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Magnetics, IEEE Transactions on

Issue 2  Part 1-2 • Date Mar 1994

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Displaying Results 1 - 25 of 290
  • Preparation of magnetic nanoparticles (γ-Fe2O3) in the silica matrix

    Publication Year: 1994 , Page(s): 821 - 823
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    Nanoparticles γ-Fe2O3 were prepared in silica matrix by the sol-gel process. Conventional acid hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) were used for the preparation of porous silica matrix. Iron(III) nitrate was homogeneously dissolved in the initial TEOS solution. After gelification and drying, the xerogel was heat treated on the air at different temperature between 700-900°C. The heating products were studied by high resolution TEM and magnetic measurements. Monocrystalline nanoparticles of γ-Fe 2O3 of size ranging between 50-100 Å were observed by HR TEM in the sample heated at 900°C. Room temperature magnetic measurements show a weak ferrimagnetic component for samples heated until 880°C, but a ferrimagnetic behaviour is evident at 4 K. The samples heated at higher temperature show ferrimagnetic behaviour at room temperature View full abstract»

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  • Effects of interstitials on the transition metal sublattice anisotropy in YFe10.5Mo1.5Zx(Z=H, N; x≈1)

    Publication Year: 1994 , Page(s): 684 - 686
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The effects of interstitial atoms in rare earth (R) intermetallic compounds are: strong increase in Curie temperature, weak increase of saturation magnetization and large influence in the crystalline electric field (CEF) at the R atom. These effects are more remarkable in carbide and nitride compounds than in hydrides. In this paper we will show that additional effects concerning the transition metals (T) occur. In YFe10.5Mo1.5, with ThMn12-type structure, it is shown that the introduction of H or N leads, also to an increase of both the Curie temperature and Fe moment. The most remarkable effect is that whereas with hydrogen we observe an increase of the easy c-axis anisotropy, with nitrogen the anisotropy becomes easy plane. View full abstract»

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  • Thin film heads for digital multi-channel recorder

    Publication Year: 1994 , Page(s): 243 - 249
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    The fabrication and performance of thin film magnetic heads newly developed for a digital multi-channel recorder are described. The reproducing head is a yoke type magnetoresistive head and the recording head is an inductive head. Four kinds of noise peculiar to the yoke type magnetoresistive heads have been completely suppressed by strict control of process conditions. Two new processes for a coil and a core have been applied to the recording head. Two reproducing heads and one recording head are assembled in a tape guide block ensuring accurate tape transport and stable tape-to-head contact. The characteristics of both the reproducing head and the recording head have proved to be sufficient for a digital multichannel recorder View full abstract»

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  • The role of a critical distance in RMn2 compounds

    Publication Year: 1994 , Page(s): 837 - 839
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    In the RMn2 system, the antiferromagnetically ordered Mn moments are reported to disappear at a reduction of the Mn-Mn distance, either by applying external pressure or by alloying. We illustrate the phenomena for the hexagonal NdMn2 compound. The Neel temperature in the (Nd,Lu)Mn2 system is found to vanish; at substitution of 30% of Nd by Lu, considered to be equivalent-to applying a pressure of 24.5 kbar. Antiferromagnetic order of the Mn sublattice, however, vanishes already at substitution of 7% of Mn by Cu and of 3% of Mn by Fe in the NdMn2, being equivalent to an external pressure of only 4 kbar. High-pressure studies on the Nd(Mn,Cu)2 system show that the effect of an external pressure on the Neel temperature decreases markedly with increasing Cu concentration, in contrast to what is expected in a critical distance model View full abstract»

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  • A simple but efficient iteration algorithm for self-consistent magnetic recording models

    Publication Year: 1994 , Page(s): 250 - 252
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    This paper describes a simple and easy to implement algorithm for carrying out iterative self-consistent calculations of the magnetic recording problem. This algorithm does not require the choice of any “relaxation parameter” yet will rapidly converge to a solution for any problem in which the recording medium is characterized by a continuous hysteresis loop model. Simulation results comparing this algorithm with optimal “fixed relaxation parameter” performance is given View full abstract»

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  • Brillouin light scattering studies of Co/GaAs(001) films

    Publication Year: 1994 , Page(s): 769 - 771
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    Thermal magnetic excitations in epitaxial Co films deposited on GaAs(001) surfaces have been studied at room temperature using Brillouin light scattering. The films have thicknesses in the range 3 to 20 nm. The variations of MSSW frequency with applied field at constant wavevector and the variation of MSSW frequency with wavevector at constant field have enabled the magnetizations and anisotropy fields to be determined. The variation of MSSW frequency as the films were rotated about the incident light axis enabled the form of the anisotropy to be determined View full abstract»

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  • 5th European Magnetic Materials and Applications Conference (EMMA '93)

