Effect of Li substitution on the magnetic properties of LixMg0.40Ni0.60−2xFe2+xO4 ferrites

Structural and magnetic properties of a series of polycrystalline spinel type ferrites with the nominal chemical composition Li_xMg_0.40Ni_0.60−2xFe_2+xO₄, where x=0.0-0.3 in steps of 0.05, were investigated thoroughly. The formation of spinel structure was confirmed by X-ray diffraction analysis. Lattice constants and average grain diameters increased with increase in Li content. The real part of the initial permeability (μ^/_i) is found to increase not only with increase in Li content up to x=0.25 but also with the increase in sintering temperature up to 1100 °C. However, it decreases for further increase in sintering temperature except for x=0 and 0.05 compositions. The grain size dependent μ^/_i is also observed clearly in this research. From the magnetization as a function of applied magnetic field plots, it is clear that all samples exhibit ferrimagnetic state at room temperature and have a low saturation field. The magnetization obtained is explained with the help of redistribution of cations in the tetrahedral and octahedral sites and spin canting due to weakening of exchange interaction.     

Influence of the cation distribution on the magnetization of Y-type hexagonal ferrites

Mössbauer absorption and magnetization measurements have been made in Mg₂?Y and Co₂?Y ferrites. The magnetizations of the various iron sublattices did not show any marked difference in Mg₂?Y, whilst in the case of Co₂?Y three different behaviours of the sublattice magnetizations have been detected. Low-temperature magnetization measurements in Mg₂Y gave evidence of a noncollinear magnetic order. The different magnetic properties of these compounds have been explained on the ground of a preferential occupation by Mg²⁺ and Co²⁺ ions of the inner octahedral sites of the T crystallographic block. The presence in these sites of a non-magnetic ion such as Mg²⁺ is responsible for the peculiar magnetic order observed in Mg₂?Y.     

Effect of quenching temperature on magnetization and cation distribution in magnesium based UHF ferrites

The paper gives the results of measuring the specific saturation magnetization, cation distribution in the sublattices, and Curie points for alumino-magnesium, magnesium-chromium, and magnesium-manganese UHF-ferrites according to quenching temperature. General formulas were obtained for sublattice cation distribution in magnesium-based mixed ferrite-spinels, and the results of theoretical analysis were compared with experimental findings.     

Temperature dependence of core loss in cobalt substituted Ni-Zn-Cu ferrites

The temperature dependence of core loss in cobalt substituted Ni-Zn-Cu ferrites was investigated. Co²⁺ ions are known to lead to a compensation of the magneto-crystalline anisotropy in Ni-Zn ferrites, at a temperature depending on the cobalt content and the Ni/Zn ratio. We observed similar behaviour in Ni-Zn-Cu and it was found that the core loss goes through a minimum around this magneto-crystalline anisotropy compensation. Moreover, the anisotropy induced by the cobalt allowed a strong decrease of core loss, a ferrite having a core loss of 350 mW/cm³ at 80 °C was then developed (measured at 1.5 MHz and 25 mT). This result represents an improvement of a factor 4 compared to the state of art Ni-Zn ferrites.     

Low temperature sintering of sub-stoichiometric Ni-Cu-Zn ferrites: Shrinkage, microstructure and permeability

