Showing papers on "Coercivity published in 1993"
TL;DR: Arrays of ferromagnetic nickel and cobalt nanowires have been fabricated by electrochemical deposition of the metals into templates with nanometer-sized pores prepared by nuclear track etching, displaying distinctive characteristics because of their one-dimensional microstructure.
Abstract: Arrays of ferromagnetic nickel and cobalt nanowires have been fabricated by electrochemical deposition of the metals into templates with nanometer-sized pores prepared by nuclear track etching. These systems display distinctive characteristics because of their one-dimensional microstructure. The preferred magnetization direction is perpendicular to the film plane. Enhanced coercivities as high as 680 oersteds and remnant magnetization up to 90 percent have also been observed.
1,146 citations
TL;DR: In this paper, a permanent magnet alloy based on Nd-Fe-B, which contains 8-9 at% Nd and processed by melt spinning, is described. But the magnetically hard Nd2Fe14B alloys consist of two phases, a matrix of magnetically-hard Nd 2Fe 14B with numerous particles of α-iron on grain boundaries.
458 citations
TL;DR: In this paper, the bcc-nanocrystalline Fe-M-B (M=Zr, Hf, and Nb) alloys produced by annealing a melt-spun amorphous phase were investigated in a ring shape form with the aim of clarifying the application potential as a core material.
Abstract: Magnetic core properties, core loss, permeability, and saturation magnetic induction of bcc‐nanocrystalline Fe–M–B (M=Zr, Hf, and Nb) alloys produced by annealing a melt‐spun amorphous phase were investigated in a ring‐shaped form with the aim of clarifying the application potential as a core material. The bcc alloys exhibit high saturation induction (Bs) from 1.49 to 1.63 T combined with high permeability (μe) from 22 000 to 32 000 at 1 kHz and 0.4 A/m. The bcc Fe–M–B (M=Zr, Hf, or Nb) alloys also show low core losses (W) from 1.4×10−1 to 2.1×10−1 W/kg at 50 Hz and 1.4 T and from 1.70 to 2.50 W/kg at 1 kHz and 1.0 T. The W values attained for the bcc Fe–M–B (M=Zr, Hf, and Nb) alloys are smaller by 60%– 90% at 50 Hz and 1.4 T and 50%–70% at 1 kHz and 1.0 T, as compared with those for an amorphous Fe78Si9B13 alloy in practical use as a transformer core material. The low W values for the bcc‐nanocrystalline alloys are presumably due to the small anomaly factor comparable to a Co‐based amorphous alloy. The c...
192 citations
TL;DR: The coercive field of a magnetically soft prismatic grain of irregular cross-section embedded in a hard magnetic matrix has been calculated as a function of the size of the soft magnetic grain this paper.
178 citations
TL;DR: In this article, a crystallization treatment of amorphous (Nd,Dy)xFe80.5−x−yCoyB18.5M1 alloys for 3≤x≤5 and 0≤y ≥5, where M represents the additives Al, Si, Cu, Ga, Ag, and Au. The results showed that adding Co and M results in a significant reduction of the crystal grain size and leads to significant improvements both in the intrinsic coercivity and in the energy product.
Abstract: High‐coercivity, high‐remanence permanent magnet materials have been obtained via a crystallization treatment of amorphous (Nd,Dy)xFe80.5−x−yCoyB18.5M1 alloys for 3≤x≤5 and 0≤y≤5, where M represent the additives Al, Si, Cu, Ga, Ag, and Au. It has been found that addition of Co and M results in a significant reduction of the crystal grain size and leads to significant improvements both in the intrinsic coercivity and in the energy product. The materials are superior to Nd2Fe14B‐based rapidly solidified materials in the remanence Br, the temperature coefficient of Br, and magnetizability. The typical values of temperature coefficients of Br and HcJ are, respectively, −0.05%/K and −0.35% K. The magnetizing force required to obtain substantial remanence is approximately 0.8 MA/m. Compaction‐molded resin‐bonded magnets produced from these materials have magnetic performance (Br, HcJ) in the range between 0.89 T, 0.29 MA/m and 0.80 T, 0.35 MA/m.
