Interaction of z component of magnetic field between two samples of GO material in the round rotational single sheet tester (RRSST)

The magnetic properties of two grain-oriented (GO) samples of the same grade were measured under alternating and rotational magnetic flux conditions. Two samples were measured separately and then together in different arrangement to each other. The interaction of magnetic field between two samples were measured by using a coil, which was placed in between. The results show that the _Hz$H_z$ component influence measured magnetic properties in the x–y plane.     

Electromagnetic properties of samarium-substituted NiCuZn ferrite prepared by auto-combustion method

Ni_0.25Cu_0.2Zn_0.55Sm_xFe_2−xO₄ ferrite with x=0.00, 0.025, 0.05 and 0.075 compositions were synthesized through the nitrate-citrate auto-combustion method. These powders were calcined, compacted and sintered at 900 °C for 4 h. Effect of Sm substitution on phase composition, microstructure and relative density were studied. Permeability, magnetic loss and AC resistivity were measured in the frequency range of 1 kHz-10 MHz. Permeability and AC resistivity were found to increase and loss decreased with Sm substitution up to x=0.05. Saturation magnetization also increased up to that substitution limit. Observed variations in electromagnetic properties have been explained.     

Apparent permeability of electrical steel under PWM magnetisation

In recent years much attention has been paid to material performance under pulse width modulation (PWM) excitation conditions, which is of increasing importance to motor applications particularly in energy efficient variable speed drive systems. It is well known that in general, losses increase significantly with reducing modulation index, the increase depending on parameters such as silicon contents, thickness and grain size. The effect of the PWM waveform on permeability has attracted little attention until now. So in this paper its influence on the permeability of electrical steel is analysed and characterised. A prediction approach based on the permeability under sine wave excitation and total harmonic distortion is introduced which results in errors below 10% for non-electrical steel at 1.5 T.     

Remarkable influence on the dielectric and magnetic properties of lithium ferrite by Ti and Zn substitution

The effect of Zn and Ti substitution on the magnetic and electrical properties of Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ ferrites (x=0.0 to 0.30 in steps of 0.05) +0.5wt% Bi₂O₃ prepared by a standard ceramic technique has been investigated. Electrical conductivity and dielectric measurements at different temperatures from 300 K to 700 K in the frequency range from 100 Hz to 2 MHz have been analysed. The variation of the real part of dielectric constant (ε^′) and loss tangent (tanδ) with frequency and temperature has been studied; it follows the Maxwell–Wagner model based on the interfacial polarization in consonance with the Koops phenomenological theory. It is found that the permittivity of zinc and titanium substituted lithium ferrite improves and shows a maximum value ( 1.5×10⁵) at 100 Hz for the x=0.25 sample. The dielectric transition temperature (T_d) depends on the concentration of Ti and Zn in Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄. The saturation magnetization and Curie temperature both decrease with increase in the concentration of Ti and Zn in the ferrite.     

Barium ferrite powders prepared by microwave-induced hydrothermal reaction and magnetic property

We have prepared barium ferrite particles by the microwave-induced hydrothermal method. The crystallization of the barium ferrite particles is promoted within a short time by microwave irradiation because the seeds of barium ferrite having large permeability are rapidly heated through the interaction of barium ferrite with the magnetic component of the microwaves. Crystals having unusually low thickness were obtained compared with the conventional hydrothermal method. The magnetic properties of barium ferrite particles are discussed.     

Effect of Mg substitution on electromagnetic properties of (Ni0.25Cu0.20Zn0.55)Fe2O4 ferrite prepared by auto combustion method

The ferrite compositions of (Ni_0.25−xMg_xCu_0.2Zn_0.55)Fe₂O₄ with x=0.0$x=0.0$, 0.07, 0.13, 0.18, and 0.25 were synthesized through nitrate-citrate auto-combustion method. The as-burnt powders showed the presence of crystalline cubic spinel ferrite with about 19–22 nm crystallite sizes. The resultant powders were calcined at 700 °C/2 h and pressed ferrites were sintered at 950 °C/4 h. The initial permeability, magnetic loss and AC resistivity were measured in the frequency range 10 Hz–10 MHz. The permeability and AC resistivity were found to increase and the magnetic loss decreased with Mg substitution for Ni, up to x=0.18$x=0.18$. The very high permeability in the composition x=0.18$x=0.18$, was due to better densification, lower magnetostriction constant and inner stresses, etc. The AC resistivity of the composition was also highest. The composition would be better than NiCuZn-based material for more miniaturization of multi layer chip inductor.     

