Magnetic, electrical properties and magnetoresistance of Cu substituted La0.7Sr0.3CoO3−δ crystals (0.35≤δ≤0.45)

The magnetic susceptibility, resistivity, and magnetoresistance of La0.7Sr0.3Co1−xCux O (0≤x≤0.4 and 0.3≤δ≤0.4) compounds have been studied for applied field up to 50 kOe. Cuire temperature and saturation magnetization of the ferromagnetic perovskite La0.7Sr0..3Co1−xCuxO decreases, when cobalt is substituted by copper. In the doping, all coballtites exhibited ferromagnetic long-range ordered behaviors. If the content of copper exceeds 10%, the electronic properties of the material show the behavior of transformation from metallic to semiconductor. The semiconducting behavior is connected with the magnetic disorder, which show variable range hopping, log ρ∼T−1/4. The magnetoresistance, which can be expressed as MR∝Hq when H≤10 kOe, is negative and exceeds 32%. The results are interpreted in terms of a double-exchange and super-exchange model.