Magnetic properties of p-La0.78Mn0.99O3.5 and p-La0.80Mn1.04O3.5 obtained at high pressure 7.5GPa

Structural and magnetic studies of nanocomposite samples of lanthanum manganite p-La0.78Mn0.99O3+δ and p-La0.80Mn1.04O3+δ with excess oxygen (δ=0.5) have been performed. The samples were obtained at high pressure (7.5GPa). 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 (70nm). Temperature studies of the magnetic susceptibility showed that at temperature of the order of 260K both samples pass into the ferromagnetic state. Above TC the samples exhibited paramagnetic behavior and follow the Curie–Weiss law χ=C∕(T−θ) with a positive Curie–Weiss constant θ≈280±1K for both samples. Below TC the nanocomposites exhibited spin-glass behavior. However, the field dependences of the magnetization of the samples differed substantially. The saturation fields for p-La0.78Mn0.99O3.5 and p-La0.80Mn1.04O3.5 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-La0.78Mn0.99O3.5 and p-La0.80Mn1.04O3.5 are 0.84μB and 3.24μB.