In the present work, the structure, magnetic, and dielectric characteristics of Nd2NiMnO6 and Sm2NiMnO6 have been investigated with comparison to those for La2NiMnO6. The magnetic and dielectric properties of the present ceramics vary with decreasing lanthanide ionic radius (RLn). Both Nd2NiMnO6 and Sm2NiMnO6 are ferromagnetism with the monoclinic symmetry (space group P21/n). The Curie temperature TC of Nd2NiMnO6 and Sm2NiMnO6 is 194 K and 156 K, respectively, and it decreases with decreasing 〈Ni-O-Mn〉 bond angle which depends on RLn. Meanwhile, the dielectric constant ε′ monotonically decreases with decreasing RLn. The similar variation tendency of magnetic and dielectric characteristics with RLn indicates that the structural origins for the magnetic and dielectric response should be closely linked with each other.
Laminated magnetoelectric (ME) composites are suitable for applications such as magnetic field sensors, transformers, and microwave resonators. Such applications frequently involve environments where the temperature alters. The present work investigates the temperature dependent ME coupling for three kinds of laminates, namely, Terfenol-D/PZT/Terfenol-D, Ni/PZT/Ni, and Metglas/PZT/Metglas. The Terfenol-D/PZT/Terfenol-D is shown to exhibit the best temperature stability. The peak value of the ME coefficient versus temperature curve is predicted for the laminates based on the equivalent circuit model, as well as the measurements of temperature dependent magnetostriction for Terfenol-D, Ni, and Metglas. The predictions agree well with the experimental data, implying that the piezomagnetic coefficient, d11,m, of the magnetic layer plays an important role in the temperature dependent ME coupling of the laminate.
Dielectric properties of La2CuTiO6 ceramics were investigated in a broad frequency and temperature range. There is only one dielectric relaxation in the curve of temperature dependence of dielectric properties for La2CuTiO6 ceramics. This dielectric relaxation is a thermal activated process. The bulk and grain boundary resistances can be obtained from results of the least-mean-square fitting on impedance spectra. The conduction mechanism of the present ceramics is also a thermal activated process. The activation energy of dielectric relaxation is almost same as that of electrical conductivity and this indicates the closely correlation between the dielectric relaxation and electrical conductivity. The dielectric relaxation in the present ceramics should be attributed to the mixed-valent structure (Cu+/Cu2+ and Ti3+/Ti4+), which is induced from the oxygen vacancy.
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