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

The magnetic and magnetotransport properties of La0.7Sr0.3Mn1-xNixO3 (x les s than or equal to 0.4) system have been studied. It is found that Ni dopin g induces a ferromagnetic state to ferromagnetic cluster state transition n ear 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 sam ple shows both a rapid low-field MR and a slow high-field MR increase and a bove which only a slow MR increase is observed. The results suggest that th e 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 m oments associated with the magnetically disordered regions inside grains wh ich may serve as the spin-dependent scattering centers as well as the pinni ng centers for magnetic domain walls.