Transport properties of the ferromagnetic Heusler alloy Co 2 TiSn

We report the results of magnetization, zero-field resistivity, and magnetoresistance measurements in the ferromagnetic Heusler alloy ${\mathrm{Co}}_{2}\mathrm{TiSn}$. There is a striking change in the character of electron transport as the system undergoes the paramagnetic to ferromagnetic transition. In the paramagnetic state, the nature of the electron transport is like that of a semiconductor. This changes abruptly to metallic behavior at the onset of ferromagnetic ordering. Application of external magnetic field tends to suppress this semiconducting-like transport leading to a negative magnetoresistance that reaches a peak in the vicinity of the Curie temperature. Comparison is made with the similar unusual behavior observed in other systems, including UNiSn and manganites.