We have studied sub-stoichiometric Ni-Cu-Zn ferrites with iron deficiency (i.e., <50mol% Fe₂O₃) of composition Ni_0.20Cu_0.20Zn_0.60+zFe_2−zO_4−(z/2) with 0≤z≤0.06. The temperature of maximum shrinkage rate is shifted from T=1000 °C for z=0 towards lower temperatures down to T=900 °C for a sub-stoichiometric ferrite with z=0.02. Dense samples are obtained after firing at 900 °C for z>0 only. Sub-stoichiometric compositions (z>0) do not form single-phase spinel ferrites after sintering at 900 °C, but rather represent mixtures of CuO and a stoichiometric ferrite with slightly modified composition. The formation of small amounts of CuO at grain boundaries is demonstrated by XRD and SEM. The permeability is increased from μ=80 for stoichiometric ferrites (z=0) to μ=660 for z=0.02. The formation of CuO during sintering of sub-stoichiometric ferrites supports densification and is a prerequisite for low temperature firing of multilayer inductors. Addition of 1 wt% Bi₂O₃ as liquid phase sintering aid is required to provide sufficient densification of the stoichiometric ferrite (z=0) at 900 °C. Addition of 0.37 wt% Bi₂O₃ to a sub-stoichiometric ferrite (z=0.02) results in dense samples after firing at 900 °C; however, the microstructure formation is dominated by heterogeneous grain growth.     

Influence of anionic substitutions on hyperfine interactions and ionic ordering in ferrites

Hyperfine Interactions -     

Effect of thermal treatment on the magnetization processes of nanocrystalline Fe80Ge3Nb10B7 alloys

The dynamic magnetization processes of nanocrystalline Fe₈₀Ge₃Nb₁₀B₇ alloys after annealing at different temperatures are studied through the permeability spectroscopy. Three steps of crystallization are found when amorphous Fe₈₀Ge₃Nb₁₀B₇ alloys are heated from 300to 1200 K. The dominant magnetization process varies with different annealing temperatures. Domain wall bulging is the main magnetization mechanism under weak applied field. When the applied field exceeds pinning field H_p, the depinning-involved domain wall displacement occurs. Different annealing temperature results in different H_p. The lower value of μ′ and high relaxation frequency after heating at 923 and 973 K are due to the strengthened domain wall pinning and the increase of magnetocrystalline anisotropy.     

Zn- and Cu-substituted Co2Y hexagonal ferrites: Sintering behavior and permeability

Y-type polycrystalline hexagonal ferrites Ba₂Co_2−x−yZn_xCu_yFe₁₂O₂₂ with 0≤x≤2 and 0≤y≤0.8 were prepared by the mixed-oxide route. Single phase Y-type ferrite powders were obtained after calcinations at 1000 °C. Samples sintered at 1200 °C show a permeability that increases with the substitution of Zn for Co and display maximum permeability of μ′=35 at 1 MHz for x=1.6 and y=0.4. A resonance frequency f_r=500 MHz is observed for Zn-rich ferrites with y=0 and 0.4. The saturation magnetization increases with substitution of Zn for Co. Addition of Bi₂O₃ shifts the temperature of maximum shrinkage down to T≤950 °C. Moreover, an increase of the Cu-concentration further lowers the sintering temperature to T≤900 °C, enabling co-firing of the ferrites with Ag metallization for multilayer technologies. However, low-temperature firing reduces the permeability to μ′=10 and the resonance frequency is shifted to 1 GHz. Thus substituted hexagonal Y-type ferrites can be used as soft magnetic materials for multilayer inductors for high frequency applications.     

Influence of the nitrogen contents on the permeability characteristics and soft magnetic properties of FeHfN films

High permeability magnetic films can enhance the inductance of thin-film inductors in DC-DC converters. In order to obtain high permeability, the uniaxial anisotropy and coercivity should be as low as possible. This study employed dc reactive magnetron sputtering to fabricate nanocrystalline FeHfN thin films. The influence of the nitrogen flow on the composition, microstructure, and permeability characteristics, as well as magnetic properties was investigated. Increasing the nitrogen content can alter FeHfN films from amorphous-like to crystalline phases. The magnetic properties and permeability depend on variations in the microstructure. With the optimum N₂/Ar flow ratio of 4.8% (N₂ flow: 1.2 sccm), low anisotropy (H_K = 18 Oe), low coercivity (H_C = 1.1 Oe) and high permeability (μ′ > 600 at 50 MHz) were obtained for fabrication of a nanocrystalline FeHfN film with a thickness of around 700 nm. Such as-fabricated FeHfN films with a permeability of over 600 should be a promising candidate for high-permeability ferromagnetic material applications.     

