MnNi-ferrite (Mn_1-xNi_xFe₂O₄) thin films were prepared on a glass substrate by vacuum evaporation and solid reaction. Their crystallographic structures, magnetic properties, and electrical conductivities were investigated. The lattice constant of MnNi-ferrite films decrease with increasing composition rate x. The coercive force H_c is minimum at x=0.5. Saturation magnetization I_s and Curie temperature T_c are defined as linear function of variable x. However, the saturation magnetization tends to decrease with increasing x, while the Curie temperature shows the opposite tendency. It is thought that the electrical conductivity is caused by the hopping mechanism of small polaron according to Mott's theory.

抄録全体を表示

  Rf sputter deposited lithium zinc ferrite films were observed to crystallize with spinel structure for annealing temperatures (T_a) of 600 °C and above. The as-deposited film showed a 4πM_s value of the order of 628 emu/cc. The 4πM_s values gradually increased as a function of T_a. The film annealed at 850 °C, showed a maximum value of 94 % of the corresponding bulk value. The remanence ratio also showed a rise as T_a increased and showed a value of 0.52 at T_a=850 °C. While, coercivity value increased till T_a=750 °C and decreased thereafter. On the otherhand, 4πM_s, H_c and M_r/M_s values of the samples annealed at various time duration, at a T_a of 750 °C, did not vary much in the entire time range.

抄録全体を表示

  Epitaxial thin films of Ni-ferrite were prepared on C-plane sapphire substrates by pulsed laser deposition in high vacuum. When deposited at oxygen pressures of greater than 1 × 10⁻⁶ Torr, the films crystallized in NaCl-type crystal structure at T_s≤100°C, while in spinel-type crystal structure at T_s≥150°C. The low temperature growth of the ferrite thin films was ascribed to the high kinetic energy of ablated particles at low oxygen pressures and to the low deposition rate of the films. X-ray phi scan and reflection high-energy electron diffraction analysis showed that the spinel ferrite films epitaxially grew with (111) texture normal to the film plane and in-plane alignment of NiFe₂O₄ [110] parallel to sapphire [1100]. The films had an excellent crystallinity as well as a good surface smoothness as grown at T_s ≥ 200°C.

抄録全体を表示

  In order to develop good backlayer for the Co-Cr perpendicular magnetic recording media, crystalline films of spinel, (Fe,M)₃O₄(M=Ni and Zn) were prepared on glass substrates by spin-spray ferrite plating method. Reaction and oxidizing solution were sprayed in the reaction chamber in which the substrate is rotating. The reaction was influenced by concentration of reaction solution(R_c) and oxidizing solution(O_c), the flow rates of the reaction solution(R_f) and oxidizing solution(O_c), reaction temperature(T) and rotation speed of substrate(S_r). Under the condition where R_r, O_f=60[mℓ/min], T=90[°C] and S_r=150[rpm], effect of R_c and O_c on the ferrite plating reaction were studied in aspect of chemical composition, crystallographic and magnetic properties. In the composition of Ni_0.34Zn_0.66Fe₂O₄, we have the stable crystallographic and magnetic properties.

抄録全体を表示

  Barium hexafenite films have been deposited by rf diode sputtering on (111) gadolinium gallium garnet (GGG) substrates chemically surface-treated and with epitaxial thin layer of α-Fe₂O₃. X-ray analysis showed that the films on the chemically treated substrates grew with c-axis oriented normal to the film plane but two types of in-plane epitaxial alignment. When deposited on a 25-nm α-Fe₂O₃ layer, the films exhibited predominantly (0001) textured growth and in-plane epitaxial alignment of Ba hexaferrite [1-100] parallel to α-Fe₂O₃ [2-1-10] and therefore parallel to GGG [1-10]. This textured growth was associated with the surface smoothness of the α-Fe₂O₃ underlying layer.

抄録全体を表示

  A deposition of c-axis oriented hexagonal barium ferrite thin films was attempted by means of an alternate periodic deposition of S (Fe₂O₃) and R(BaFe₆O₁₀) layers. All of the films obtained in this study had (001) texture, although they also contained a spinel phase with (111) orientation. Crystallite size in the film depends on the ratio of the thickness of the S layer to that of the R layer, and increased as this ratio increased. M-type barium ferrite (BaM) thin films with excellent c-axis orientation were obtained when the thickness of the S and R layers were 4.7 Å and 6.9 Å, respectively. We also tried to form the W-type barium ferrite (BaW) film by depositing S layers 9.3 Å thick and R layers 6.9 Å thick altemately. The film, however, did not contain the BaW crystallites and was a mixture of BaM and the spinel-type crystallites.