High permeability and low power loss of Ti and Zn substitution lithium ferrite in high frequency range

The effect of Zn and Ti on the magnetic, power loss and structural properties of Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ ferrites (x=0.0 to 0.30 in step of 0.05)+0.5 wt% Bi₂O_3, prepared by standard ceramic technique, has been investigated. Complex permeability (μ*=μ′−jμ″) has been analyzed at room temperature in frequency range from 1 to 10³ MHz. It was found an enhancement in permeability with Ti and Zn concentration in Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ and exhibits the maximum value 106 for x=0.20 sample. Complex permeability of these ferrites exhibits stable frequency response up to 7 MHz beyond which the real part decreases sharply and imaginary part increases to have a peak at the relaxation frequency. Power loss measurements have been carried out in induction condition (B=10 mT) in frequency range of 50 kHz to 3 MHz. Power loss has been found to be quite low with the substitution of Ti and Zn in lithium ferrite.     

A novel technique for measurement of core loss in low permeability materials

A survey of existing techniques for measuring core loss in magnetic materials is presented. It is shown that the most challenging combination is a low permeability material at low measurement frequency. Such materials have application in components of power converters, and thus are of considerable technological significance. Measurement difficulties stem from losses in the windings employed, which are difficult to disentangle from loss in the core, as well as the stringent requirements on phase accuracy of measurement instruments. Another practical problem is the large power capacity required of the drive source to achieve significant induction levels. A new resonant measurement setup, which we call the “virtual impedance” technique, is proposed as a solution to these problems. Its utility is demonstrated with measurements of a commercial composite core with permeability 14μ₀ whose low-core loss defeats conventional methods of measurement.     

Tailoring the temperature characteristics of the magnetic permeability of NiZn ferrites

The effect of cobalt addition on the temperature characteristics of the magnetic permeability of NiZn ferrites was studied and a comparison to the respective behaviour of cobalt in NiCuZn ferrites was examined. Cobalt-doped NiZn and NiCuZn ferrites were manufactured by the ceramic route and sintered under various atmosphere profiles. The chemical and morphological characteristics were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The evaluation of the magnetic performance of the sintered ferrites showed that N₂-rich atmosphere profiles during the top temperature and cooling time of the sintering process favour the temperature stability of the permeability in the case of NiZn ferrites, while preserving the losses at low levels. Two mechanisms that take place at the same time are proposed: the change of the Fe²⁺/Fe³⁺ ratio due to the reduction-promoting atmosphere of N₂ in combination with an increase in magnetocrystalline anisotropy and magnetostriction due to the presence of Co²⁺ suggest a useful method to tailor the temperature factor α_F of NiZn ferrites. However, the method cannot be applied in NiCuZn ferrites, as the reduction Cu²⁺-Cu⁺ taking place under N₂-rich atmospheres enhances secondary re-crystallization phenomena, causing a dramatic increase in losses.     

Tailoring the magnetic properties of manganese ferrite with substitution of a small fraction dysprosium for iron

Manganese ferrite nanoparticles with dysprosium (Dy) ions substituted for iron ions have been prepared by using a sol-gel method. Substitution of a small fraction Dy for Fe results in the larger magnetocrystallite anisotropy of MnFe_2−xDy_xO₄ (x=0.2, 0.4) nanoparticles than that of MnFe₂O₄ nanoparticles. The magnetosrystallite anisotropy was enhanced with the increase in the substituted dysprosium content. Combining the result of Mössbauer spectra with ZFC and FC curves, we know clearly that the Dy substitution can modify the anisotropy of MnFe₂O₄ nanoparticles for its strong spin-orbital coupling. Through this simple substitution, we can control the magnetosrystallite anisotropy of the magnetic nanoparticles and make good use of the products according as we need.     

