Double metal?insulator transitions and MR in La0.67Ca0.33Mn1$minus;xRuxO3 (x$les;0.10): a qualitative understanding in light of possible magnetic phase separation

Abstract

We report results of the magnetotransport measurements on La 0.67 Ca 0.33 Mn 1− x Ru x O 3 (0⩽ x ⩽0.1) compounds in the light of proposed magnetic phase separation in our previous work wherein two metal to insulator transitions (MITs) were reported (J. Magn. Magn. Mater. 257 (2003) 195). With the application of magnetic field, a significant reduction in resistance and a shift in MITs to higher temperatures but with different rates are observed. The temperature dependent magnetoresistance (MR) exhibits two maxima, a pronounced one at higher temperature and a shallow one at low temperature, corresponding to the two MITs. The peak value of MR at high temperature MITs ( H =5 T) does not change systematically with Ru concentration. The low temperature MR peak becomes perceptible for x ⩾0.03 and shows a nominal enhancement with Ru concentration. The double maxima, both exhibiting MR phenomena in the magnetotransport properties of Ru-doped manganites are analysed within the context of magnetic phase separation.