抄録全体を表示

  In this study, we used computer simulation to investigate changes in the composition of hexagonal barium ferrite films deposited by a facing target sputtering. The iron content in the film increased as the sputtering gas pressure increased and reached a maximum value at a certain gas pressure. These changes in the film composition were explained as follows; sputtered particles scatter when they collide with sputtering gas atoms, and this scattering changes a ratio of the particles reaching the substrate. When the substrate was located to the side of the target as in a facing target sputtering system, this scattering resulted in an increase in the amount of sputtered particles arriving at the substrate, although too much scattering caused the amount to decrease. Since this gas scattering depends significantly on the atomic mass of the sputtered particles, the gas pressure dependence of the amount of the iron atoms arriving differs considerably from that of the amount of barium atoms arriving. This difference leads to the changes in film composition.

抄録全体を表示

  Strontium hexagonal ferrite (SrM) thin films were prepared with a dc magnetron sputtering system, and the crystal structure and magnetic properties were studied. It was found that structural and magnetic properties of the films prepared at the substrate temperature (Ts) of 600°C were affected by partial oxygen pressure (Po₂) as compared with those of the fiim prepared at Ts of 550°C. The coercivity of each film prepared at Ts of 550°C was about 5kOe in the perpendicular direction, although that of the films prepared at the Ts of 600°C and Po₂ of 10% was about 2kOe with preferential orientation of c-axis was observed. The grain size of the films prepared at the Ts of 600°C was larger than that of other films. It could be considered that growth of the grains lead to the decrease of the coerdvity.

抄録全体を表示

  A pulsed laser deposition was successfully applied to obtain BaFe₁₂O₁₉ and BaFe₁₈ O₂₇ hexaferrite films on sapphire (0001) substrates. The (001) epitaxial BaFe₁₂O₁₉ films with atomically smooth surfaces were grown at 780°C and oxygen atmosphere pressure of 100-200mTorr. The preparation of a single-phase BaFe₁₈O₂₇ films required lower oxygen pressure. The decrease of the magneto-optical effect and the magnetization of BaFe₁₈O₂₇ film to BaFe₁₂O₁₉ films is due to the imperfect crystallization.

抄録全体を表示

  High bismuth and gallium-substituted yttrium-iron-garnet (Bi:Ga:YIG) films were prepared by two-step gel coating on glass substrates. The gel-solutions were synthesized by the “glycol gel process” utilizing ethylene glycol and nitrates dissolved in distilled water as the liquid precursor. Thin garnet layers about 0.1μm thick with the composition Bi₂YFe_3.6Ga_1.4O₁₂ (compensation composition at room temperature) were first formed on glass substrates, upon which thicker garnet films with larger amount of Bi-substitution (Bi_xY _3-xGa_YFe_5-YO₁₂, where x=2 to 2.8, and y=0 to 1) were successively formed. By this technique, polycrystalline single-garnet phase films up to x=2.7 could be obtained. These films exhibied perpendicular magnetization with good squareness in hysteresis loops. Furthermore in order to seek for low temperature synthesis of garnet films, crystallization temperature Tx of garnet was examined for the series of compositions, Bi_2.2Y_0.8Ga_YFe_5-YO₁₂, y=1.0 to 1.6. It was found that Tx is lowered down to 500°C at y=l.4.

抄録全体を表示

  La_1-xSr_xMnO₃ films were deposited on SiO₂/Si substrates by using the facing target sputtering apparatus with La_0.76Sr_0.24Mn_0.78O₃ targets in mixture gas of Kr and O₂ or Ar and O₂. For films deposited in Kr+O₂, (111) orientation was observed, while (110) orientation was preferential for films deposited in Ar+O₂. 4πM_s of as-deposited films was very small at most 0.17 kG, of which the value corresponded to 1/18 of that of targets. It increased up to 2.4 kG after post-annealing at 1000°C in O₂, while the films prepared under same conditions in Ar+O₂ exhibited relatively small 4πM_s of 1.6 kG.

抄録全体を表示

  We provided formation conditions of (001)-oriented epitaxial Fe_2-XTi_XO₃ (X=0.0∼1.0) films by activated reactive evaporation technique. Structural and magnetic properties of the films depended on both the composition and the substrate temperature. The lower substrate temperature below 600°C brought about disordered Ti and Fe ions within the hexagonal oxygen lattices having the same symmetry as hematite (R3c). While the films with X≧0.75 prepared at higher temperature of 700°C were formed into the ordered structure as ilmenite (R3). The ordered films with 0.75≦X<1.0 were strong ferrimagnetic though the spontaneous moments were fairly small than the ideal values.

