Magnetic Structure and Giant Magnetoresistance of Ferromagnetic La1−δMn1−δO3—An Example of Double-Exchange Striction?

Abstract

A neutron powder diffraction study of the structure of the rhombohedral phase of La1−δMn1−δO3(δ = 0.04) as a function of temperature has been carried out. The crystal structure is well described at all temperatures by a model inR− 3c(a= 5.52264(5) andc= 13.3309(5) at 300 K) and the low temperature data contain magnetic contributions to the Bragg scattering due to ferromagnetic ordering below Tc∼ 200 K. The spin is canted at approximately 45° from [001]. The Mn–O–Mn angle decreases on cooling toTc, 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 toTcwith a negative giant magnetoresistance value of ∼50% at this temperature. The results confirm the striking similarity between the structural, magnetic, and conducting properties of rhombohedral La1−δMn1−δO3and those of the solid solution La1−xAxMnO3(x∼ 0.3).