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Magnetics, IEEE Transactions on

Issue 5 • Date Sept. 1989

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Displaying Results 1 - 25 of 363
  • Comments on "Minimizing power dissipation in a disk file actuator" by E.S. Cooper

    Publication Year: 1989 , Page(s): 4353 - 4354
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (146 KB)  

    The seek control problem that arises in the abovementioned work (see ibid., vol.24, p.2081-91, 1988) is formulated as an optimal control problem with constraints relating directly to specified design limits on input magnitude and power dissipation. The resulting control is optimal for a given peak-to-average power ratio. Power-optimal control and time-optimal control are special cases of this type of control.<> View full abstract»

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  • Magneto-resistance, stress effects, and a self-similar expansion model for the magnetization process in amorphous wires

    Publication Year: 1989 , Page(s): 3620 - 3622
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    The outer shell magnetization process was investigated from the point of view of its effects on longitudinal and transverse magnetoresistance (MR), magnetization, and domain structure observations as well as their stress effects for a Fe77.5Si7.5B 15 amorphous wire with a diameter of 125 μm prepared by rapid quenching in rotating water. The unusual behavior of the initial negative slope observed in the longitudinal MR is explained in terms of a realistic domain structure. A self-similar expansion model is proposed to explain the dynamical response of such a structure under applied fields and/or tensile stresses. It is suggested that the zig-zag domains of the outer shell are stabilized by a square closure domain which expands uniformly while maintaining a self-similar shape up to a threshold field of about 20 Oe and then deforms towards the saturation magnetization. However, this domain structure was destroyed or much deformed by a tensile stress along the wire axis of about 170 MPa in the sample. Such a critical stress depends on the diameter, quenching conditions, alloy composition, etc. This behavior and stabilization of the zig-zag domain by the closure domains give a novel mechanism for the magnetization processes which follow the re-entrant reversal, and are thus useful for the understanding of re-entrant reversal phenomena themselves View full abstract»

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  • Stability of one dimensional steady state domain wall motion

    Publication Year: 1989 , Page(s): 3854 - 3856
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The magnetization configuration and stability limits of one-dimensional domain walls with orthorhombic anisotropy and an applied field normal to the wall are studied in steady-state motion. The calculations are carried out directly on the directional sphere in the lossless instance. The Walker breakdown mechanism, in which the motion breaks down simultaneously along the entire wall profile, is replaced by three distinct mechanisms: domain instability in which the wall motion breaks down asymptotically far from the center of the wall, and two types of domain-wall instability in which the breakdown occurs within the wall. The two types of domain-wall instability are distinct in that only one is identified by Jacobi equation analysis View full abstract»

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  • Magnetostriction measurements for amorphous wires

    Publication Year: 1989 , Page(s): 3623 - 3625
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    Novel accurate and stable measurement methods for the magnetostriction constant λs and the induced anisotropy constant Ku are presented for amorphous wires. The two constants are theoretically expressed using a magnetization rotation model with or without tensile and compressive stresses. Values of flux densities Bs, B r, and Bm are estimated, observing 60 Hz BH characteristics of the amorphous wire to which a compressive stress is applied in order to realize the magnetization rotation behavior. Measured variations of λs and Ku of wires of different compositions for heat treatments with or without stresses are given. A figure of merit for stress sensor constitution is proposed as λsB s/Ku, a maximum value of which is obtained due to a compressive stress anneal for Fe-rich wires View full abstract»

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  • Effects of applied field inhomogeneities on the magnetization reversal of elongated γ-Fe2O3 particles

    Publication Year: 1989 , Page(s): 3662 - 3664
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    A detailed micromagnetic study of the effects of nonuniform applied fields in elongated particles is given. As a representative case the magnetization reversal is studied in the presence of a recording head field. The investigation is restricted to an important subproblem: the single particle in an inhomogeneous applied field. This case is also interesting with regard to the development of ultrahigh-density recording systems. Reversible and irreversible magnetization processes are computed for the limit of small and large exchange coupling. Results are presented for both longitudinal and perpendicular media View full abstract»