抄録全体を表示

  Nanocrystalline ε-Fe₃N nitride particles have heen synthesized by chemical route. ε-Fe₃N crystallizes in hexagonal structures with an overall lattice expansion because of ultrafine nature of the particles. Chemisorption of oxygen results In the formation of magentically dead oxide and/or oxynitride layer at the surface of the particles. The reduced magnetization in ε-Fe₃N particles is attributed to surface oxidation, superparamagnetic relaxation and spin canting at the surface of the particles. Curie temperature, T_c decreases with the decrease in particle size. Mosshauer study of ε-Fe₃N particles exhibits the coexistence of ferromagnetic and superparamagnetic particles and corroborates the magnetic properties.

抄録全体を表示

  The magnetic and structural changes of [1.2nm Au/0.3nm Fe]₁₈₀ multilayers (MLs) induced by Ar ion irradiation and thermal annealing have been investigated by Conversion Electron Mössbauer Spectroscopy (CEMS). The distributions of hyperfine fields (H_hfs) estimated from CEM spectra indicate the decrease of the H_hfs due to the breaks of the Fe layer structure in Au/Fe MLs by the ion irradiation and the thermal treatment. The thermal annealing causes the paramagnetic doublet peaks due to Fe clusters and the split six-line peaks arising from metallic α-Fe phase. However, the ion irradiation does not induce metallicα-Fe phase because of the mixing effects by ion irradiation.

抄録全体を表示

  MnAs epilayers were grown on GaAs (001) substrates by molecular-beam epitaxy with the supply of atomic hydrogen (H•). X-ray diffraction and reflection high-energy electron diffraction characterizations revealed that the growth directions were along the [1100] direction for the epilayer grown with H•, and along both the [1100] and [1101] directions for the epilayers grown with/without hydrogen molecules (H₂). Atomic force microscope observations showed that the faceted mounds elongated along the GaAs [110] direction were only observed for the epilayer grown with H•, although large three-dimentional islands were observed on the elongations along the GaAs [110] direction for the epilayers grown with/without the supply of H₂. The results indicate that the irradiation of H• enhances the growth of MnAs epilayers along the single direction and improves the surface smoothness.

抄録全体を表示

  Polycrystalline Co films of hcp single phase were produced on glassy substrates by Gas-Flow-Sputtering technique. The hcp Co films were obtained at the substrate temperatures below 620 K and the mixture of hcp and fcc phases was formed above the temperature. Two kinds of preferred orientations of texture, where (00.1)_hcp or (10.0)_hcp plane was parallel to the film plane, were observed.

抄録全体を表示

  By inserting only 0.75 nm-thick Cu underlayer between the IrMn/CoFe/Cu/CoFe spin-valve stack and Ta underlayer, the MR ratio was about 1.8 times as large as that without the Cu layer. XRD and magnetic measurements suggest that the Cu “islands” formed in the initial growth stage modify the interfaces of the spin-valve, resulting in the enhancement of the spin-dependent scattering. When the Cu thickness (t) was larger than 1.5 nm, the MR ratio and coercivity of the free layer were increased and decreased, respectively, in comparison with those of t=0 nm. This was due to the considerable increase in the crystallinity of the spin-valve films. Namely, Cu is expected to function as the buffer “layer” in this thickness range.

抄録全体を表示

  Dependence of magnetoresistance (MR) on copper layer thickness δ _Cu is investigated in electrodeposited CoCu/Cu and CoNiCu/Cu multilayers grown onto vacuume-deposited copper base layers. The relation between the MR ratio and δ _Cu is found to depend on the plating conditions such as a plating current for the magnetic layer or the concentration of magnetic ions in the electrolyte. In some cases, markedly grown columnar structures are observed in SEM and TEM images. The columnar structures of the multilayer grown on the vacuume-deposited copper are found to be more distinguished than those grown on electropolished copper plates. These observations suggest that the formation of the columnar structure and the resulting surface roughness might affect the MR ratio.

抄録全体を表示

  Fe: 2.0 nm/ Ag double layered films were continuously prepared by evaporation method with electron beam heating equipment on glass substrate. The thickness of Ag under-layer film was changing from 0 to 200.0 nm. The composition and surface morphology of Fe/Ag double layered film were investigated by measuring with the AES spectra and AFM images. When the under-layer thickness is 50.0 nm, the saturation magnetization Is of the film has maximum value which is 20 kG, and the surface morphology seems more uneven shapes than any other films. When under-layer thickness is 20.0 nm, the coercive force Hc has minimum value which is 11.8 Oe. For Fe film of 2.0 nm thickness with under-layer, the surface morphology of the films and the stress in the under-layer are related to the magnetic properties.