Influences of Bi2O3 additive on the microstructure, permeability, and power loss characteristics of Ni-Zn ferrites

Nickel-zinc ferrite materials containing different Bi₂O₃ concentrations have been prepared by the conventional ceramic technique. Micrographs have clearly revealed that the Bi₂O₃ additive promoted grain growth. When the Bi₂O₃ content reached 0.15 wt%, a dual microstructure with both small grains (<5 μm) and some extremely large grains (>50 μm) appeared. With higher Bi₂O₃ content, the samples exhibited a very large average grain size of more than 30 μm. The initial permeability gradually decreased with increasing Bi₂O₃ content. When the Bi₂O₃ content exceeded 0.15 wt%, the permeability gradually decreased with frequency due to the low-frequency resonance induced by the large grain size. Neither the sintering density nor the saturation magnetization was obviously influenced by the Bi₂O₃ content or microstructure of the samples. However, power loss (Pcv) characteristics were evidently influenced. At low flux density, the sample with 0.10 wt% Bi₂O₃, which was characterized by an average grain size of 3-4 μm and few closed pores, displayed the lowest Pcv, irrespective of frequency. When the flux density was equal to or greater than the critical value of 40 mT, the sample with 0.20 wt% Bi₂O₃, which had the largest average grain size, displayed the lowest Pcv.     

The relation between the inner demagnetizing factor of manganese magnesium ferrites and their porosity and permeability

It is shown that the simple relation of direct proportionality between the inner demagnetizing factor and the relative volume of the pores is not sufficient to explain the experimental data obtained on a system of manganese magnesium ferrites. An equation is derived in which the inner demagnetizing factor is directly proportional to the ratio of the relative volume of the pores to the permeability of the sample. The values calculated according to this equation agree well with the experimental results.

---

-

, , - , . , . , , .

     

Influence of saturation magnetization inhomogeneities on the third and fourth moments of the FMR line in polycrystalline ferrites

The influence of saturation magnetization inhomogeneities on the third and fourth moments of the FMR line, which describe its asymmetry and pointiness, is considered in this paper. The computations are performed in the weak and strong coupling approximations between the magnetization fluctuations at different points of the specimen. It is shown that the absorption line shape depends substantially on the shape of the specimen and the magnitude of the porosity. The results of computations are compared with experiment in a broad range of variation of the porosity. The influence of the specimen shape on the shape of the FMR curve is investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 80–84, May, 1982.     

Effect of quenching temperature on the components of the permeability tensor and the complex dielectric constant of microwave magnesium ferrites

We report an investigation of the effect of the quenching temperature (from 900 °C, 700 °C, and for self-cooling) on the components of the permeability tensor and on the complex dielectric constant * of magnesium-aluminum, magnesium-chromium and magnesium-manganese, ferrites of fixed composition. The measuring apparatus and measurement procedure are described and an estimate of the errors is given. It is shown that due to quenching the gyrotropic properties of the ferrites are increased ( falls and _a increases), while the dielectric constant is unchanged. Quenching leads to an increase in the magnetic and dielectric losses.Translated from Izvestiya VUZ. Fizika, Vol. 11, No. 11, pp. 41–47, November, 1968.     

Evaluation of geometrical effect on magnetization loss in GdBCO coated conductor

The magnetization loss density in stacked GdBa₂Cu₃O_7−δ coated conductor was measured using a SQUID magnetometer in a magnetic field normal to the tape surface to investigate the effect of stack on the magnetization loss. The AC loss characteristics are successfully collapsed to a single curve by the normalization at all the measurement temperatures. The losses are similar at high magnetic fields regardless the number of tapes. In addition, the AC loss decreases with increasing the number of tapes in stack at low magnetic fields.     