157 citations
TL;DR: The coercivity values for different heat-treated samples were found to be in the range 20−95 Oe, which are significantly larger than that for samples having grain sizes of the order of a few microns as mentioned in this paper.
154 citations
TL;DR: In this article, the substitution of Ga is found to play an important role in the stability of high carbon rare-earth iron compounds with 2:17-type structure, and a novel hard magnetic compound series with composition Sm2Fe14Ga3Cx (x=0, 0.5, 1.0, 1 5, 2.5) was prepared by arc melting.
Abstract: A novel hard magnetic compound series with composition Sm2Fe14Ga3Cx (x=0, 0.5, 1.0, 1.5, 2.0, and 2.5) was prepared by arc melting. The carbides crystallize in the rhombohedral Th2Zn17‐type structure and are single phase except for Sm2Fe14Ga3 and Sm2Fe14Ga3C0.5 which contain some amounts of α‐Fe. The substitution of Ga is found to play an important role in the stability of high carbon rare‐earth iron compounds with 2:17‐type structure. The Curie temperatures of Sm2Fe14Ga3Cx are 200–240 K higher than that of Sm2Fe17. All compounds with x=0–2.5 exhibit an easy c‐axis anisotropy at room temperature. The anisotropy fields increase with increasing carbon concentration from 70 kOe for x=0 to at least 90 kOe for x≥1.5. A room‐temperature coercivity of 15 kOe is obtained in Sm2Fe14Ga3C1.5 prepared by melt spinning at a speed of 30 m/s.
135 citations
TL;DR: In this paper, the phase formation and magnetic properties of Fe100−xCox powders were investigated with respect to phase diffraction and measurements of the saturation magnetization and the coercivity.
Abstract: Fe100−xCox and Fe100−xNix powders were prepared by mechanical alloying of the elements in a planetary ball mill. They were investigated with respect to phase formation and magnetic properties using x‐ray diffraction and measurements of the saturation magnetization and the coercivity. In both systems, disordered solid solutions were formed by mechanical alloying as proved especially by the measurement of the saturation magnetization. Moreover, nonequilibrium microstructures were established consisting in a nanocrystalline state (average minimum grain sizes 20–30 nm) accompanied by the introduction of considerable atomic‐level strain (root mean square strain up to 1%). The soft magnetic behavior of this material shows some features of rapidly quenched nanocrystalline ribbons, but very low coercivities are prevented by a predominant influence of strain via magnetoelastic interaction.
131 citations
TL;DR: In this article, nanoparticles of barium ferrite (BaFe 12 O 19 ) were synthesized using a novel method called microemulsion processing, where the aqueous cores of water-cetyltrimethylammonium bromide (n -butanol) octane microemulsions were used as constrained microreactors for the co-precipitation of precursor carbonates.
130 citations
TL;DR: Elongated ferromagnetic single-domain particles are believed to exhibit a high stability of their remanent magnetization but here it is shown that for elongated particles thermal fluctuations lower the coercivity much more drastically than predicted by current theories.
Abstract: Elongated ferromagnetic single-domain particles are believed to exhibit a high stability of their remanent magnetization However, here it is shown that for elongated particles thermal fluctuations lower the coercivity much more drastically than predicted by current theories The rate for magnetization reversal is calculated for a classical model of a ferromagnet that allows for a spatially nonuniform magnetization distribution along the sample The prefactor of the Arrhenius factor is explicitly evaluated and analytical results are obtained in the experimentally important limit of external magnetic fields close to the anisotropy field and for moderate damping
125 citations
TL;DR: In this paper, the static magnetic properties of three different doped barium ferrite compounds prepared by the glass crystallization method were studied and the dependence on temperature of the macroscopic magnetic parameters has been analyzed.