    Publication Year: 1994
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (904 KB)  

    The following topics were dealt with: amorphous and nanocrystalline magnetic materials; permanent magnets; magnetic thin films, multilayers, surfaces and fine particles; magnetization processes; soft magnetic materials; materials for electrical applications; magnetic sensors; magnetooptic materials and recording; magnetic semiconductors; magnetic insulators and microwave applications; magnetic anisotropy and magnetostriction; magnetic measurement; field calculations; technology of strong magnetic fields and high pressures; ferrofluids; molecular magnetism; magnetic polymers and biomagnetism; strongly correlated systems; high temperature superconductor; heavy fermions; fluctuating valence and Kondo systems View full abstract»

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  • Correlation between saturation magnetostriction and saturation polarisation in Fe-Pt-B amorphous alloys

    Publication Year: 1994 , Page(s): 516 - 517
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    The concentration dependence of saturation magnetostriction and saturation polarisation for amorphous Fe85-xPtxB 15 (x=0, 1, 3, 5) alloys were measured at room temperature. It was found that saturation magnetostriction in the series of glassy alloys increases with increasing Pt content. We suggest that this behaviour is connected with the perturbation of the Fe-B glassy matrix by the Pt atoms. The polarisation versus temperature scans support an exceptional role of Pt in the Fe-Pt-B amorphous alloy, too View full abstract»

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  • Antiferromagnetic planar-rotator model. Extension to next-nearest interaction

    Publication Year: 1994 , Page(s): 1084 - 1086
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    The mean-field analysis of the antiferromagnetic planar (XY) model on square lattice with the nearest- and second-nearest neighbour interaction without and under magnetic field is carried out. A number of phase transitions are observed, both of the first- and second-order and also multicritical points are present in the system View full abstract»

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  • Magnetic viscosity of uniform γ-Fe2O3 particles with different degrees of cationic ordering

    Publication Year: 1994 , Page(s): 772 - 774
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    Results are presented about the time dependence of the magnetization in γ-Fe2O3 particles obtained from α-Fe2O3 through a reduction-oxidation process. The precursor particles were prepared by homogeneous hydrolysis in solution. This preparation method led to a narrow distribution of particle dimensions which allowed us to consider the particles as being monodisperse. The viscosity study included the evaluation of the activation volume of pressed powder samples formed by spindle-like γ-Fe2O3 particles (aspect ratio 6) with different degree of order in their cationic distribution, at temperatures from 100 to 480 K View full abstract»

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  • Allicat magnetoresistive head design and performance

    Publication Year: 1994 , Page(s): 298 - 302
    Cited by:  Papers (10)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    The general design features of the magnetoresistive (MR) merged head are described and compared to the earlier MR piggy-back head called Corsair. Examples of static, magnetic and error rate testing are given. Dual track profiles show the read-narrow feature of the MR head. Stability of the signal with write disturbance shows the effectiveness of the hard-bias longitudinal biasing. Error rate vs. off-track position indicates the robustness of the file design View full abstract»

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  • High frequency head and playback model for thin-film recording heads

    Publication Year: 1994 , Page(s): 394 - 403
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    A thin-film head field and readback model that allows for eddy currents has been proposed and used to compute complex head efficiency, inductance, anomalous (ac) resistance, head saturation fields and locations, as well as the digital playback parametrics high and low frequency amplitude, resolution, PW-50, and maximum overwrite fields with a fair amount of accuracy. The head model solves for the time-dependent vector potential in a geometry that closely resembles a modern three dimensional thin-film recording head, including variable pole and yoke width, thickness, permeability, resistivity, neck angle and other geometrical parameters. Readback emulation is done with a discrete Fourier version of the reciprocity integral using Szczech fields and arctan transitions, along with complex efficiencies from the head model. Detailed comparisons with experimental observations are given View full abstract»

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  • Optimization of magnet end-winding geometry

    Publication Year: 1994 , Page(s): 162 - 167
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    A simple, almost entirely analytic, method for the optimization of stress-reduced magnet-end winding paths for ribbon-like superconducting cable is presented. This technique is based on characterization of these paths as developable surfaces, i.e., surfaces whose intrinsic geometry is flat. The method is applicable to winding mandrels of arbitrary geometry. Computational searches for optimal winding paths are easily implemented via the technique. Its application to the end configuration of cylindrical Superconducting Super-Collider (SSC)-type magnets is discussed. The method may be useful for other engineering problems involving the placement of thin sheets of material View full abstract»

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  • Magnetic phase transitions in R2Fe17 compounds under pressure

