Magnetic structure and giant magnetoresistance of ferromagnetic La1-delta Mn1-delta O3 - An example of double-exchange striction?

A neutron powder diffraction study of the structure of the rhombohedral phase of La1-deltaMn1-deltaO3 (delta = 0.04) as a function of temperature has been carried out, The crystal structure is well described at all temperatures by a model in R - 3c (a = 5.52264(5) and c = 13.3309(5) at 300 K) and the low temperature data contain magnetic contributions to the Bragg scattering due to ferromagnetic ordering below T-c similar to 200 K. The spin is canted at approximately 45 degrees from [001]. The Mn-O-Mn angle decreases on cooling to T-c, but shows a slight increase on further cooling, presumably due to the onset of a double-exchange striction effect. Resistivity and magnetization data corroborate the neutron findings and reveal an insulator to metal transition close to T-c with a negative giant magnetoresistance value of similar to 50% at this temperature. The results confirm the striking similarity between the structural, magnetic, and conducting properties of rhombohedral La1-deltaMn1-deltaO3 and those of the solid solution La(1-x)A(x)MnO(3) (x similar to 0.3). (C) 1996 Academic Press, Inc.