抄録全体を表示

  The magnetic propeties of SmCo layers on Cr underlayer prepared by facing targets sputtering (FTS) and DC magnetron sputtering (DCMS) system at various Ar gas pressure, P_Ar, were studied. The surface micrographs of Cr underlayer deposited with each system showed that the grain size was different while that of each SmCo/Cr film was almost same. The shape of M-H loops of the films were well squared. The coercivity and the saturation magnetization of SmCo layer on Cr underlayer prepared by FTS at P_Ar of 0.27 Pa were about 240 kA/m and 0.61 Wb/m², respectively, which are larger than those of SmCo layer on the Cr underlayer prepared by DCMS. It was found that the magnetic switching volume was changed with P_Ar and had a minimum value of 4.1 × 10^-24 m³ at P_Ar of 0.27 Pa.

抄録全体を表示

  The effect of substitution of Fe for Co on the magnetic and magneto-optic properties of Co/Pd multilayers is studied over a range of composition and sputter gas pressure. The substitution of Fe for Co leads to a decrease in the coercivity and to a degradation in the shape of M-H loop. The degradation in the shape of M-H loop has been explained on the basis of two step magnetization reversal process. Similar to Co/Pd multilayers, the coercivity increases with sputter gas pressure and the magnetization switching mechanism of the multilayers changes with the sputter gas pressure of the underlayer. The Kerr rotation at 400nm decreases with Fe and the Curie temperature does not show much variation with the addition of Fe up to 24at%.

抄録全体を表示

  The dependence of the magnetic properties of Fe-N and Fe-Ti-N thin films on partial nitrogen pressure (P_N2/P_Total) during sputtering was studied, and annealing effect of Fe-Ti-N thin films was investigated. Thin films were prepared with a dc magnetron reactive sputtering apparutus, using a composite type of target in Ar and N₂ mixed gas. The comparison between the properties of Fe-Ti-N and Fe-N thin films showed that the coercivity (Hc) of Fe-Ti-N thin films was lower than that of Fe-N thin films as a whole. The minimum value of Fe-Ti-N films was 2.3 Oe in easy magnetization direction and 1.25 Oe in the hard magnetization direction at P _N2/P_Total of 2.5 %. The annealing of Fe-Ti-N films decreased the minimum value of Hc to about 1.0 Oe at P_N2/P_Total of 2.5 %.

抄録全体を表示

  The MgO/Cr₇₀Al₃₀/Fe₁₉Ni₈₁ layered films with different MgO buffer layer thicknesses were prepared on (100) Si substrates in order to alter the grain size and the lattice constant of the antiferromagnetic layer. The exchange-coupling field was found to consist of the intra-grain intrinsic exchange-coupling field and the inter-grain exchagne-coupling field. The former field is inversely proportional to the product of the lattice constant and the grain size, The latter field changes its sign by changing the thickness of the MgO buffer layer.

抄録全体を表示

  The magnetic properties of ultrafine copper ferrite particles have been investigated, and to examine the possibility of enhanced coercive force in ultrafine particles by Jahn-Teller effect. Ultrafine copper ferrite particles prepared by coprecipitation have been heated at various temperatures. X-ray diffraction patterns indicate that the crystal structure of ultrafine copper ferrite particles obtained by heating at a temperature above ∼400°C is tetragonal with the axial ratio (c-a)/a of∼5.8%, which is nearly equivalent to that of the bulk material, while that of the ultrafine particles obtained by heating at a temperature below ∼300°C is cubic. The maximum coercive force obtained in this work has been ∼1500 Oe at heating temperature of∼700°C. It has been believed that Jahn-Teller effect obviously occur in ultrafine copper ferrite particles with the particle size of 12∼40 nm. The enhanced coercive force can be mainly attributed to uniaxial magnetic anisotropy produced by the crystal distortion.

抄録全体を表示

  Ultrafine monophasic single domain CoFe₂O₄ particles of 5.80-62.50 nm having surface area 180.50-18.2 m²/g were synthesized by citrate precursor technique. The smaller particles form the chain like clusters due to strong magnetic dipolar interactions. Reduced satuarion magnetization was attributed to superparamagnetic fraction and spin noncollinearlity at the surface. The maximum in magnetization just below T_c (magnetic anomaly) was exhibited by superparamagnetic particles; it was related to the surface/shape anisotropy and well described by the relation, (σ_max − σ_min)/&sigma;_min=±(d/d_o)^-n with 1/n=0.1159±0.013 nm and d_o=6.26nm corresponds to 6.98nm superparamagnetic particle size.