Abstract: We have studied the static magnetic properties of three different M‐type doped barium ferrite compounds prepared by the glass crystallization method. The zero‐field‐cooled (ZFC) and field‐cooled (FC) processes have been recorded at low field and they all show the typical features of a small particle system. The ZFC curves display a broad peak at a temperature TM, which depends on the distribution of particle volumes in the sample. Isothermal magnetization curves M(H) at several temperatures and saturation magnetization Ms as a function of temperature have been measured for the Co‐Ti sample (BaFe10.4Co0.8Ti0.8O19). The dependence on temperature of the macroscopic magnetic parameters has been analyzed. The distribution of blocking temperatures is studied from the derivative of the remanent‐to‐saturation magnetization ratio with respect to temperature and it is fitted to a lognormal distribution, leading to a mean blocking temperature 〈TB〉=(81±40) K. The distribution of volumes of the magnetic unit is also o...
TL;DR: In this article, the modified coprecipitation method has been shown to be suitable for preparing BaFe2y−2χCoχTiχO19 powder with narrow particle size distribution (50-80 nm).
TL;DR: In this article, Ba and Sr ferrites are prepared by sol-gel technique with different Fe/Ba(Sr) ratios in the starting materials, and magnetization, coercive, and anisotropy field strength are determined depending on the heat treatment of the gel and the iron/barium(strontium) ratio.
Abstract: Ba and Sr ferrites are prepared by sol‐gel technique with different Fe/Ba(Sr) ratios in the starting materials. Magnetization, coercive, and anisotropy field strength are determined depending on the heat treatment of the gel and the iron/barium(strontium) ratio in the starting material. A two‐step heat treatment is used to prepare single‐domain powders with high magnetization. These powders prepared by sol‐gel technique show single‐domain behavior with specific magnetization σS=649 A cm2/g and coercive field strength HcM=402 kA/m in the case of Ba ferrite and σS=695 A cm2/g and HcM=416 kA/m for Sr the ferrite. Al‐substituted ferrites with high anisotropy field strengths are prepared additionally. Ferromagnetic resonance absorption is used to determine the anisotropy field strength and to investigate the formation process of the hexaferrite phase during the heat treatment. The beginning of hexaferrite formation occurs at annealing temperatures below 700 °C.
IBM1
TL;DR: In this paper, the authors review the recent advances made toward the attainment of high areal density in the Gb/in/sup 2/2/4/1 regime.
Abstract: The authors review the recent advances made toward the attainment of high areal density in the Gb/in/sup 2/ regime. they review recent progress made in understanding the relationship between the media magnetic properties and recording characteristics such as linear resolution, transition noise, and overwrite. For high-linear-resolution media, a coercivity in the 2000-3000-Oe regime is now attainable, depending on the alloy, underlayer, and other process parameters such as substrate temperature bias. Various noise reduction schemes have been developed in recent years which are based on the decoupling of exchange interactions between magnetic grains or between multiple magnetic layers. As the bit cell size is further reduced in the Gb/in/sup 2/ regime, one of the main challenges will be to retain a high coercivity with decreasing grain size of the magnetic film. >
TL;DR: In this article, high coercivity, c-axis randomly in-plane oriented barium hexaferrite thin films have been successfully fabricated by using conventional rf diode sputtering and postdeposition annealing.
Abstract: High coercivity, c‐axis randomly in‐plane oriented barium hexaferrite thin films have been successfully fabricated by using conventional rf diode sputtering and post‐deposition annealing. Coercivities as high as 4100 Oe have been achieved. Ms, Sq, S*, SFD, and SFDr reach the values of about 270 emu/cc, 0.63, 0.90, 0.12, and 0.084, respectively. CoTi doping not only reduces the coercivity, but also reduces the grain size and improves the c‐axis in‐plane orientation. The composition of doped films can be controlled through different diffusion processes. In this way coercivities in a range between several hundred oersteds and 4000 Oe can be easily obtained.
TL;DR: In this paper, the magnetic properties of ultrafine amorphous Fe 1- x C x particles have been studied as a function of temperature and applied field, and the mean particle diameter of the Fe-C particles in the present study was about 3.1 nm.
Patent•
02 Apr 1993
TL;DR: In this article, a first magnetic layer 11, a second magnetic layer 12, a third magnetic layer 13 and a fourth magnetic layer 14 are successively laminated and the magnetic walls 15 are moved backward by heating TS.