A study of nanosized Ni substituted Co–Zn ferrite prepared by coprecipitation

Nanoparticles of Ni_0.25Co_0.25Zn_0.5Fe₂O₄ with different particle sizes were synthesized by chemical coprecipitation technique. The prepared nanoparticles were characterized and studied by X-ray diffraction, room temperature ⁵⁷Fe Mössbauer spectroscopy and DC magnetization. Increase in annealing temperature leads to inversion of cations from their normal configurations which results in an increase in the hyperfine fields at both tetrahedral A and octahedral B sites. The decrease in saturation magnetization values with an increase in annealing temperature can be attributed to the variation in proportions of superparamagnetic phase and also the redistribution of cations in these ferrite nanoparticles. Variation of coercivity with annealing temperatures can be explained in terms of the size effect.     

Effect of GePt buffer layer on magnetic properties and microstructure of FePt films

We have explored the interlayer diffusion effect of Ge/FePt, GePt/FePt bilayer on the formation of ordered L1₀ FePt phase. In Ge/FePt bilayer, the Ge₃Pt₂ compound was formed during post annealing at 400^oC for 1.0 h. Diffusion between Ge and FePt layer suppres the formation of ordered L1₀ FePt phase. With Ge₂Pt₃ underlayer, the FePt film was ordered at 400 °C and the in-plane coercivity was 9.3 kOe. The ordering temperature was reduced about 50 °C compared to the single layer FePt film.     

The effect of solution temperature on crystallite size and magnetic properties of Zn substituted Co ferrite nanoparticles

In this work zinc substituted cobalt ferrite nanoparticles (Co_0.5Zn_0.5Fe₂O₄) have been synthesized by the coprecipitation method, using stable ferric, zinc and cobalt salts with sodium hydroxide, at different solution temperatures, from room temperature to 363 K. The cobalt-zinc ferrite crystalline phase, the particle size and the morphology of the resulting nanoparticles were studied by X-ray diffraction and transmission electron microscopy. The average crystallite size of each sample was calculated from the broadening of the most intense peak (3 1 1), using Scherrer's formula and the results show crystallite sizes increased from 6 to 8 nm by increasing the solution temperature from room temperature to 363 K respectively. Room temperature VSM measurements show that the prepared nanoparticles have superparamagnetic behavior and did not saturate at maximum field of 800 kA/m. The variation of AC-susceptibility of the samples with respect to temperature was measured and it was found that the blocking temperature increased from 198 to 270 K by increasing the solution temperature from room temperature to 363 K respectively. FTIR spectra of the samples have been analyzed in the frequency range 400-4000 cm⁻¹, which also confirms the results of XRD.     

Preparation and investigation of low firing temperature NiCuZn ferrites with high relative initial permeability

The effects of CuO and V₂O₅ additions and the particle sizes of precursor materials on the microstructure and relative initial permeability of low firing temperature NiCuZn ferrites were investigated. It was found that additions of CuO and V₂O₅ contribute to the grain growth and densification of matrix in the sintering process, which were favorable for increase in relative initial permeability. The relative initial permeability was also strongly affected by the average particle size of precursor materials. Through using precursor materials of 0.8 μm average particle size and adding 10 mol% CuO and 0.20 mol% V₂O₅, for the low firing temperature NiCuZn ferrite, very high relative initial permeability of 1417 can be achieved at the frequency of 1 MHz.     

Measurement of resistivity of soft magnetic laminations at elevated temperatures

The variation of resistivity in soft magnetic materials with temperature is extremely important for applications of electrical machines in aerospace applications. The design of a system for rapid and accurate measurement of the resistivity of Epstein strips under a wide range of temperatures is presented. Two cobalt–iron alloys are assessed up to 200 °C, showing significant differences in their resistivity but almost identical temperature coefficients of resistivity.     