抄録全体を表示

  Lead-hexaferrite (PbFe₁₂O₁₉, shortly PbM) fine particles ranging from 0.038 to 0.6 μm in diameter, were synthesized by mist pyrolysis. Mist was generated by an ultrasonic nebulizer operated at f=2.6 MHz from an aqueous solution of lead (II) nitrate and iron (III) nitrate dissolved in distilled water. Single phase PbM particles were directly obtained from the solution with the molar ratio(Pb)/(Fe)=0.13∼0.23 of the solution, which is slightly high Pb concentration of the stoichiometric PbM composition (i.e.(Pb)/(Fe)= 0.083), after the mist passed through an electric furnace kept typically at 800°C. The particle shape was apparently sphere, but they were the agglomeration of finer PbM particles of 0.01μm in diameter. The magnetic properties at room temperature are: σ_s (saturation moment) = 56 emu/g, _IH_c (coercivity)= 4∼5 kOe, and (BH)_max==0.7∼0.9 M G·Oe, which are the same magnitudes as in the reported values of PbM. Monocrystalline PbM particles were obtained by annealing amorphous particles at 1000°C in a short duration (∼5 min.) in air.

抄録全体を表示

  Nanosized particles of SrFe₁₂O₁₉ have been synthesized by citrate precursor technique having Fe/Sr ratios of 12.0 to 9.0. XRD, SEM, BET surface area, magnetic and Mössbauer studies were carried out for all these particles. Mössbauer study reveals the change in hyperfine parameters with decline in párticle size and Fe/Sr ratios. A coercive force of 6500 Oe is obtained for the SrFe₁₂O₁₉ particles with Fe/Sr ratio 10.8 having 116 nm BET particle size. This value is one of the highest value reported for isotropic SrFe₁₂O₁₉ samples. A considerable enhancement in T_c from the bulk value of 750 to 883K was observed for XRD particle size of 20 to 5.7nm. The shift in T_c is well defined by the finite size scaling formula [T_c(D) - T_c(∞)][T_c(∞)]^-1=±(D/D_o)^-1/v with v = 0.75 ± 0.02 and D_o = 1.52nm.

抄録全体を表示

  Nanometer particles of yttriumiron garnet (Y₃Fe₅O₁₂ or YIG) have been prepared by a chemical coprecipitation method and subsequent heat-treatments, and their magnetic properties have been explored by using magnetization measurements and Mössbauer spectroscopy. Significantly reduced saturation magnetizations of YIG small particles obtained by the coprecipitation method can be attributed to a possible modification occurring in exchange interaction schemes of YIG as a bulk effect (reduced exchange interactions) that can be caused by defects in Fe-site (vacancy or/and Y ions occupations) introduced in particle during this particular processing as well as the presence of recalcitrant spins (magnetically very hard characteristics) on the surface shell of a particle.

抄録全体を表示

  The as-quenched silicate glasses containing iron oxides obey the magnetic structure model that both magnetic clusters and free iron ions in the glass matrix bear the magnetism. The annealing of 20CaO·20SiO₂·7Fe₂O₃·6FeO glasses at 973K in vacuum produced iron oxide particles with the diameter of 2.5-11.5nm. The phase was identified to be Fe³⁺(Fe³⁺_1.30Fe²⁺_0.55V_0.15)O₄ in the inverse spinel structure. The growth of particles proceeded predominantly by diffusion of Fe³⁺ ions. The particles exhibited super-paramagnetism and the effective anisotropy energy constant was inversely proportional to the particle diameter. The thermoremanent magnetization measurements show non-interacting particles as explained by Neel's theory. On the other hand, ac susceptibility measurements show interacting particles as interpreted by Dormann's model. The results indicate the different sensitivity of the above two types of measurements on the superparamagnetic relaxation of particles.

抄録全体を表示

  Silicate glass system rich in Fe²⁺ and Fe³⁺ with their various molar ratio is prepared, and the magnetic behaviors are studied systematically. The glasses basically behave as superparamagnet, which is attributable to deposited magnetite clusters. As the temperature drops, however, drastic shift of the field for ESR absorption as well as ferromagnetic type Curie-Weiss law in the dc susceptibility are observed. The novel characteristics is revealed to be caused by magnetic boundary intemction between the cluster and the surrounding amorphous region. As for the specimens with modemte component region (ratio from 0.39 to 0.66 of Fe²⁺ to total Fe ions), the shifting ESR signal also shows an anomaly around 100K caused by Verwey transition of magnetite, indicating that Verwey transition occurs even in the super fine scale about 40∼55 Å.