    Publication Year: 1994 , Page(s): 619 - 621
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    The effect of the pressure up to 1.4 GPa on the Curie temperature Tc in the R2Fe17 intermetallics with R=Nd, Er and Y was measured using a low field susceptibility technique. The identical character of the temperature dependence of susceptibility X(T) of the R2Pe17 intermetallics observed at ambient pressure (sharp step-like drop at Tc) is preserved at high pressures only in the case of Nd2Fe17. Pronounced broadening and splitting of the sharp drop of X(T) was observed in Er2Fe17 and Y2Fe17 respectively. The initial pressure slopes of dTc/dp are large and negative for all studied compounds, having nearly the same values (dTc/dp=-36K/GPa for Nd2Fe17 compound). Our results are discussed from the point of view of the sensitivity of Tc on the crystal structure, the number of nearest neighbours of Fe atoms and the possible effect of “disordered” structures in the R2Fe17 intermetallics View full abstract»

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  • High field magnetization of single crystalline Ho2Co17 under pressure

    Publication Year: 1994 , Page(s): 1087 - 1089
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    High-field magnetization measurements up to 38 T have been performed on a-newly-grown single-crystalline Ho2Co17 sample along the main crystallographic directions of the hexagonal cell. The magnetization curve along the easy direction (b-axis) exhibits a metamagnetic-like transition at 23.6 T whereas for the a-axis a similar transition occurs at 32.4 T. The transitions are extremely sharp-much sharper than in previously grown crystals. The transitions are understood as a moment-flip transition associated with the formation of a noncollinear magnetic structure in this ferrimagnetic compound. From the transition-field value the 3d-4f spin-exchange parameter has been derived. Magnetization under pressure up to 5 kbar has been used to determine the pressure dependence of the magnetic transition at 23.6T. The pressure dependence dBtr/dP amounts to -24 TMbar-1 View full abstract»

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  • Spin=1/2 XY magnetic ordering of Nd3+ ions in NdGaO3

    Publication Year: 1994 , Page(s): 960 - 962
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    Heat capacity of the perovskite NdGaO3 has been measured in the range of 0.15 K<T<3 K showing an anomaly that is interpreted as ordering of the Nd3+ ions at Tc=0.97±0.01 K. This is, to our knowledge, the best example of a 3D XY magnetic ordering in a rare earth system, free from any other contribution, and the first such example of a Nd compound View full abstract»

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  • Magnetic interactions in giant magnetoresistive Co-Ag heterogeneous films

    Publication Year: 1994 , Page(s): 726 - 728
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    The effect of the micromagnetic configuration on the giant magnetoresistance of a metastable cobalt-silver thin film prepared by sputtering is investigated. The difference between the magnetoresistance immediately after cooling in zero field and after field cycling is interpreted by invoking interactions between the active magnetic regions in the sample View full abstract»

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  • High areal density recording using an MR/inductive head and pre-embossed rigid magnetic disk

    Publication Year: 1994 , Page(s): 404 - 409
    Cited by:  Papers (1)  |  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    To determine whether a newly developed PERM (Pre-Embossed Rigid Magnetic) disk can be used with an MB/inductive head and a PRML (Partial-Response Maximum-Likelihood) channel, an experimental digital magnetic recording system was developed. This system used an external clocking scheme instead of a conventional self-clocking scheme. The track pitch was 5.2 μm, and the track width was 3.6 μm. Basic read-write characteristics, such as signal-to-noise ratio, frequency response, positive/negative symmetry or the readback pulse, were measured. An areal density of 605 kbit/mm2 (390 Mbit/inch2) was obtained at a bit error rate of 10-6 View full abstract»

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  • Homogenisation behaviour of Nd2(Fe0.98Nb0.02)14B alloy

    Publication Year: 1994 , Page(s): 616 - 618
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    The effects of the homogenisation conditions on the microstructure of a Nd2(Fe0.98Nb0.02)14B alloy have been investigated. In the as cast condition the microstructure of the alloy contains four phases, the Nd2Fe 14B matrix phase, a Nb-containing ternary phase (Nb26 Fe32B42), Nd-rich regions and free iron. In contrast, the homogenised alloy contains only the first two phases and very small amounts of the Nd-rich phase. The Nb26Fe32 B42 ternary phase was found to originate (nucleate) in the heart of the free iron phase which provides strong evidence for the role of Nb in the removal of free iron from the microstructure. The electrical resistivity of the alloy was measured at regular intervals during the homogenisation process at 1000°C and these studies revealed that, after 40 hours, the alloy was completely homogenised and this was in a good agreement with the microstructural studies. The resistance measurements also indicated a degree of anisotropy in the as-cast material and there was a maximum in resistance at an intermediate stage which could indicate an age hardening process. The resistance was found to correspond to a microhardness value View full abstract»

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  • Three-dimensional magnetic ordering in Bi2CuO4

