Search

The structures, magnetic properties, permittivity spectra, and magnetodielectric (MD) effects of polycrystalline Y3Fe5-xSnxO12 compounds prepared by solid state reactions were systematically investigated. The substitution of Sn4+ leads to lattice expansion and the donation of excess electrons in ceramics, which affects the concentration of Fe2+, space charge, and electric dipole. As a result, as the amount of Sn dopant increases, so does saturation magnetization and permittivity in the low frequency band. The MD coefficient ([εr(H)?-?εr(0)]/εr(0)) of lightly doped samples (x?≤?0.05) is negative in the entire frequency band, reaching -2.3% at 350?MHz and 0.6 T for Y3Fe4.95Sn0.05O12 ceramics. The MD coefficient of heavily doped samples (x?>?0.05) is positive in the low frequency band, reaching 0.83% at 10?MHz and 0.6 T for Y3Fe4.925Sn0.075O12 ceramics, and then decreasing with the increasing frequency, gradually becoming negative in the high frequency band. A detailed explanation is provided based on the origin of permittivity. This study provides a new methodology according to which the MD materials may be designed in order to satisfy the requirements of engineering applications. [ABSTRACT FROM AUTHOR]

Fe-6.5%Si alloy powders coated with manganese oxides using an innovative in situ process were investigated. The in-situ coating of the insulating oxides was realized with a KMnO4 solution by a chemical process. The insulating manganese oxides with mixed valance state were verified by X-ray photoelectron spectroscopy analysis. The thickness of the insulating layer on alloy particles was determined to be in a range of 20-210 nm, depending upon the KMnO4 concentration. The powder core loss and the change in permeability under a DC-bias field were measured at frequencies ranging from 50 to 100 kHz. The experiments indicated that the Fe-6.5%Si powder cores with a 210 nm-thick manganese oxide layer not only showed a low core loss of 459 mW/cm3 at 100 kHz but also showed a small reduction in permeability (μ(H)/μ(0) = 85% for μ = 42) at a DC-bias field of 80 Oe. This work has defined a novel pathway to realizing low core loss and field-insensitive permeability for Fe-Si powder cores. [ABSTRACT FROM AUTHOR]