Electron doping in the half-metallic ferromagnet CrO2 oxide has been reache
d via partial Cr substitution by Mn. Synthesis of ceramic samples is accomp
lished under high temperature and high oxygen pressure. It is found that el
ectron doping reduces the magnetization and the Curie temperature of the sa
mples. Simultaneously, the low temperature and low field magnetoresistance
of the samples increase. The results are discussed on the light of the curr
ent models for the electronic structure of this oxide and the possible role
of segregated insulating impurity phases. (C) 2000 American Institute of P
hysics. [S0021-8979(00)79308-X].