Magnetic and magnetotransport properties in the Ni-doped La0.7Sr0.3MnO3 system

The magnetic and magnetotransport properties of La0.7Sr0.3Mn1-xNixO3 (x less than or equal to 0.4) system have been studied. It is found that Ni doping induces a ferromagnetic state to ferromagnetic cluster state transition near the metallic critical threshold composition. Interestingly, the largest low-temperature magnetoresistance (MR) at 77 K is found in the samples in the vicinity of the ferromagnetic threshold composition-below which the sample shows both a rapid low-field MR and a slow high-field MR increase and above which only a slow MR increase is observed. The results suggest that the spin-dependent scattering from internal grain regions is also responsible for the low-temperature MR. The low-temperature and low-field Me effect is explained in terms of orientation of the magnetic domains or/and cluster moments associated with the magnetically disordered regions inside grains which may serve as the spin-dependent scattering centers as well as the pinning centers for magnetic domain walls.