Abstract: PURPOSE:To greatly improve a recording density and transfer speed and to miniaturize the reproducing device by enabling the reproduction of signals of periods below the diffraction threshold of light at a high speed without lowering the amplitude of the reproduced signals. CONSTITUTION:A first magnetic layer 11, a second magnetic layer 12 and a third magnetic layer 13 are successively laminated. This first magnetic layer 11 is relatively smaller in the coercive force of magnetic walls than the third magnetic layer and is larger in the mobility of the magnetic walls. The second magnetic layer 12 is lower in Curie temp. than the first magnetic layer and the third magnetic layer. Further, a fourth magnetic layer may be formed between the first magnetic layer and the second magnetic layer. The magnetic walls 15 are moved backward by heating TS.
TL;DR: In this paper, the magnetomechanical hysteresis model of Sablik and Jiles is extended to treat magnetic properties in the case of noncoaxial stress and magnetic field in an isotropic, polycrystalline medium.
Abstract: Although descriptions of the effect of stress on spontaneous magnetization within a single domain already exist, there remains no adequate mathematical model for the effects of noncoaxial magnetic field and stress on bulk magnetization in a multidomained specimen. This article addresses the problem and provides a phenomenological theory that applies to the case of bulk isotropic materials. The magnetomechanical hysteresis model of Sablik and Jiles is thus extended to treat magnetic properties in the case of noncoaxial stress and magnetic field in an isotropic, polycrystalline medium. In the modeling, noncollinearity between magnetization and magnetic field is taken into account. The effect of roll‐axis anisotropy is also considered. Both magnetic and magnetostrictive hysteresis are describable by the extended model. Emphasis in this article is on describing properties like coercivity, remanence, hysteresis loss, maximum flux density, and maximum differential permeability as a function of stress for various angular orientations between field and stress axis. The model predictions are compared with experimental results.
TL;DR: In this article, the thickness dependence of the perpendicular magnetic anisotropy, coercivity, nucleation field and remanence in an ultrathin Co wedge (0-9 monolayers) grown epitaxially on Pt(111) and capped by a thin Pt overlayer has been investigated using magneto-optical Kerr effect.
Abstract: We have used the magneto‐optical Kerr effect to study the thickness dependence of the perpendicular magnetic anisotropy,coercivity,nucleation field and remanence in an ultrathin Co wedge (0–9 monolayers)grown epitaxially on Pt(111) and capped by a thin Pt overlayer. In addition, the spin‐reversal mechanism in the Co layers has been investigated using Kerr domain imaging. The sample showed perpendicular magnetization up to an extrapolated Co thickness of 15 monolayers (ML), with derived volume and interface anisotropy constants of −0.77 MJ/m3 and 1.15 mJ/m2, respectively. The Kerr rotation and Kerr ellipticity demonstrated linear dependences on the Co thickness (t Co), with sizeable extrapolated offsets at t Co=0, attributed to polarization of the Pt by the Co. The coercivity (H c ) and nucleation field both rose to peak values at t Co=1.5 ML, with a subsequent monotonic fall‐off for higher Co thicknesses. In the case of H c , this fall‐off did not demonstrate the t Co −5/2 dependence shown by a similar Pd(111)/Co/Pd sample investigated earlier.
TL;DR: In this paper, the effects of experimental deformation on the magnetic properties of a set of synthetic calcite sandstone samples containing magnetite were quantified in a microcomputer-controlled apparatus that adjusted the applied differential stress as needed to maintain a constant strain rate of 10−5 s−1.
Abstract: We have quantified effects of experimental deformation on the magnetic properties of a set of synthetic “calcite sandstone” samples containing magnetite. The deformation was carried out in a microcomputer-controlled apparatus that adjusted the applied differential stress as needed to maintain a constant strain rate of 10−5 s−1. Most samples were deformed under dry conditions, but a few were deformed with a pore fluid present; the samples deformed under dry conditions required substantially higher differential stresses. Macroscopically ductile shortening strains of up to 25% produced the following irreversible changes in magnetic properties: (1) increased bulk coercivity, remanence coercivity, and mean anhysteretic remanence susceptibility; (2) decreased mean low-field susceptibility; (3) decreases in the component of remanence parallel to shortening; (4) smaller decreases for most samples in the component normal to shortening, resulting in a net “rotation” of the remanence away from the shortening axis; (5) larger decreases in the normal component in a few samples, resulting in a net “rotation” of the remanence towards the shortening axis; (6) increased magnetic anisotropy; and (7) increased “deformation” of initial magnetic ellipsoids. A comparison of data for samples deformed under dry and wet conditions (higher and lower differential stresses, respectively) indicates that remanence reorientation and susceptibility anisotropy are controlled primarily by bulk strain (i.e., rotation and displacement of particles), whereas coercivity and anhysteretic anisotropy are controlled dominantly by microstrain or intragranular stress.