A universal DC characterisation system for hard and soft magnetic materials

A fully automatic system has been designed for the accurate measurement of the DC magnetic properties of soft and hard ferromagnetic materials utilising discrete calibrated instruments in order to provide a traceable calibration route separate from the transfer of standard magnetic test samples. Custom written software is used to operate the system in one of three modes, constant dH/dt, variable dH/dt and a second quadrant demagnetisation curve mode. The first two of these modes are utilised for soft magnetic materials with the second mode varying dH/dt in order to keep dB/dt relatively constant. Both modes use cycle times of between 60 and 300 s and may utilise a variety of test configurations including a bar permeameter, electromagnet, ring samples or Epstein frame. The minimum cycle time and the most appropriate mode is dependent on the particular sample and the effect of this on materials with a large dB/dH is significant. Measurements on soft materials include major BH loop, minor BH loops, first-order reversal curves, remanence, coercivity, normal magnetisation curve, peak permeability and loop area. The third mode is used with an electromagnet to measure the demagnetisation curve of hard magnetic materials up to a maximum demagnetisation field of 1.6 MA/m. The measurement algorithm modulates dH/dt depending on dB/dt and incorporates holdback in order to accommodate rare earth materials which exhibit high viscosity.     

Magnetic properties of nanostructured MnZn ferrite

Mn_0.5Zn_0.5Fe₂O₄ nanoparticles (10-30 nm) have been prepared via mechanochemical processing, using a mixture of two single-phase ferrites, MnFe₂O₄ and ZnFe₂O₄. SQUID measurements (field-cooled magnetization curves and hysteresis loops) were performed to follow the mechanically induced evolution of the MnFe₂O₄/ZnFe₂O₄ mixture submitted to the high-energy milling process. The resulting single MnZn nanoferrite phase was characterized by SQUID (M-H curve), Faraday balance (M-T curve) and transmission electron microscopy. The magnetic characteristics of the mechanosynthesized material were compared with those of bulk Mn_0.5Zn_0.5Fe₂O₄. It was found that the saturation magnetization of nanostructured Mn_0.5Zn_0.5Fe₂O₄ (87.2 emu/g) is lower than that of the bulk Mn_0.5Zn_0.5Fe₂O₄, but, the Néel temperature of the sample (583 K) is higher than that of the bulk Mn_0.5Zn_0.5Fe₂O₄.     

Laser-induced dry chemical etching of Mn-Zn ferrite in CCl2F2 atmosphere

Maskless etching of Mn-Zn ferrite in dichlorodifluoromethane (CCl₂F₂) by Ar⁺-ion laser (514.5 nm line) irradiation has been investigated to obtain high etching rates and aspect-ratio of etched grooves. The etching reaction was found to be thermochemical. High etching rates of up to 360 m/s, which is about one order of magnitude higher than that in a CCl₄ gas atmosphere and even higher than that in a H₃PO₄ solution, have been achieved. A maximum aspect-ratio of 6.9 was obtained.     

Magnetic and Mössbauer studies of Ni substituted Li-Zn ferrite

Li-Zn ferrites substituted with Ni having the compositional formula Li_0.4−0.5xZn_0.2Ni_xFe_2.4−0.5xO₄ where x=0.02?x?0.1 in steps of 0.02 were fabricated by the citrate precursor method. This method has been employed to get nanosized particles and good magnetic properties. The spinel phase structure of the prepared ferrites was confirmed by XRD analysis. The effect of Ni concentration on magnetic properties such as saturation magnetization and Curie temperature were investigated. A good knowledge of these magnetic properties is desirable from application point of view. The values observed are large and both quantities were found to decrease with substitution. The saturation magnetizations were found to vary from 78 to 94 emu/gm while the Curie temperature which limits the operating temperature of the system ranges between 563 and 584 °C. Mössbauer data were also recorded at room temperature and the hyperfine parameters like isomer shift, quadrupole splitting and internal magnetic field estimated. The results obtained and mechanisms involved are discussed.     

Polar Kerr rotation spectra in yttrium iron garnet and lithium ferrite: A comparative study

Polar Kerr rotation (PKR) spectra in the range 2.0–5.7 eV at 295 K of lithium ferrite and yttrium iron garnet (YIG) single crystals are reported. The spectra show more details and cover a more extended energy region than those published so far. The interpretation of the spectra is based on the assumptions that 1) PKR is an odd function of the sublattice magnetic moments 2) the origin of PKR in both compounds is of similar nature, the differences due to the different crystal structures (garnet and spinel) being less important. The calculated PKR sublattice components show some similarities in their energy dependences, the magnitude of the tetrahedral sublattice component being higher than that of the octahedral one. The components were used in the calculation of the PKR spectra in diamagnetically substituted yttrium iron garnet (J. Appl. Phys.49, 2212, 1978). The results correctly predict the trends observed experimentally.