    Publication Year: 1994 , Page(s): 1163 - 1165
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    The heat capacity of Bi2CuO4 has been measured from 5 to 350 K in an adiabatic calorimeter. A long range ordering peak was found at 42.7 K due to the establishment of three-dimensional antiferromagnetic order. The magnetic entropy calculated for the anomaly corresponds to the theoretical value for spin 1/2, ΔS=Rln2, discarding the existence of any lower dimensional magnetic contribution at a higher temperature View full abstract»

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  • Magnetic and magnetoelastic properties of amorphous ribbons

    Publication Year: 1994 , Page(s): 518 - 520
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB)  

    A phenomenological model for the magnetic and magnetoelastic behaviour of the field-annealed magnetostrictive ribbon is proposed. The basic hypothesis is that the magnetic domain coupling energy due to the inhomogeneity inherent to amorphous state is dependent on the reduced magnetization. The model takes into account the anisotropy energy, Zeeman energy, magnetoelastic energy and magnetic domain coupling energy. The magnetization, engineering magnetostriction and Young's modulus are derived as continuous functions of the applied magnetic field and stress View full abstract»

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  • An optimal design of capacitor-driven coilgun

    Publication Year: 1994 , Page(s): 207 - 211
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    The paper presents an analysis and optimal design of a capacitor-driven inductive coilgun. An equivalent circuit is used for a launch simulation of the coilgun. The circuit equations are solved together with the equation of motion of the projectile by using the Runge-Kutta method. The numerical results are compared with the experimental values to verify the usefulness of the developed simulation program. It is shown that the numerical and the experimental results are in a good agreement. In the design of the system optimization is achieved by employing the genetic algorithm. The resultant specifications of the coilgun optimally designed by the proposed algorithm are tested by experiment. Finally the obtained results are compared with those designed by approximate equations and by linear search methods as well. It is found that the proposed algorithm gives a better result in the energy efficiency of the system, namely it enables one to obtain a higher muzzle velocity of the projectile with the same amount of energy View full abstract»

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  • Giant magnetoresistance and antiferromagnetically coupled Co fraction in Co/Cu multilayers with varying number of periods

    Publication Year: 1994 , Page(s): 809 - 811
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    The giant magnetoresistive signal of Co/Cu multilayers as a function of the number NCo of Co layers is experimentally investigated for Cu thicknesses of 1 nm, i.e. in the 1st antiferromagnetic maximum, and for Co layer thickness of 1 nm. The stacks were deposited by DC magnetron sputtering on an Fe buffer. The fraction FAF of the film that couples antiferromagnetically is derived from the hysteresis curves. A correction of FAF is required for the buffer and one Co layer. The FAF of stack periods close to the buffer is about 1, while FAF reduces at large stack thicknesses. The GMR of stacks with small thicknesses is limited by the diffuse scattering at the outer surfaces. The GMR of thicker stacks depends on FAF and the resistivity. Furthermore, the meaning of FAF is discussed. By optimizing N Co, we achieved Δρ/ρ's as high as 72% at room temperature View full abstract»

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  • Theory of a dynamical coercive force in magnets with microscopic defects

    Publication Year: 1994 , Page(s): 824 - 827
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    The peculiar dynamical drag force Fc can arise at the domain wall motion in a magnet with microscopic defects, such that it cannot pin the domain wall in the usual way. The value of Fc is finite as the domain wall velocity v goes to zero. The reason for such behavior is the emission of bending waves of the domain wall. The calculations for different types of impurities as well as for both bulk ferromagnet and ultrathin magnetic layers are presented. In 3D ferromagnet the Fc value is finite at v→0 and this is interpreted as the dynamical coercive force. In the 2D case (e.g. in monolayer films) the drag force diverges at small velocities as Fc ∝1/v1/2. In the film with a finite thickness and very small v the force has a viscous character: Fc∝v View full abstract»

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  • Heat and moisture diffusion in magnetic tape packs

    Publication Year: 1994 , Page(s): 237 - 242
    Cited by:  Patents (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    The purpose of this paper is to present theory and experiments on heat and moisture diffusion in magnetic tape packs. The theory includes anisotropy effects. The same fundamental mathematical theory is applied to heat and moisture diffusion. The tape packs have been submitted to a variety of thermal and hygroscopic conditions. By fitting experimental curves, a heat diffusivity coefficient of 1.8·10-7 m 2/s was obtained for the radial direction. Separate experiments showed that the heat diffusivity in the axial direction is about twice the value in the radial direction. For the radial moisture diffusivity coefficient, a literature value of 4·10-13 m2/s is used. Fitting experimental curves then shows that the axial diffusion is about 300 to 500 times that of the radial diffusion, which indicates that most of the moisture enters through the faces of the pack. Finally, it is shown that the experimental pack boundaries are not at a fixed temperature. Heat diffusion experiments in a stirred water bath best approximate the constant temperature requirement, and theoretical fits to those experimental curves have been most satisfactory View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology