Abstract.Heusler compounds exhibit a wide range of different electronic ground states and are hence expected to be applicable as functional materials in novel electronic and spintronic devices. Since the growth of large and defect-free Heusler crystals is still challenging, single crystals of Fe 2 TiSn and Cu 2 MnAl were grown by the optical floating zone technique. Two positron annihilation techniques -Angular Correlation of Annihilation Radiation (ACAR) and Doppler Broadening Spectroscopy (DBS) -were applied in order to study both, the electronic structure and lattice defects. Recently, we succeeded to observe clearly the anisotropy of the Fermi surface of Cu 2 MnAl, whereas the spectra of Fe 2 TiSn were disturbed by foreign phases. In order to estimate the defect concentration in different samples of Heusler compounds the positron diffusion length was determined by DBS using a monoenergetic positron beam.
IntroductionHeusler crystals comprise a large class of ternary intermetallic compounds with the L2 1 structure type and with the formula X 2 YZ where X, Y are transition metals, and Z is a non-magnetic or a nonmetallic element. The family of Heusler compounds exhibits an extraordinary wide range of different electronic ground states with metallic, semiconducting, insulating, half-metallic, ferromagnetic or superconducting behavior [1]. For novel electronic and spintronic applications great efforts are undertaken to benefit from the electronic properties of this class of materials. For this reason, it is a major task to develop new functional materials based on Heusler compounds. In order to enable the investigation of basic properties such as the electronic structure the availability of Heusler singlecrystals is of major importance. However, the growth of large and defect-free single-crystals of this class of ternary alloys remains still challenging.Within this contribution, we focus on the ternary systems Cu 2 MnAl and Fe 2 TiSn. Cu 2 MnAl is the Heusler system per se: In 1903, Fritz Heusler discovered that this compound behaves like a magnet, although none of its constituent elements is ferromagnetic by itself [2]. The Curie temperature of Cu 2 MnAl is found to be T C = 622 K. For Fe 2 TiSn various properties are theoretically predicted such as a non-magnetic ground state, a pseudogap and a very low density of states at the Fermi level [3,4].