Growth and magnetic properties of single crystal Co2MnX (X = Si, Ge) Heusler alloys

Half-metallic (HM) ferromagnetic materials have recently drawn intense inte rests due to their potential use in magnetoelectronic devices. Co-based Heu sler alloys of the type Co2MnX (X = Si, Ge), predicted to be EM by first pr inciples band structure calculations, are of particular interest since they alone possess Curie temperatures in excess of 900 K. Since the spin polari zation (P) is believed to be sensitive to antisite defects that are likely to occur in vapor-quenched thin film synthesis, single crystals of Co-2 MnX (X = Si, Ge) were prepared using the tri-arc Czochralski method. X-ray dif fraction, including Laue backscattering, was employed to determine the high crystalline quality of these crystals. SQUID magnetometry measured a magne tic moment per formular unit that is close to the calculated value indicati ng that these alloys may in fact be EM. However, point contact Andreev refl ection, a technique that has reliably measured high P in CrO2, measures P v alues for these crystals of 50-60%, well below their theoretical values. Th e reduced spin polarization may be due to the effects of crystal symmetry b reaking at the surface or the presence of antisite defects, or that these m aterials are not truly half-metallic.