Magnetic, electrical properties and magnetoresistance of Cu substituted La0.7Sr0.3CoO3-delta crystals (0.35 <=delta <= 0.45)

The magnetic susceptibility, resistivity, and magnetoresistance of La0.7Sr0 .3Co1-xCux O (0 less than or equal to x less than or equal to 0.4 and 0.3 l ess than or equal to delta less than or equal to 0.4) compounds have been s tudied for applied field up to 50 kOe. Cuire temperature and saturation mag netization of the ferromagnetic perovskite La0.7Sr0.3Co1-xCuxO decreases, w hen cobalt is substituted by copper. In the doping, all coballtites exhibit ed ferromagnetic long-range ordered behaviors. If the content of copper exc eeds 10%, the electronic properties of the material show the behavior of tr ansformation from metallic to semiconductor. The semiconducting behavior is connected with the magnetic disorder, which show variable range hopping, l og rho similar to T-1/4. The magnetoresistance, which can be expressed as M R proportional to H-q when H less than or equal to 10 kOe, is negative and exceeds 32%. The results are interpreted in terms of a double-exchange and super-exchange model. (C) 1999 Elsevier Science S.A. All rights reserved.