Effective and accurate single-shot NMR diffusion experiments based on magnetization grating

Current single-shot diffusion methods based on magnetization gratings suffer from low sensitivity due to small rf tip angles and, consequently, from inefficient use of the total equilibrium magnetization. Here, we propose and illustrate the use of a slightly modified form of the magnetization encoding scheme OUFIS for single-shot diffusion experiments. In a detailed theoretical and experimental analysis, we compare the performance of the proposed method to other encoding schemes such as the one-phase or two-phase DANTE and conclude that the OUFIS-based experiment is a superior one. The primary reason is that this scheme allows one to use a larger total pulse area. Hence, one can encode a far larger portion of the initial magnetization into a frequency grating before the onset of various nonlinear effects. In the experimental illustration, we present a single-shot measurement of multicomponent diffusion.     

Influence of Pt thickness on magnetization reversal processes in (Pt/Co)3 multilayers with perpendicular anisotropy

We present a detailed study of the magnetization reversal in perpendicularly magnetized (Pt/Co)₃ multilayers with different values of the platinum interlayer thickness t_Pt. To study the magnetization reversal in our samples we combined measurements of relaxation curves with the direct visualization of domain structures. Magnetization reversal was dominated by domain wall propagation for t_Pt=1 nm and by domain nucleation for t_Pt=0.2 nm, while a mixed process was observed for t_Pt=0.8 nm. We interpret our results within the framework of a model of thermally activated reversal where a distribution of activation energy barriers is taken into account. The reversal process was correlated with the energy barrier distribution.     

ICP-AES法同时测定陶瓷制品铅、镉、铬、钴的溶出量

采用ICP AES法同时测定陶瓷制品铅、镉、铬和钴的溶出量 ,并对 4 %醋酸溶液中仪器入射功率的影响、分析谱线的选择和背景校正及共存元素的干扰等因素进行详细的研究。方法检出限 :铅 6 8μg·L-1;镉 0 18μg·L-1;铬 0 6 1μg·L-1;钴 1 0 μg·L-1。加标回收率为 98%～ 10 4 % ,相对标准偏差为 0 2 7%～1 2 4 %。该法简便快速 ,具有良好的精密度和准确度 ,适用于进出口陶瓷制品的日常检验     

Shape and thickness effects on the magnetization reversal of Py/Cu/Co nanostructures

We present an experimental investigation of the magnetization reversal process in NiFe/Cu(10 nm)/Co circular and elliptical nano-elements with different thickness of the magnetic layers. The results obtained using element sensitive X-ray resonant magnetic scattering (XRMS) were compared with the previous measurements showing that the dipolar interlayer coupling favours the antiparallel alignment of the two magnetization layers at remanance. In the case of circular shape, the increased thickness of the ferromagnetic layers stabilizes the antiparallel alignment of the layers over a wider field range. A similar effect, accompanied by a delay in the onset of the antiparallel alignment, is observed in the case of elliptical nano-elements and applying the external field along the longer axis of the elements, due to the additional shape anisotropy.     

Temperature dependence of the magnetization of canted spin structures

Numerous studies of the low-temperature saturation magnetization of ferrimagnetic nanoparticles and diamagnetically substituted ferrites have shown an anomalous temperature dependence. It has been suggested that this is related to freezing of canted magnetic structures. We present models for the temperature dependence of the magnetization of a simple canted spin structure in which relaxation can take place at finite temperatures between spin configurations with different canting angles. We show that the saturation magnetization may either decrease or increase with decreasing temperature, depending on the ratio of the exchange coupling constants. This is in agreement with experimental observations.     

Magnetoresistance in the magnetization reversal process of micropatterned Co wires

We measured the magnetoresistance (MR) and magnetization of Co wires of various widths in the range from 0.3 to 200 μm. The observed width dependence of some characteristics of MR is attributed to the change of the domain structure. As the width decreased below 1 μm, an abrupt jump appeared in the longitudinal MR. This can be interpreted as due to an abrupt reversal of the overall magnetization. The measured longitudinal MR was compared with the calculation in the Stoner–Wohlfarth model.