Novel Half-Metallic and Spin-Gapless Heusler Compounds
Thesis Defense
3:00 pm
Jorgensen Hall Room: 245
Yunlong Jin, Ph.D.
Advisor: David J. Sellmyer
Abstract:
Half-metallic and spin-gapless Heusler compounds present an interesting class of ferromagnetic materials for spintronic applications since they are predicted to be 100 % spin polarization at the Fermi level. In this thesis, the structural, magnetic, spin-polarization and electron-transport properties of the fabricated Heusler compounds and alloys CoFeCrAl, Mn2PtSn and CoFeCrX (X = Si, Ge) were studied. CoFeCrAl thin films deposited on MgO exhibit nearly perfect epitaxy and a high degree of L21 Heusler order. The effect of the different types of chemical disorder on the spin-gapless semiconductivity of CoFeCrAl was investigated. The transport spin polarization at the Fermi level is higher than 68% and probably exceeds 90%. Epitaxial thin films of inverse tetragonal Mn2PtSn were also synthesized with lattice constants a = 0.449 nm, and b = 0.615 nm. Magnetization measurements revealed an in-plane anisotropy energy of 10.0 Merg/cm3. CoFeCrSi and CoFeCrGe Heusler compounds crystallize in the cubic L21 structures with partial disorder. The CoFeCrSi alloy exhibited a high Curie temperature (TC = 790 K). Cubic CoFeCrGe decomposed into other compounds near 402 oC (675 K). A new tetragonal Co53.4Fe30.4Cr8.6Ge7.6 phase with lattice parameters a = 0.760 nm, c = 0.284 nm was found and studied with a series of tilted electron-diffraction measurements in this work. The results show promise for the implementation of CoFeCrX (X = Al, Si, Ge) and Mn2PtSn in future spintronics devices.
Advisor: David J. Sellmyer
Abstract:
Half-metallic and spin-gapless Heusler compounds present an interesting class of ferromagnetic materials for spintronic applications since they are predicted to be 100 % spin polarization at the Fermi level. In this thesis, the structural, magnetic, spin-polarization and electron-transport properties of the fabricated Heusler compounds and alloys CoFeCrAl, Mn2PtSn and CoFeCrX (X = Si, Ge) were studied. CoFeCrAl thin films deposited on MgO exhibit nearly perfect epitaxy and a high degree of L21 Heusler order. The effect of the different types of chemical disorder on the spin-gapless semiconductivity of CoFeCrAl was investigated. The transport spin polarization at the Fermi level is higher than 68% and probably exceeds 90%. Epitaxial thin films of inverse tetragonal Mn2PtSn were also synthesized with lattice constants a = 0.449 nm, and b = 0.615 nm. Magnetization measurements revealed an in-plane anisotropy energy of 10.0 Merg/cm3. CoFeCrSi and CoFeCrGe Heusler compounds crystallize in the cubic L21 structures with partial disorder. The CoFeCrSi alloy exhibited a high Curie temperature (TC = 790 K). Cubic CoFeCrGe decomposed into other compounds near 402 oC (675 K). A new tetragonal Co53.4Fe30.4Cr8.6Ge7.6 phase with lattice parameters a = 0.760 nm, c = 0.284 nm was found and studied with a series of tilted electron-diffraction measurements in this work. The results show promise for the implementation of CoFeCrX (X = Al, Si, Ge) and Mn2PtSn in future spintronics devices.