TL;DR: A systematic magnetic study is carried out on samples at diferent decomposition states in order to determine the process of transformation into the stable phases, observing a 20% maximum diminution on the magnetic moment with increasing temperatures of the thermal treatment.
Abstract: A ferromagnetic and supersaturated fcc Fe_51Cu_49 solid solution has been obtained by mechanical alloying. After subsequent thermal treatments the fcc phase undergoes a spinodal decomposition which finally, at 780 K, yields a mixture of fcc and bcc phases. In this work, a systematic magnetic study is carried out on samples at diferent decomposition states in order to determine the process of transformation into the stable phases. We observe a 20% maximum diminution on the magnetic moment with increasing temperatures of the thermal treatment. The Mossbauer spectrum taken at 8 K shows that 20% of the Fe atoms are in a nonferromagnetic state. On the other hand, upon heating up to 723 K the roomtemperature coercive field increases dramatically to 640 Oe, and after cooling down to 10 K it decreases to 270 Oe. Deviations from the T law in the temperature dependence of the magnetization have been observed. This behavior is explained by fluctuations in composition due to the spinodal decomposition, which lead to fluctuations of the magnetic order parameters, i.e., magnetic moment and Curie temperature.
TL;DR: The key observation is a nonthermal character of the relaxation below a few kelvin, which is in agreement with theoretical suggestions on quantum tunneling of magnetization.
Abstract: We present a comprehensive study of the low-temperature magnetic relaxation in random magnets. The first part of the paper contains theoretical analysis of the expected features of the relaxation, based upon current theories of quantum tunneling of magnetization. Models of tunneling, dissipation, the crossover from the thermal to the quantum regime, and the effect of barrier distribution on the relaxation rate are discussed. It is argued that relaxation-type experiments are ideally suited for the observation of magnetic tunneling, since they automatically provide the condition of very low barriers. The second part of the paper contains experimental results on transition-metal\char21{}rare-earth amorphous magnets. Structural and magnetic characterization of materials is presented. The temperature and field dependence of the magnetic relaxation is studied. Our key observation is a nonthermal character of the relaxation below a few kelvin. The observed features are in agreement with theoretical suggestions on quantum tunneling of magnetization.
TL;DR: In this paper, a high performance and inexpensive hysteresis loop tracer was developed to measure quasistatic (0.02 Hz or less) loops of soft ferromagnetic materials.
Abstract: A high‐performance and inexpensive hysteresis loop tracer has been developed to measure quasistatic (0.02 Hz or less) hysteresis loops of soft ferromagnetic materials. It was applied very successfully to measure straight pieces of amorphous and nanocrystalline ribbons and amorphous wires. Especially high‐magnetic‐field resolution is required when nanocrystalline ferromagnets and amorphous wires are measured. Nanocrystalline materials exhibit very low coercivity (Hc=0.1–0.5 A/m). The error of Hc measurement using this tracer does not exceed 0.05 A/m even though the amorphous wires have very small cross section (0.008 mm2). The examples of hysteresis loops measured at low (50 A/m) and high magnetic field (14 kA/m) are presented. The apparatus consists of an IBM‐compatible computer equipped with 12 bit analog‐to‐digital and digital‐to‐analog converters, bipolar power supply, fluxmeter, solenoid and a pickup coil connected to a compensation coil. This equipment is free of 50 Hz noise, a significant problem in...