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  • Structure and magnetic properties of Nd2(Fe1-xCox)14B1-y Cy alloys

    Publication Year: 1989 , Page(s): 3298 - 3299
    Cited by:  Patents (1)
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    The reorientation temperature and magnetocrystalline anisotropy field (Ha) of Nd2(Fe1-xCox)14B1-y Cy in the temperature range 200-450 K were determined by AC initial susceptibility measurements and the singular point detection technique, respectively. The temperature dependence of saturation magnetization was measured on finely powdered polycrystalline samples in an extraction magnetometer in fields up to 80 kOe. It was found that the Nd2(Fe1-xCox)14 C (X⩽0.4) series consisted of a mixture of two phases, Nd2(Fe,Co)17Cx and α-(Fe,Co), irrespective of heat treatment schedules. Partial substitution of C for boron led to a slight increase of Ha, whereas substitution of Co for Fe (at low Co concentration) causes an increase of Ha at low temperature. Although the concentration dependence of Ms is reminiscent of the Slater-Pauling curve, no maximum was found at either 1.5 K or 300 K, as one would expect in Fe-Co and Nd2(Fe,Co)14B alloys View full abstract»

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  • Formation of magnetic grating on steel plates by electron/laser beam irradiation

    Publication Year: 1989 , Page(s): 3830 - 3832
    Cited by:  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The steels examined were a ferromagnetic carbon steel, S35C (equivalent to AISI 1035), and a nonmagnetic austenitic stainless steel, SUS 304 (equivalent to AISI 304). The gratings formed were magnetized in a 5.4-kOe field and the profile of the vertical component of magnetic flux leakage from each magnetized grating was measured. Changes of microstructure and mechanical strength of the beam-irradiated portions of the steel plates were also investigated. The measurements of the leakage flux profiles revealed the existence of remanent magnetism in the gratings. Metallographic and mechanical-hardness examinations showed that the original mixed ferrite/pearlite phase in the S35C steel was changed to martensite by beam irradiation. This increased its mechanical hardness. It was also determined that small grains of the ferrimagnetic ferrite phase were precipitated in the base of the nonmagnetic austenitic phase in the SUS 304 View full abstract»

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  • A study on magnetization model for particulate media

    Publication Year: 1989 , Page(s): 3665 - 3667
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    The leakage magnetic field of a single γ-Fe2O3 particle is observed by electron holography to be approximately single domain and uniaxial. On the basis of this result, a vector magnetization model is introduced in which curling and rotation in unison modes for a prolate take place. Using this model and the particle size and orientation distributions in γ-Fe2O3 particulate media observed by high-resolution scanning electron microscopy, M-H loops and Hc-Ω characteristics of the film are calculated. Moreover, read/write simulations of the isolated pulses are performed using the finite element method. These calculated results agree fairly well with measurements View full abstract»

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  • The influence of rare earth (RE) constituents on the magnetic and optical properties of RE-FeCo thin films

    Publication Year: 1989 , Page(s): 3746 - 3748
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The polar Kerr effect and perpendicular anisotropy of various rare-earth (RE)-FeCo films were measured and were found to have different dependencies upon the RE composition of the films. The polar Kerr effect was found to be largest for those films where Gd dominated the RE composition. Also, the polar Kerr effect was seen to decrease monotonically as increasingly heavy RE elements from Gd to Er dominated the RE composition. The other RE elements in this range are Tb, Dy, and Ho. In contrast, the perpendicular anisotropy of the same films was seen to be largest when Tb dominated the RE composition. The perpendicular anisotropy decreased rapidly when Gd was substituted for Tb and decreased gradually when increasingly heavy RE elements were substituted for Tb. It is also shown that the dependence of the Curie temperature upon RE composition for these RE-FeCo films correlates strongly with the dependence of the Curie temperature upon composition for pure RE alloys over a similar range of elements View full abstract»

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  • MR vector sensor with trimmable sense axis direction

