Magnetic glass behavior and magnetoresistive properties of perovskite cobaltites La0.7Sr0.3Co1-yGayO3

The magnetic, transport, and magnetoresistive properties of the novel perov skites La0.7Sr0.3(Co1-yGay)O-3 have been investigated. With Ga substitution , the magnetic glass state develops with competing ferromagnetic component and antiferromagnetic component in y = 0.1, and prevalent antiferromagnetic component in y = 0.2. Furthermore, Ga substitution leads to the insulating behavior from 1.5 K to 300 K and significantly enhances the magnetoresista nce particularly for La0.7Sr0.3Co0.8Ga0.2O3 at low temperatures. The replac ement of Co by Ga diluting the ferromagnetism and separating the metallic " hole rich" region to smaller clusters isolated in the ''hole poor'' matrix where thermally induced spin-state transition could occur, are suggested to explain the experimental results. Besides, some different and common featu res of magnetotransport between perovskite manganites and present cobaltite s are pointed but. [S0163-1829(99)00545-7].