Rongdi Guo

Relationship between Curie temperature and Brillouin function characteristics of NiCuZn ferrites

Based on Neels two-sublattice collinear model, the relationship between Curie temperature Tc and temperature characteristics of Brillouin function for NiCuZn ferrites has been studied by nonlinear fitting calculation method. According to the tetrahedral A sites and the octahedral B sites of spinel structure model which do not only contain Fe3+ but also some other multiple magnetic ions (Ni2+and Cu2+), molecular-field coefficients ωaa, ωbb, and ωab = ωba have been calculated; furthermore, the ferrimagnetism and paramagnetism Curie temperature Tc calculation formula has been modified, respectively. The magnetic moment versus temperature T (below the Curie temperature Tc) and the reciprocal of paramagnetism magnetic susceptibility 1/χm versus temperature T (beyond the Curie temperature Tc) have been investigated, respectively. The values of the calculated ferrimagnetism Curie temperature are very close to the values of the testing Curie temperature, and with the same zinc content t, the values of paramagnet...

Brillouin function characteristics for La-Co substituted barium hexaferrites

La-Co substituted barium hexaferrites with the chemical formula of Ba1−xLaxFe12−xCoxO19 (x = 0.0, 0.1, 0.3, and 0.5), prepared by a conventional ceramic method, were systematically investigated by Raman spectra, X-ray photoelectron spectroscopy, Rietveld refinement of X-ray diffraction patterns, and vibrating sample magnetometer. The result manifests that all the compounds are crystallized in magnetoplumbite hexagonal structure. Trivalent cobalt ions prevailingly occupy the 2a, 4f1, and 12k sites. According to Neel model of collinear-spin ferrimagnetism, the molecular-field coefficients ωbf2, ωkf1, ωaf1, ωkf2, and ωbk of La-Co substituted barium hexaferrites have been calculated using the nonlinear fitting method, and the magnetic moment of five sublattices (2a, 2b, 4f1, 4f2, and 12k) versus temperature T has been also investigated. The fitting results are coincided well with the experimental data. Moreover, with the increase of La-Co substitution amount x, the molecular-field coefficients ωbf2 and ωaf1 d...

Structural, magnetic and electrical properties in Al-substitued NiZnCo ferrite prepared via the sol–gel auto-combustion method for LTCC technology

Al-substituted NiZnCo ferrite, Ni0.4Zn0.5Co0.1AlxFe2−xO4 (0 ≤ x ≤ 0.20), were synthesized by the sol–gel auto-combustion method. The effects of Al substitution on the structural, magnetic and electrical properties have been investigated. The X-ray diffraction patterns show that the lattice parameter decreases with the increase of Al substitution. The SEM images show that the grain size decreases with the increase of Al substitution. The initial magnetic permeability reaches the maximum value when Al substitution is 0.05. The resonance frequency is inversely proportional to initial magnetic permeability which obeys Snoeks law. The temperature coefficient reaches the maximum value when Al substitution is 0.05, and it has the minimum value when Al substitution is 0.20. The Curie temperature decreases with the increase of Al temperature due to the number of nonmagnetic Al3+ ions increase results in the decrease of superexchange interaction. The saturation magnetization and coercivity of the ferrite decrease linearly with the increase of Al substitution. The real dielectric constant of Ni0.4Zn0.5Co0.1AlxFe2−xO4 ferrite decreases exponentially as frequency increases, and the dielectric constants decrease with the increase of Al substitution. The direct-current resistivity decreases and follows an exponential decay with the increase of temperature, and it increases with Al substitution.

Ferromagnetic Resonance Study on Si/NiO/NiFe Films

Motivated by the wide application of the antiferromagnetic/ferromagnetic (FM) bilayer structures in high-frequency microwave magnetic devices, the Si/NiO/Ni81Fe19 films with different orientations of NiO buffer layer are deposited by magnetron sputtering technology. The phase, microstructure, hysteresis loop, and angular dependence of FM resonance (FMR) linewidth are investigated by X-ray diffractometer, field-emission scanning electron microscope, atomic force microscope, vibrating sample magnetometer, and electron spin resonance spectrometer, respectively. The Si/NiO(220) film has much smaller grain size than that of Si/NiO(200) film, which is beneficial to grow a high quality NiFe film on Si/NiO(220)/NiFe bilayer structures. The hysteresis loop of Si/NiO(220)/NiFe films shows an obvious exchange bias and a relatively smaller coercivity. The FMR linewidth (ΔH) of Si/NiO(220)/NiFe films is much smaller than that of Si/NiO(200)/NiFe films, which is caused by the different structural properties and morphologies of the NiO buffer layer. The Landé g factors and effective damping parameters αeff are also discussed.

