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要旨:
In this work, the theoretical and experimental investigations of
Co(2)TiZ (Z = Si, Ge or Sn) compounds are reported. Half-metallic
ferromagnetism is predicted for all three compounds with only two bands
crossing the Fermi energy in the majority channel. The magnetic moments
fulfil the Slater-Pauling rule and the Curie temperatures are well above
room temperature. All compounds show a metallic-like resistivity for low
temperatures up to their Curie temperature, above the resistivity
changes to semiconducting-like behaviour. A large negative
magnetoresistance (MR) of 55 per cent is observed for Co2TiSn at room
temperature in an applied magnetic field of mu H-0 = 4T, which is
comparable to the large negative MRs of the manganites. The Seebeck
coefficients are negative for all three compounds and reach their
maximum values at their respective Curie temperatures and stay almost
constant up to 950 K. The highest value achieved is -52 mu VK-1 for
Co2TiSn, which is large for a metal. The combination of half-metallicity
and the constant large Seebeck coefficient over a wide temperature range
makes these compounds interesting materials for thermoelectric
applications and further spincaloric investigations.
