Abstract
We report a series of magnetic and magnetotransport studies performed on Ga-substituted manganite compounds We replace half of the Mn ions in with diamagnetic ions and find that the system transforms into a ferromagnet as the result of local coherent and incoherent distortions. Following additional doping with Sr ions we find that the compounds remain ferromagnetic up to but for higher concentrations the competition between the ferromagnetic and antiferromagnetic superexchange interactions, together with the randomness in distribution of the magnetic ions, lead to magnetic frustration, cluster-glass and spin-glass behavior. All compounds are insulating and the activation energy decreases almost linearly with x. measurements suggest the existence of short-range magnetic correlations in the high-temperature region. We measure a significant increase in the muon-spin relaxation rate at low temperatures due to fluctuations of random internal magnetic fields. The observed magnetoresistance in the high-temperature region is mainly a consequence of the reduction of the spin disorder on a local scale, and is as high as 50% in 14 T and for samples with and
- Received 11 July 2001
DOI:https://doi.org/10.1103/PhysRevB.65.054402
©2001 American Physical Society