Atomic order and transferred hyperfine field in CO2TiSn reexamined by tin-119 Mossbauer spectroscopy

The tin-119 Mossbauer spectra of Co2TiSn have been measured between 83 and 390 K. In Co2TiSn, which belongs to the L2(1) type of Heusler alloys, each of the constituent atoms occupies a single cubic crystallographic site. Below the Curie temperature of 371 K, the tin atoms experience a sizeable transferred hyperfine field that increases from 48.0 T at 350 K to 79.5 T at 83 K. At 350 K, the spectrum reveals the presence of both ferromagnetic and paramagnetic regions in Co2TiSn. Their coexistence may result from some titanium-tin site exchange, an exchange that leads to a distribution of tin and titanium in the second near neighbors of the tin atoms and accounts for the large observed spectral line widths. At 390 K, above the Curie temperature, the singlet paramagnetic tin-119 Mossbauer spectrum is also substantially broadened, a broadening, which may result from a distribution of isomer shift and quadrupole splittings due to the distribution of tin and titanium in the second near neighbors of the tin atoms. (C) 2004 Elsevier B.V. All rights reserved.