Special Heusler compounds for spintronic applications

This work emphasizes the potential of Heusler compounds in a wide range of spintronic applications. Using electronic structure calculations it is possible to design compounds for specific applications. \nExamples for GMR and TMR applications, for spin injection into semiconductors, and for spin torque transfer applications\nwill be shown. After a detailed introduction about spintronics and related materials chapter 5 reports about the investigation of new half-metallic compounds where the Fermi energy is \ntuned in the middle of the gap to result in more stable compounds for GMR and TMR applications.\nThe bulk properties of the quaternary Heusler alloy Co2Mn(1-x)Fe(x)Si with the Fe concentration ranging from x=0 to 1\nwill be reported and the results suggest that the best candidate for applications may be found at an iron concentration of about 50%.\nDue to the effect that in the Co2Mn(1-x)Fe(x)Si series the transition metal carrying the localized moment is exchanged and this might lead to unexpected effects on the magnetic properties if the samples are not completely homogeneous chapter 6 reports about the optimization of the Heusler compounds for GMR and TMR applications.\nThe structural and magnetic properties of the quaternary Heusler alloy Co2FeAl(1-x)Si(x) with varying Si concentration will be reported. From the combination of experimental (better order for high Si content) and theoretical findings (robust gap at x = 0.5) it is concluded that a compound with an intermediate Si concentration close \nto x=0.5-0.7 would be best suited for spintronic applications, especially for GMR and TMR applications.\nIn chapter 7 the detailed investigation of compounds for\nspin injection into semiconductors will be reported. \nIt will be shown that the diluted magnetic semiconductors based on CoTiSb with a very low lattice mismatch among each other are interesting materials for spintronics applications like Spin-LEDs or other spin injection devices.\nChapter 8 refers about the investigation of the theoretically predicted half-metallic completely compensated-ferrimagnet Mn$_3$Ga as a suitable material for spin torque transfer applications. The Curie temperature is above 730~K and the electronic structure calculations indicate a nearly half-metallic ferrimagnetic order with 88% spin polarization at the Fermi energy.}