抄録全体を表示

  The disk characteristics of granular media comprising Co-Pt and SiO₂ have been examined to demonstrate their high-density recording capabilities. The grain size increased when RF-bias was applied during sputtering. A coercivity was 2 kOe at a magnetic moment (Mrt) of 0.4 memu/cm² and a Co-Pt content of 50vol.% when a Cr seed layer used. The mean grain size was less than 10 nm and the grains were thoroughly isolated in the SiO₂ matrix. The normalized media noise was less than 10^-2μm^1/2μV_rms/μV_pp up to 200 kfci. Transition patterns of more than 200 kfci were clear at a track-width of 1μm. The surface roughness was similar to that of a bare glass substrate. No degradation in magnetic properties was observed after 1000 hrs. in an 80°C-75%R.H. environment.

抄録全体を表示

  Annealing effects on the magnetic properties and magnetoresistance (MR) are examined for Co/Au and Co/Ag multilayers (ML's) prepared on glass substrates. In these films, the pseudo-granular type GMR appears. When the Co/Au ML's are annealed at 300°C, the MR ratio and the field sensitivity of MR increase, because the number of superparamagnetic Co grains in Au layers increases and their grains grow on annealing. On the other hand, the MR ratio of the Co/Ag ML's is not varied much by annealing, while the sensitivity becomes larger, and reaches 7.6%/kOe. This value is higher by a factor of 3 than that for a Co-Ag heterogeneous film prepared by sputtering.

抄録全体を表示

  In heterogeneous Fe-, Co- and Fe₃₈CO₆₂-SiO₂ films prepared on glass substrates, the magnetic and transport properties have been examined. The resistivity increases drastically with decreasing volume fraction of the transition metal, and the transport property changes from the metallic to the tunneling conductivity at the percolation points. At these points, the magnetism also varies from the ferromagnetic to the superparamagnetic, which causes the tunneling giant magnetoresistance (MR). The magnetization and MR curves have been systematically analyzed well with the summationof two Langevin functions, corresponding to the two type superparamagnetic grains having the different sizes. The maximum MR ratios are about 3.6% for Fe-, 3.8% for Co- and 4.4% for Fe₃₈Co₆₂-SiO₂. These values are discussed with the degree of the spin polarization.

抄録全体を表示

  The paper describes the direct synthesis of magnetic nanocomposites of γ-Fe₂O₃ in presence of varying concentrations of zinc ions. Infrared, Mössbauer and pH measurement studies on these materials reveal the effect of zinc ions on clustering of the iron oxide particles resulting in nanosize particles of critical size to give paramagnetic and/or ferrimagnetic phases.

抄録全体を表示

  In the design of high frequency high efficiency dc power supply, core losses in magnetic components becomes an important design consideration. A simple in-house experimental setup consisting of an impedance analyzer and a PC computer for determining core loss of Mn-Zn magnetic materials under sinusoidal excitation is proposed here. The power requirement for this measurement is small. The method using compensating technique provides reasonably accurate result as the determination of core loss is not significantly affected by the parasitic of the measuring apparatus especially when measurement is done at high frequency.

抄録全体を表示

  The real part of the complex initial permeability, μ_i';, of MnZn ferrites having the μ_i'/μ_o values above about 3000 begins to fall at a certain frequency below 1 MHz. This phenomenon has been explained by the domain wall resonance or the rotational resonance. We analyzed the permeability spectra as the behavior of the electromagnetic wave derived from the cross section radius, γ, the resistivity, ρ, and the complex permittivity, ε. The μ_i'; spectrum often had a peak at a certain frequency followed by a rapid fall. The calculated peak frequencies using the formulas of both the resonance were much higher than the measured values. However, the calculated spectrum using the three parameters, γ, ρ and ε also explains the measured curve with a peak and a following rapid fall. The μ_i' spectrum is thereby determined by the individual sample dimension and the macroscopic electromagnetic properties.

抄録全体を表示

  The dispersion phenomena of spinel ferrite due to relaxation can be observed at some frequency range, and this is related with the ferrite composition and their initial permeability. In this work, the Cole-Cole plots for NiCuZn ferrites are presented to describe its relaxation process with μ'. versus μ" spectrum. It is found that the relaxation process with a semi-circle curve of complex permeability is characterized by the magnitude of initial permeability.