    Publication Year: 1989 , Page(s): 3836 - 3838
    Cited by:  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    Magnetoresistive bridge sensors fabricated from thin-film Permalloy elements are biased by mutually opposing fields on adjacent arms of the bridge using integral thin-film bias magnets. The sensors have excellent vector response and good linearity in applied fields up to 1.5 Oe. It is shown both theoretically and experimentally that the axis of peak sensitivity is not aligned with any geometric edge of the sensor pattern but can be adjusted by varying the bias field. This ability to trim the sense-axis direction is discussed in relation to the production of three-axis sensor systems View full abstract»

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  • Recorded magnetizations and magnetic fields in media derived by computer simulation

    Publication Year: 1989 , Page(s): 3668 - 3670
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    The parameters of magnetic media dependences of the half pulse width, PW50, and output voltage of isolated pulse, E 0, were investigated using computer simulation. It was found that the squareness in the x direction (Sx) dependences of PW50 and E0 are different from the saturation magnetization dependences of PW50 and E 0 and that PW50 hardly changes with Sx for high S* (PW50Sx0.04), although it is proportional to Sx0.48 for low S *. The corresponding magnetization and the total magnetic field are also investigated for high Sx and low Sx media in three steps. These are the reversed write current, removed head, and reproducing process steps. It is confirmed that transition regions are formed mainly during the reversed write step View full abstract»

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  • Numerical modelization of transient current in relay

    Publication Year: 1989 , Page(s): 3593 - 3595
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    The authors describe the application of software for magnetic-field computation to the evaluation of transient current in the coil of a relay. The AZIMUT software package is used to compute the induced current in the coil and the electromagnetic force acting on the mobile part of the relay. This force is introduced in a simple mechanical equation to determine the change of position of the mobile part. The software has been modified to take into account the electromotive force induced by the movement. Some of the difficulties met in coupling the mechanical and electrical problems are discussed. The current measured in a relay fed with a voltage step is then compared to a computed curve. The shapes of the curves are similar. Several reasons for the differences between them are suggested View full abstract»

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  • A study on signal processing for enhanced density in vertical recording systems with MIG head

    Publication Year: 1989 , Page(s): 4087 - 4089
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    A waveform equalization technique is developed to enhance the recording density of a R/W (read/write) channel with a metal-in-gap (MIG) head and a CoCr single-layer medium. This equalization reduces the intersymbol interference of the reproduced pulse by eliminating the subpulse caused by the pseudogap of the MIG head and by transforming an asymmetric dipulse into a symmetric single pulse. By combining this equalizer with a head impedance equalizer and a write current equalizer, a high recording density channel of about 30 kfr/mm2 was attained View full abstract»

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  • Exchange coupled CoPd/TbCo magneto-optic storage films

    Publication Year: 1989 , Page(s): 3749 - 3751
    Cited by:  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    Films of CoPd with weak perpendicular anisotropy have been shown to exchange couple to square loop TbCo films on both the Tb and Co sides of compensation. The exchange is sensitive to reactive impurities at the interface and is broken under conditions that produce as little as one monolayer of paramagnetic compound. Even when the coupling at the interface is strong, it is shown that only a limited thickness of the CoPd layer is spin oriented perpendicular. It is noted that the CoPd system has some potential for applications in that it has a higher Faraday rotation than TbCo at short wavelengths of interest for higher-density storage systems View full abstract»

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  • Large Barkhausen jumps observed in Nd-Fe-B sintered magnets at very low temperatures

    Publication Year: 1989 , Page(s): 3431 - 3433
    Cited by:  Papers (1)
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    The demagnetization process for Nd15Fe77B 8 sintered magnets was studied by precise loop measurements below 50 K. A zigzag variation of coercivity with temperature was observed below about 18 K. In this temperature range, the magnetization reverses with large discontinuous magnetization jumps. The origin of the jumps, which are caused by the sudden growth of residual reversed magnetic domains pinned at some defects, was investigated by measuring hysteresis loops at very low temperatures and analyzing them from the viewpoint of domain-wall nucleation and propagation. The temperature of 18 K coincides with the Curie temperature of the B-rich Nd1.11Fe4B4 phase segregated in the Nd 15Fe77B8 magnet. This behavior may be related to the soft magnetic properties of the B-rich phase and the demagnetizing field in the magnet View full abstract»

