Solution combustion synthesis method and magnetic properties of synthesized polycrystalline calcium manganite CaMnO3-delta powder
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We present a modified solution combustion synthesis method and measured magnetic properties of CaMnO3-delta (calcium manganite). The structure, morphology and magnetic properties of CaMnO3-delta were investigated by XRPD (X-ray powder diffraction), TEM (transmission electron microscopy), HRTEM (high-resolution transmission electron microscopy) and SQUID (superconducting quantum interference device). The XRPD study revealed that the prepared sample is composed of pure calcium manganite phase. The TEM and HRTEM images showed well-crystallized particles with a rough surface and particle size of about 100 nm. Magnetization measurements revealed magnetic transition at T-N=120 K, which corresponds to the Neel temperature of calcium manganite. Paramagnetic behavior was measured above the TN temperature. High irreversibility between the ZFC (zero-field cooled) and the FC (field cooled) curves below TN were observed. In addition, the separation between ZFC and FC curves increased with increasin...g magnetic field. We also show that the temperature values at the maxima of the ZFC curves are insensitive to the value of the applied DC magnetic field and to the frequency of the AC magnetic field. Magnetic measurements also indicate the presence of a strong antiferromagnetic exchange coupling with a Curie-Weiss temperature theta=-436 K. Magnetic moment of 4.33 mu(B) per Mn ion is determined from the Curie constant. This value of the magnetic moment suggests that Mn3+ and Mn4+ ions exist in the sample. Measurements of the magnetic hysteresis properties indicate a contribution of a ferromagnetic-like component in the sample. This is revealed by large coercivity and high remanence magnetization below TN. In this work we also studied field-cooled (up to 5 T) hysteresis properties of the sample. The detailed analysis of these results suggests a minor hysteresis loop behavior and no exchange bias.