TL;DR: In this paper, the microstructure and magnetic properties of polycrystalline Fe films with thicknesses of 200-1000 A have been investigated, and the films were prepared by rf sputtering onto SiO2 substrates.
Abstract: The microstructure and magnetic properties of polycrystalline Fe films with thicknesses of 200–1000 A have been investigated. The films were prepared by rf sputtering onto SiO2 substrates. The investigation was prompted by the lack of data on sputtered Fe films in this thickness regime as well as disagreement in the data for evaporated films. In addition to thickness, substrate temperature and deposition pressure were varied to examine their effect on the microstructure. The film microstructure was characterized by x‐ray diffraction, transmission electron microscopy, and Auger spectroscopy. The polycrystalline films did not display a strong preferred orientation and had average grain sizes of 60–85 A. Surface oxide layers formed upon exposure to air ranged from 10 to 80 A, the thicker oxides formed on films with lower density. Magnetic hysteresis measurements were made with a vibrating sample magnetometer. Below 1000 A, porosity and surface oxidation result in reductions up to 25% in the saturation magnet...
TL;DR: Barium ferrite particulates have been prepared by coprecipitation and calcination in a flux of NaCl-KCl, and it was found that a flux containing more than 30 wt% KCl tends to seriously deteriorate the magnetic properties of resultant perticulates as mentioned in this paper.
TL;DR: In this article, a comprehensive study of the magnetic properties of noninteracting single-domain particles with cubic magnetocrystalline anisotropy is presented, where numerical calculations extend the zero-temperature predictions of Joffe and Heuberger and enable the effects of thermally activated magnetization reversal on the hysteresis loop at finite temperatures.
Abstract: A comprehensive study of the magnetic properties of non-interacting single-domain particles with cubic magnetocrystalline anisotropy is presented. These numerical calculations extend the zero-temperature predictions of Joffe and Heuberger and enable the effects of thermally activated magnetization reversal on the hysteresis loop at finite temperatures to be determined. Variations in particle size distribution are also considered. Calculations indicate a reduction in the intrinsic coercivity as the mean particle diameter is reduced and an increase in coercivity for small particle diameter systems as the standard deviation of the size distribution is increased.
TL;DR: In this article, BaTiO3 films on Pt substrates were fabricated by electrophoretic deposition method by using fine powder (0.1 µm in diameter) with fine powder consisting of BaTi3, acetone and iodine, which were formed in an applied DC field of 500 V/cm.
Abstract: BaTiO3 thick films on Pt substrates were fabricated by the electrophoretic deposition method. The suspension was prepared with fine powder (0.1 µm in diameter) of BaTiO3, acetone and iodine. Dense and strong films were formed in an applied DC field of 500 V/cm. The films sintered at 1200°C were crystallized into the tetragonal phase at room temperature. The coercive field Ec and the remanent polarization Pr were estimated to be 1.6 kV/cm and 2.1 µC/cm2, respectively, from the P-E hysteresis loop observation.
TL;DR: In this article, the effects of ferroelectric switching on dielectric and electric properties in lead zirconate titanate ceramics are investigated. And the experimental results are modeled and explained by the phenomenological principles and atomistic mechanisms for the participation of domain walls and bulk polarization in on-shelf aging, ac field deaging, and Ferroelectric fatigue effects.
Abstract: Effects of ferroelectric switching on dielectric and ferroelectric properties in lead zirconate titanate ceramics are investigated. Ferroelectric switching induces rejuvenation of weak field dielectric constant, K, and ferroelectric polarization, P, initially through the ac field deaging effect, and then induces accelerated decrease in K and P through the ferroelectric fatigue effect. ‘‘On shelf’’ aging of K, ferroelectric switching induced decrease of K, ac field deaging induced augmentation in K and P, and ferroelectric polarization fatigue are illustrated and intercompared. The experimental results are modeled and explained by the phenomenological principles and atomistic mechanisms for the participation of domain walls and bulk polarization in on shelf aging, ac field deaging, and ferroelectric fatigue effects.
TL;DR: In this article, a finite element formulation of the micromagnetic problem is used to minimize the total magnetic Gibbs free energy of interacting magnetic particles in the framework of an adaptive mesh refinement scheme.