Crystal Structure, Magnetism, and Dielectric Properties of La1-xBixNi0.5Mn0.5O₃

We have synthesized the polycrystalline La 1- x Bi x Ni 0.5 Mn 0.5 O 3 for x =0–0.9 by soft chemical synthesis, and investigated the crystal structure, and the magnetic and the dielectric properties. The crystal has a monoclinic P 2 1 / c structure with centrosymmetry for 0≤ x ≤0.7, and has a monoclinic C 2 structure with non-centrosymmetry for 0.8≤ x ≤0.9 at room temperature. The ferromagnetic Curie temperature ( T CM ) decreases monotonically from 300 K at x =0 to 150 K at x =0.9, while the Ni 2+ –Mn 4+ configuration is kept independent of Bi-content. For x ≥0.5, An anomalous increment of the dielectric constant with increasing temperature and the maximum in the dielectric loss accompanied with frequency dispersion were observed around 150 K, which is close to T CM . However, no evidence showing a ferroelectric ordering was observed below 400 K. For x =0.7, the increment of the dielectric constant induced by the magnetic field is 7% at T CM at 9 T. The temperature and the magnetic field dependence of the dielectric properties is discussed based on Maxwell–Wagner model assuming an inhomogeneity of samples and a negative magnetoresistance.