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Magnetics, IEEE Transactions on

Issue 5 • Date September 1987

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Displaying Results 1 - 25 of 574
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Chariman's preface

    Page(s): 2036
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    Freely Available from IEEE
  • Magnetic anisotropy of Co-Cr thin films as a function of substrate temperature during deposition

    Page(s): 2037 - 2039
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    A sequence of Co78Cr22films, 500 nm in thickness, was prepared by deposition on glass in a modified Varian D.C. magnetron S-gun sputtering system. The substrate temperature during deposition, Ts, was fixed at various values with an upper limit of 300°C. Specimens were examined by VSM, TM, FMR and TEM. Msrises significantly with increasing Ts, peaking at 200°C at 370 emu/cm3. The effective volume-averaged anisotropy drops for Ts>110°C from +1.6 KOe to progressively negative values (-4.3 KOe at 300°C). From FMR we find indications of the presence, in addition to the transition and bulk layers, of a highly negative anisotropy constituent (sim-11.5KOe anisotropy field). This resonance appears at Tsvalues of 150°C and above. TEM plane and cross-section views taken on a Ts= 150°C specimen show islands composed of tilted columns within the bulk. For vertical recording, specimens prepared at Tsvalues between 50 and 100°C are recommended. On the other hand, for longitudinal recording applications, films prepared at Tsvalues above 250°C would seem to be appropriate. View full abstract»

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  • Deposition rate dependence of coercivity in vaccum evaporated CoCr films

    Page(s): 2040 - 2042
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    Deposition rate dependence of perpendicular coercivity Hcl in Cocr evaporated films at the deposition rate ranging from 0.4nm/s to 400nm/s is studied. Hcl increases with decreasing deposition rate as well as with increasing substrate temperature. A High Hcl over 500 Oe, which has ever been obtained only at a substrate temperature over 250°C when deposition rate is high(400nm/s), is obtained at a substrate temperature of 150°C under deposition rate of 2nm/s. "Shoulder" in the hysteresis loop disappears as Hcl exceeds 400 Oe. Therefore to decrease the deposition rate and to increase the substrate temperature have the same effect on Hcl. Saturation magnetization of the films with the same Cr concentration increases with decreasing deposition rate, and it is suggested that the degree of Cr segregation increases with decreasing deposition rate. Hcl is independent of the background pressure when the relative pressure, the quotient of (background pressure/deposition rate), is between 2×10-8and 5×10-6torr/(nm/s). From the results above, it is clarified that the difference of deposition rate between vacuum evaporation and sputtering is one of the major reasons for the difference of Hcl between the two. View full abstract»

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  • The effects of incident angle on C-axis orientation in sputtered Co-Cr films

    Page(s): 2043 - 2045
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    The effects of the incident angle of the sputtered atoms on the crystallographic orientation in the Co-Cr films have been investigated in detail. Specimen films 1000 - 2000 Å thick were prepared by the Facing Targets Sputtering (FTS) system. The specially designed mask was used for collecting only the sputtered particles with the quasi-coherent incidence to the substrate. When the films are prepared at relatively low argon gas pressures, the effect of incident angle is not so apparent and the well c-axis oriented films can be obtained for the incident angle below 45°. This result indicate that the surface diffusion may be dominant over the incident angle for attaining the desired crystallographic orientation in the films when they are prepared at low working gas pressures. Owing to the unique target/substrate layout, the plasma-free FTS system with low working gas pressures may have much larger flexibilities for preparing the well c-axis oriented Co-Cr films as compared with the conventional sputtering systems or the vacuum evaporation one. View full abstract»

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  • Inclining columnar structure in Co-Cr films prepared by roll magnetron sputtering

    Page(s): 2046 - 2048
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    Co-Cr films, sputtered onto continuously transported substrates, exhibit columnar structure bowing according to incident angle variation during deposition. Surface grains were found to be elongated along the substrate moving direction. This factor seems to be related with the relative film motion. The column inclination is well approximated by the incident angle of the atom beam vector sum, considering the incidence probability from the two line target sources. It was found, by analysing the surface grain shapes using a high speed image processor, that the Co-Cr grains exhibited a sharp normal probability distribution in regard to diameter. View full abstract»

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  • CoCr-sputtering in large scale roll coating systems

