Crystal Structure, Magnetism, and Dielectric Properties of La_<1-x>Bi_xNi_<0.5>Mn_<0.5>O_3(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We have synthesized the polycrystalline La_<1-x>Bi_xNi_<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 P2_1/c structure with centrosymmetry for 0≤x≤0.7, and has a monoclinic C2 structure with non-centrosymmetry for 0.8≤x≤0.9 at room temperature. The ferromagnetic Curie temperature (T_CM) decreases monotonically from 300K at x=0 to 150K 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 150K, which is close to T_CM. However, no evidence showing a ferroelectric ordering was observed below 400K. For x=0.7, the increment of the dielectric constant induced by the magnetic field is 7% at T_CM at 9T. 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.
社団法人日本物理学会の論文
2008-08-15