Magnetic properties of p-La{sub}0.78Mn{sub}0.99O{sub}3.5 and p-La{sub}0.80Mn{sub}1.04O{sub}3.5 obtained at high pressure 7.5 GPa

摘要

Structural and magnetic studies of nanocomposite samples of lanthanum manganite p-La{sub}0.78Mn{sub}0.99O{sub}(3+δ) and p-La{sub}0.80Mn{sub}1.04O{sub}(3+δ) with excess oxygen (δ-0.5) have been performed. The samples were obtained at high pressure (7.5 GPa). X-Ray studies showed that the samples consist of a single phase and possess perovskite cubic structure. The lattice parameters were determined. Scanning atomic-force microscopy was used to find the characteristic sizes of the nanograins (70 nm). Temperature studies of the magnetic susceptibility showed that at temperature of the order of 260 K both samples pass into the ferromagnetic state. Above T{sub}c the samples exhibited paramagnetic behavior and follow the Curie-Weiss law x=C/(T-θ) with a positive Curie-Weiss constant θ≈280± 1 K for both samples. Below T{sub}c the nanocomposites exhibited spin-glass behavior. However, the field dependences of the magnetization of the samples differed substantially. The saturation fields for p-La{sub}0.78Mn{sub}0.99O{sub}3.5 differed by a factor of 4, and a strong temperature dependence of the magnetic rigidity was observed for both compounds. The effective magnetic moments for p-La{sub}0.78Mn{sub}0.99O{sub}3.5 and p-{sub}0.80Mn{sub}1.04O{sub}3.5 are 0.84μ{sub}B and 3.24μ{sub}B.