Effects of BaM Interfacial Layer on the

M-type barium ferrite (BaM) thin films with two different structures (single layered and double layered) were deposited on thermally oxidized silicon (SiO2/Si) substrates by radio frequency (RF) magnetron sputtering. The changes in surface morphologies, crystallographic and magnetic properties of the films corresponding to different structures and substrate temperatures (Ts) were investigated in detail. In the single layered films deposited directly on SiO2/Si substrates at Ts = 300°C and Ts = 500°C respectively, most of the grains are acicular type. XRD data and magnetic properties measurement confirmed that they are both weakly c-axis perpendicularly oriented. However, in the double layered film with first interfacial layer deposited at Ts = 300°C and second layer deposited at Ts = 500°C, good crystallographic characteristics and excellent perpendicular c-axis orientation were obtained. The c-axis dispersion angle (Δθc) decreased to 0.51°C; the lattice parameters were comparable to those of the bulk BaM; the squareness ratio and coercivity of the out-of-plane increased to 0.85 and 338 kA/m, respectively, for the double layered film. The mechanism for improving perpendicular -axis orientation with an interfacial BaM layer was attributed to two reasons. One is a relative increase in the nucleation sites for perpendicularly oriented grains over the nucleation sites for in-plane and/or randomly oriented grains, and the other is the release of stress that comes from the interface between BaM thin film and SiO2/Si substrate.

c

The effects of Bi2O3 on dispersion spectra of permeability and permittivity for LiZnMn ferrite prepared by a conventional ceramic method were investigated. Optimum content of Bi2O3 can obviously affect the permeability and permittivity of LiZnMn ferrite via promoting grain growth and densification. The permeability spectra of LiZnMn ferrite were resolved into two contribution components, domain wall movement and spin rotation magnetization. The fitting results manifest that, with Bi2O3 concentration increasing, the major contribution to dynamic magnetization changes from spin rotation magnetization mechanism to domain wall movement, and the domain wall spectra change from resonance-type to relaxation-type, but the spin rotation spectra behave in the opposite way. Meanwhile, the mechanism of dielectric polarization and dielectric loss of the samples were discussed.

-Axis Orientation of BaM Thin Films Deposited on SiO

In this work, one carried out the Rietveld refinement to exactly identify the cation distribution of Ni-substituted MnZn ferrites. Then, one investigated the temperature dependence of Brillouin function based on the experimental and fitting molecule magnetic moment under the Neel model of collinear-spin ferrimagnetism.

_{2}

Barium hexaferrites BaFe₁₂O₁₉ with Bi₂O₃/CuO additives are synthesized in this study by conventional oxide ceramic process and characterized using SEM. Saturation magnetization and remanence properties are determined as the amount of additives is varied. It is shown that the additives segregate in the grain boundary regions, and significantly promote grain growth and sintering densification.

/Si Substrates

Ni-substituted manganese-zinc (MnZn) ferrites with the composition of Mn_0.506-xZn_0.244Ni_xFe_2.250O_4.0 (x = 0.066~0.122) have been prepared by the solid-state reaction method. The cation distribution has been investigated by the Rietveld refinement of X-ray diffraction patterns, the microstructure has been observed using a scanning electron microscope, and the magnetic property has been measured using superconductor quantum interference devices and B-H analyzer. The results show that Zn²⁺ and Ni²⁺ ions prefer to occupy the tetrahedron site (A sublattice) and octahedron site (B sublattice), respectively. However, Mn²⁺ and Fe³⁺ ions can enter into A and B sublattices, where the ratio of Mn²⁺ ions occupying A and B sublattices is 4:1. The lattice parameter (a) of the samples decreases with the increase of Ni-substituted content. Meanwhile, based on the Neel model of collinear-spin ferrimagnetism, the molecular-field coefficients ω_AA, ω_BB, and ω_AB of the Ni-substituted MnZn ferrites have been calculated, and the magnetic moment of A and B sublattices versus temperature T has also been investigated. The fitting results match well with the experimental data. Both ω_AB and ω_BB increase with the increase of the Ni-substituted content, but ω_AA shows the opposite variation trend. The Curie temperature also increases with the increasing of the Ni-substituted content, which is attributed to the enhancement of superexchange interaction for A-B sublattice. In addition, the temperature dependence of initial permeability and core loss has been discussed.

Dispersion Spectra of Permeability and Permittivity for LiZnMn Ferrite Doped With

Barium hexaferrites BaFe₁₂O₁₉ with Bi₂O₃/CuO additives were synthesized by the conventional oxide ceramic process. The results manifest that Bi₂O₃ additives mainly concentrate on the grain boundary regions, while CuO additives could both enter into the grain and segregate at the grain boundary regions. The appropriate sintering temperature of barium hexaferrites with Bi₂O₃ and Bi₂O₃+ CuO additives reaches 1020 °C and 920 °C, respectively. As the amount of Bi₂O₃ is 3 wt%, the specimens of BaFe₁₂O₁₉ show saturation magnetization (Ms) of 346 kA/m, remanence (Mr) of 227 kA/m, and density (d) of 5.06 g/cm³. Meanwhile, the combination of 3 wt% Bi₂O₃ and 3 wt% CuO additives significantly promotes grain growth and sintering densification, with a high saturation magnetization of 371 kA/m and density of 5.23 g/cm³ for BaFe₁₂O₁₉, which are pretty close to the theoretical values (380 kA/m, 5.28 g/cm³). Moreover, the corresponding remanence could also rise by 10% compared with that in the sintered samples with 3 wt% Bi₂O₃.