves the smoothness of the interface. For large coils, higher strength is needed at low temperatures to hold them together. Power applications require more resistance in the cladding. We have made a survey of the properties of alloys to check their feasibility for various applications. Alloys with several elements added to silver have been prepared and evaluated for hardness, electrical properties, and compatibility with high-temperature superconductors during processing.

Studies of the correlated electron system SmB6

We have prepared high-quality, single crystals of SmB 6 under various conditions to improve sample quality. We have measured the resistivity and magnetic susceptibility from room to liquid-helium temperatures to sort samples. We have applied pulsed magnetic fields as high as 50 T at temperatures as low as 40 mK while measuring resistivity. Our samples are of higher quality than previously known. All solvent-grown, single-crystal samples should be etched to remove a surface conductivity.

The energy gap of SmB6 at low temperatures and in high magnetic fields

We have studied the energy gap of the Kondo Insulator SmB6 by means of transverse magnetoresistance measurements at temperatures down to 40mK and in magnetic fields to 50T. At 40 mK an inflection, point in the transverse magnetoresistance is observed near 35T which may indicate the closing of the gap and the onset of closed orbits.