抄録全体を表示

  Reduction of losses of Mn-Zn ferrites is of great importance to develop power supplies reduced in size and weight.For this requirement many attempts to study loss characteristics have been carried out, however, all contributions of each loss factor have not been made clear yet. In this study the eddy current losses are assumed to be expressed as a classical formula, proportional to the cross sectional area of the sample, squares of frequency and magnetic flux density and inversely proportional to AC resistivity. On this assumption the eddy current losses contribute less than 10% of total losses at 100kHz and 200mT. Furthermore the residual losses have proved to be in direct proportion to the hysteresis losses and the ratios of two components depend on frequencies and temperatures of measurement and also on grain size of the core samples.

抄録全体を表示

  Exciting ferrite cores in a high frequency range, the real part of the complex permeability deteriorates and the imaginary part of it has a peak after starting the deterioration. For a certain Mn-Zn ferrite material, we find that the frequency characteristics of the complex permeability depend on core size, i.e. the real part decreases more sharply with an increase in frequency when core size becomes larger. In order to demonstrate this phenomenon, an electric circuit with a capacitor is assumed for a ferrite core. It is examined whether its capacitance correlates with the magnetic loss or the eddy current loss. As a result, it is found that the core size dependence of the frequency characteristics is caused by the dielectric currents flowing in the cores.

抄録全体を表示

  In this study, the composition and permeability for low temperature sintered NiCuZn ferrites were investigated and the effect of permeability on the Q_Max frequency of multilayer chip inductors was carried out. It has been observed that the Fe₂O₃ deficiency for low temperature sintering condition was decreased with NiO contents of NiCuZn ferrites. The permeability of NiCuZn ferrites can be controlled in the range of 12∼562 with the variation of NiO and Co₃O₄ contents. The Q_MAX frequency of NiCuZn ferrites was decreased linearly with permeability increased. The relation between the Q_Max frequency(Y) and permeability(X) was expressed with the following empirical equation, logY=4.2-1.41ogX.

抄録全体を表示

  Complex permeability (μ^*=μ'-iμ")and electrical resistivity of permalloy and its composite materials(permalloy powder and Polyphenylene Sulfide resin) have been investigated in the frequency range from 100Hz to 2GHz at room temperature. In a bulk permalloy, a frequency dispersion takes place at about 300Hz; both μ' and μ" decrease with increasing frequency above this frequency. In permalloy composite materials, the low frequency permeability μ' decreases and the dispersion frequency increases with a decrease of permalloy content which can be seen in the ferrite composite materials. Low frequency electrical resistivity shows a drastic increase at about 40vol% with decreasing permalloy content. Below this content region, resonance type frequency dispersion appears in permeability spectra.

抄録全体を表示

  Frequency dependence of power loss of Mn-Zn ferrite was investigated in relation with the complex permeability in the frequency range 10 kHz - 5 MHz and the temperature range 23 - 120°C. The residual loss, Pr, occupies more than half of the total power loss at frequency above 1 MHz and exhibits a close relationship with the imaginary part of the permeability, μ”. Experimental frequency characteristics of μ” can be explained by the dimensional resonance of the electromagnetic wave calculated by the Maxwell equations assuming the homogeneous ferrite body. We investigated the microstructure and the electromagnetic properties preferable for the power ferrite with low loss at high frequency.

抄録全体を表示

  In this paper, the temperature dependence of eddy current loss and residual loss is investigated with relationship between (P_B-P_h) and electrical resistivity at the temperature region except T_min which hysteresis loss attains minimum. Consequently, a quantitative separation of each loss has been made possible not only at T_min but at any temparature. Pe increases with increasing temperature. The temperature dependence of the eddy current can be concluded to be caused by the change in the electrical resistivity with temperature.

抄録全体を表示

  Magnetic and dielectric properties of polycrystalline NiZnSc-ferrites with simultaneous substitutions of zinc and scandium have been investigated. The dielectric behaviour is found to be unusual and parallel to that reported earlier first in MnZn-ferrites and recently in NiZn-ferrites. The dielectric constants remain of the order of 10⁴ even at frequencies above 1 MHz while showing flux reversal accompanying dielectric loss peaks at around 9 MHz. As the frequency of dielectric loss peak coincides with the maximum of magnetic loss for each sample and as the samples exhibit fairly high values of low frequency permeability, an effort has been made to find out whether the observed unusual dielectric behaviour is due to dimensional resonance. Resonance frequency for each case has been estimated theoretically and a comparison of the same with the experimental results confirms the presence of dimensional effects.

