Effect of Cr and Fe doping on the transport and magnetic properties of the low-bandwidth bilayered manganite Sm_1.4Sr_1.6Mn₂O₇

The resistivity under different magnetic fields and the magnetization of Cr- and Fe-doped Sm_1.4Sr_1.6Mn₂O₇ have been measured. Fe and Cr doping affect differently. With increase of Cr content the metal-insulator (M-I) transition temperature (T_MI) is shifted to lower temperature, whereas even with 1% Fe doping M-I transition disappears and reappears with the application of 2 T magnetic field. This may be due to the fact that Fe doping induces magnetic disorder which strongly localizes the charge carriers. The most of the presently studied samples exhibit huge magnetoresistance (MR) and the maximum MR of 99.49% in 4 T magnetic field has been observed for 1% Cr-doped sample. Besides the fact that the ground state of all the samples is antiferromagnetic the magnetization data indicate the existence of ferromagnetic clusters except the 5% Fe doped sample which shows spin-glass-like behavior.