Phase coexistence and magnetic anisotropy in polycrystalline and nanocrystalline LaMnO3+δ

We report on the phase coexistence and magnetic anisotropy in polycrystalline (bulk) and nanocrystalline (∼15 nm) LaMnO3+δ materials, which were prepared by solid state reaction and sol-gel methods, respectively. In addition to standard magnetization measurements, radio-frequency transverse susceptibility (TS) based on a very sensitive, self-resonant tunnel diode oscillator method was used to probe magnetic anisotropy and switching fields in the samples. The results revealed a coexistence of the ferromagnetic (FM) and antiferromagnetic (AFM) phases in both samples. For the bulk sample, the AFM phase significantly changed in volume fraction at ∼30 K and completely vanished around 120 K. Size reduction to the nanometer scale (∼15 nm) significantly suppressed the AFM phase while inducing surface spin disorder in the material. The large magnetic anisotropies were probed by TS experiments in both samples. Our studies showed that the magnetic properties of bulk LaMnO3+δ were strongly modified by size reduction.