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  • A Mossbauer study of CoMo-substituted barium ferrite

    Publication Year: 1989 , Page(s): 4069 - 4071
    Cited by:  Papers (1)
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    Well-resolved Mossbauer spectra were obtained for CoMo-doped barium ferrite with variable doping (0-33% Fe), heat-treatment temperature (825-1200°C), and sample temperature (90-300 K). Substitution was observed to occur primarily on the 12-K site, with little or no lattice distortion. A fitting model using five independent components, each a sextet, yielded the magnetic hyperfine field (ionic moment) of each site as a function of doping and sample temperature. A 10% reduction of the moment on the 2a site was observed upon doping, which results from its proximity to the 12-K site. Other sextet parameters were generally constant or followed monotonic trends View full abstract»

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  • Finite element analysis of 3D multiply connected eddy current problems

    Publication Year: 1989 , Page(s): 4009 - 4011
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    Three-dimensional eddy-current problems with multiply connected conductors are formulated in terms of uniquely defined potentials. In the eddy-current-carrying regions, a magnetic vector potential and an electric scalar potential are used. These are coupled to a magnetic scalar potential in most parts of the nonconducting domain. However, in the nonconducting `holes' in the conductors, a magnetic vector potential is used so that the region with the scalar description surrounds a simply connected domain. To ensure uniqueness of the vector potential, the Coulomb gauge is incorporated in the formulation and the normal component of the vector potential is set to zero on the interfaces between the vector-potential and scalar-potential regions. Solutions to two benchmark problems of the International TEAM Workshops involving multiply connected conductors are presented. The gain in computational time due to the use of unique potentials is pointed out View full abstract»

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  • Increased periodic magnetic fields for traveling wave tubes

    Publication Year: 1989 , Page(s): 3902 - 3903
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB)  

    The power output of a traveling-wave tube depends strongly on the strength of the axial magnetic field that guides its electron beam. Such fields are usually less than 5.0 kOe. With conventional permanent-magnet stacks, such fields are attainable only with periodic structures with periods of the order of the working bore diameters. The axial fields resulting from such structures have root-mean-square fields of about 3.5 kOe. The authors describe two novel stacks employing magic spheres that offer root-mean-square fields that are from two to three times as great, and that afford order-of-magnitude power increases over those of the conventional structures View full abstract»

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  • Switching mechanisms in cobalt-phosphorus thin films

    Publication Year: 1989 , Page(s): 3881 - 3883
    Cited by:  Papers (103)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    Studies have shown that although the interactions between grains in magnetic thin-film recording media can enhance the squareness, these interactions are also responsible for media noise. The authors made measurements on Co-P thin films that give a simple and practical way of investigating the role of interactions in the magnetic processes that occur in these films. All magnetic measurements were made on a PAR 155 vibrating sample magnetometer with a resolution of 10-5 EMU. The field measurements were made with a Bell-Gauss Hall probe calibrated with a proton magnetometer to give an accuracy of <0.1 Oe. The magnetic measurements made were the hysteresis loop. DC demagnetization, and isothermal remanent magnetization. It is noted that if a connection can be found between the results obtained and quantitative measures of noise in thin-film media, this work provides an important experimental link between models of the recording process and magnetic reversals in recording media View full abstract»

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  • Texture-induced magnetic anisotropy of Co-Pt films

    Publication Year: 1989 , Page(s): 3890 - 3892
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    The induced magnetic anisotropy of Co-Pt films on textured Ni-P-plated Al substrates depended on the Pt content of the films and texturing conditions. The axis of easy magnetization for the Co film was along the texture lines. The surface grains for an anisotropic Co-20at.%Pt film and those for an isotropic film with the same content seemed to have almost the same shapes, and no clear grain boundaries. No elongation of the grains or grain alignment normal to the grooves was observed. The remanent magnetization measured in the circumferential and radial directions was affected strongly by the Pt content, in a similar manner to magnetostriction View full abstract»