抄録全体を表示

  The electrical and magnetic properties of WO₃-added NiCuZn ferrites, (Ni_xCU_0.2Zn_0.8-xO)_1.02(Fe₂O₃)_0.98 sintered at a low temperature, were studied. It was found that the addition of small amount(below 1wt.%)of WO₃ improves their electrical and magnetic properties. Q-factor at 10 MHz increased by increasing of electrical resistivity with no significant change in permeability. Resonance frequency(f_{μ" max}) in WO₃-added (Ni_0.2Cu_0.2Zn_0.6O)_1.02(Fe₂O₃)_0.98 ferrites was moved into the high frequency region. When the sintering time was changed from 5 hrs to 12 hrs, initial permeability and Q-factor increased.

抄録全体を表示

  We have obtained. sintered ferrite with almost-complete shape and high dimensional accuracy by adding metallic Fe, NiO, ZnO, and CuO to Ni-Zn-Cu series ferrite. To confer this non-shrinking property on ferrite, we controlled its shrinkage during the sintering process, utilizing the expansion caused by the oxidation and complex chemical reaction of densely mixed-in metallic Fe, NiO, ZnO, and CuO. The new non-shrinking ferrite is of single-phase, high-density sintered type with an extremely low expansion/shrinkage coefficient during the sintering process of 0-0.5%. Its magnetic characteristics and mechanical strength are virtually identical to those of conventional sintered ferrite.

抄録全体を表示

  The effects of sintering temperature and oxygen partial pressure on the electromagnetic properties of Mn-Zn ferrites were investigated. The grain size increased with increasing sintering temperature. The power loss at 100kHz decreased, while the power loss at 500kHz increased as the grain size increased with sintering temperature. Sintering with low oxygen partial pressure at 1150°C resulted in high density and initial permeability, and decreased the power loss at 100kHz and 500kHz. The oxygen partial pressure lower than 10^-2 atm. during heating, significantly suppressed the hysteresis loss. However, the oxygen activity did not affect the grain size of the sintered cores.

抄録全体を表示

  Barium ferrite particles were prepared by coprecipitation and calcination in NaCl flux, called the salt-melt method. Three different compositions for preparing barium ferrite particles were designed. Right after coprecipitation, the composition I contained α-Fe₂O₃, δ-FeOOH, Fe₃O₄, Ba(OH)₂·8H₂O, NaCl, the composition II α-Fe₂O₃, δ-FeOOH, BaO₂·8H₂O, NaCl, and the composition III α-Fe2O₃, δ-FeOOH, BaO₂·8H₂O, NaCl. When calcined at 600°C, all the compositions contained the same ingredients, α-Fe₂O₃, BaO₂·8H₂O, NaCl, BaFe₁₂O₁₉. When calcined at 900°C, the compositions I and II gave hexagonal platelets of barium ferrite but the composition III did not. Also, the composition II, resulting in the hexagonal platelets of 0.1-0.5 μm in size, presented the highest values of saturation magnetization (σ_s), 71 emu/g, and intrinsic coercivity (_iHc), 5.3 kOe, since its particle size distribution before calcination was narrowest as well as smallest and thus attained the highest reactivity.

抄録全体を表示

  We, Hitachi Metals, have started the industrialization of Hard Ferrite in 1963 in Kumagaya Works. We have solved step by step the many difficult issues, like as raw materials, calcining, milling, pressing, sintering and grinding. We have succeeded the mass production for automobile motor segments by wet pressing and magnet rolls for electrostatic developing copy system by single press and magnetizing. These products have been become as actual standard system in the world. We have transferred the industrialized technology to over seas in the USA, Korea, Taiwan, Malaysia and India. The production amount in group total is now over 5,000 ton/month.

抄録全体を表示

  Magnetic properties of nanocomposite hard magnets consisting of Fe₃B and Nd₂Fe₁₄B have been modified in a wide range by adding an appropriate amount of Cr in the alloy produced by means of a rapid solidification technique. Powder of these materials is suitable for isotropic bonded-magnet applications with some advantages over conventional Nd₂Fe₁₄B melt-spun magnets with respect to magnetizability and high Br values. High-coercivity material, Nd_5.5Fe₆₆Cr₅Co₅B_18.5 with an intrinsic coercivity of 610 kA/m and a maximum energy product of 51kJ/m³, as obtained on compaction-molded magnets, shows greater stability at elevated temperatures compared to melt-spun Nd₂Fe₁₄B type materials. Reversible recoil behavior of magnetization is another unique characteristic of the Fe₃B-based nanocomposites. The range of demagnetizing field in which the magnets show reversible recoil of magnetization is expanded by Cr-doping. Enhancement of the stability against irreversible rotation of magnetization due to Cr-doping may be attributed to stabilizing effects on Fe₃B in which Cr partitions.

抄録全体を表示