Unusual transport properties of ferromagnetic Heusler alloy Co$_2$TiSn
  We report results of magnetization, zero field resistivity and magnetoresistance measurements in ferromagnetic Heusler alloy Co$_2$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 and this changes abruptly to metallic behaviour at the onset of ferromagnetic ordering. Application of external magnetic field tends to suppress this semiconducting like transport leading to a negative magnetoresistance which reaches a peak in the vicinity of Curie temperature. Comparison is made with the similar unusual behaviour observed in other systems including UNiSn and manganites. 
S. Majumdar, M. K. Chattopadhyay, V. K. Sharma, K. J. S. Sokhey, S. B.   Roy and P. Chaddah