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  • Differentially DC biased type magnetic field sensor of high sensitivity

    Publication Year: 1989 , Page(s): 3396 - 3398
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    The detection principle of a novel magnetic field sensor called the differentially-DC-biased magnetic field sensor which uses a magnetic core is described. The detectable lower limit is extended up to the order of 10-13/√Hz by virtue of the detection principle used, which is analogous to the equilibrium condition of ordinary bridge circuits. By using two cores, a kind of bridge circuit is constituted. The field to be detected breaks the equilibrium condition, which leads to the variation of incremental permeability. The means adapted to detect the variation with high sensitivity are described View full abstract»

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  • Flux control and flux distribution in a ferrite orthogonal core

    Publication Year: 1989 , Page(s): 3839 - 3841
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    A graphical method is presented for obtaining the flux distribution in a ferrite core. This method can be applied to other types of orthogonal cores and can assist in quantitative analyses. The flux distributions are assigned to four classes on the basis of the flux pattern. The method of flux control and the resultant flux distribution in a ferrite orthogonal core are shown. It is demonstrated that the flux control characteristics can be analyzed by considering component fluxes View full abstract»

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  • CoZrRe amorphous film heads for high-density magnetic recording

    Publication Year: 1989 , Page(s): 3683 - 3685
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    CoZrRe amorphous film heads with superior performance have been developed for use in high-density magnetic recording. These films produce near-zero magnetostriction of less than +2.5×10-7 and saturation magnetization of 1.2 T. It is found that the addition of a small amount of Re to CoZr markedly improves the stability of magnetic properties during head fabrication. However, the process temperature must be less than 200°C. To realize the required temperature, a dry process is developed, using sputtered SiO2 films for insulation instead of conventional hard-cured photoresist. A maximum process temperature of about 150°C is obtained As a result, a high linear density of more than 2100 fr/mm (53 kfci) at a spacing of 0.1 μm is achieved using CoZrRe film heads and metal-sputtered media with a coercivity of 1300 Oe View full abstract»

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  • Results on `controlled polarity' modulation and coding

    Publication Year: 1989 , Page(s): 4090 - 4092
    Cited by:  Papers (2)  |  Patents (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    The authors present results on a controlled-polarity modulation/coding scheme. They review this scheme and describe how to choose certain code parameters for the purpose of comparing the controlled polarity scheme to conventional (d,k) coding with NRZI modulation. A computer simulation is then utilized to compare the different schemes in terms of effective signal-to-noise ratio (SNR) and peak shift. It is shown that the controlled polarity schemes have less peak shift than the conventional schemes, whereas the conventional schemes have a higher effective SNR. It appears that in systems with a high enough SNR, the loss in effective SNR could be outweighed by the decrease in average peak shift. This could be of particular interest in future systems using magnetoresistive heads which have the potential to yield substantially higher SNRs View full abstract»

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  • A direct-overwrite system for magneto-optical systems with a soft-magnetic shield

    Publication Year: 1989 , Page(s): 4036 - 4038
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    A direct overwrite system for magnetooptical storage systems is analysed which includes an extra field source in the form of a thin permanent magnetic film and a soft magnetic shield between the memory and field-source layers. Locally, the shielding power of the soft film can be canceled purposefully by raising the temperature above its Curie temperature by selecting an adequate power level of the write laser. Thus, the field of the extra field source can penetrate through the paramagnetic hole into the writeable region of the storage layer, and controls the magnetization direction in the latter. The groove structure in the disk surface is used to obtain fringing fields induced by the second field source outside this layer. A suitable structure of the film stack is analyzed by finite element calculations, which show that write fields can be obtained up to 2.5 kA/m. The development of the paramagnetic hole in the soft layer and its position with respect to the writeable region is studied as a function of the shape of the laser power, the physical parameters of the layers, and the disk velocity. It is concluded that a pulse frequency of about 10 MHz should be possible 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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Meet Our Editors

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