    Page(s): 2049 - 2051
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    CoCr-layers have been DC-magnetron sputtered onto Polyimide web in a 2 side sputter roll coater for 1.2 m web width. Magnetic as well as crystallographic properties have been investigated as function of the deposition parameters: layer thickness, coating drum temperature, background pressure and angle of incidence. First measurements of electro-magnetic properties also have been made. The influence of different protective layers on the lifetime of a CoCr floppy disk has been checked in first experiments. View full abstract»

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  • The shearing of perpendicular loop with columnar structure

    Page(s): 2052 - 2054
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    The experimental results on the hysteresis loops of magnetic films with perpendicular anisotropy show that the loop is sheared. The shearing of the loops depends strongly on the thickness of the film. This phenomenon was never successfully explained with the particulate model. We use a simple three dimensional particulate model with an effective demagnetizing field to calculate the slope of the perpendicular loops. The calculated results are compared with the experimental results for the CoCr sputtered films. By considering different separation distance of the columns, good agreement is obtained between the calculations and the experimental data for the shearing of the loop. View full abstract»

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  • Domain studies of CoCr with perpendicular anisotropy

    Page(s): 2055 - 2057
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    R.F. Magnetron sputtered CoCr films (79/21 at%) with various thicknesses are magnetically characterized. The domain structure is observed by digitally enhanced Kerr microscopy and depends on the Hc/Hk values of the samples. For low and high coercivity films a comparison is made between the measured VSM hysteresis, domain period and a theoretical domain model. The domain shape is a function of the magnetic history of the sample and the bending created by the deposition process. View full abstract»

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  • Magnetic properties and microstructure of sputtered Co-Cr films

    Page(s): 2058 - 2060
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    Microscopic structural parameters of sputter-deposited Co-Cr films, such as the effective crystallite size along the thickness direction Deff(=coherent length), the strain < ε2>1/2, and the lattice spacing d00.2have been systematically studied by means of X-ray analysis and transmission electron microscopy (TEM) in conjunction with the magnetic properties. Cross-sectional observations by TEM revealed that a number of slip bands exist in the poorly oriented films. Slip and deformation bands interrupt the coherency along the c-axis in films, giving a spread to the orientation of the c-axis across the band boundaries. The effective crystallite size Defffor such poorly oriented films was found to be less than 200 Å, which is consistent with the period of contrast observed by TEM. When a film was annealed, Deffwas found to increase and the saturation magnetization Ms decreased, implying that Cr segregation as well as slip bands decreased throughout the thickness. View full abstract»

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  • Segregation in sputtered Co-Cr films

    Page(s): 2061 - 2063
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    The segregation growth process in sputtered Co-Cr films is investigated by examining the effect of substrate temperature on the segregated microstructure and magnetic properties. In sputtered Co-25at%Cr films, segregation occurs below 560°C, and both the saturation magnetization and the perpendicular anisotropy constant show a maximum around a substrate temperature of 300°C, where a specific microstructure, called a CP (chrysanthemum-like pattern) structure, is observed. The results suggest that the CP structure becomes observable in the highly segregated state and generates high perpendicular anisotropy. A new segregation growth model is derived from the results of the CP structure observations. Using this model, it is possible to explain the continuous transition of the magnetization mode between the continuous and the particulate modes. View full abstract»

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  • Dependence of segregated microstructure in sputter-deposited CoCr film on deposition conditions

    Page(s): 2064 - 2066
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    The compositional segregation of sputter-deposited CoCr films prepared under substrate temperatures Ts of 90-160°C and Ar gas pressures PAr of 4-30 mTorr are studied by transmission electron microscopy. The segregated microstructure depends on Ts and PAr. The degree of the segregation increases as Ts increases, and is maximized at a medium PAr. Saturation magnetization increases as the degree of the segregation increases. Vertical coercivity in film with the same degree of the c-axis orientation increases as the degree of segregation increases. View full abstract»

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  • Effect of addition of carbon on magnetic properties of sputter-deposited CoCr film

    Page(s): 2067 - 2069
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    The addition of carbon changes Ms, Hkeff and Hc(perp) of sputter-deposited CoCr films: Ms is always increased, while Hkeff and Hc(perp) are either increased or decreased by the addition of up to 0.32 at% carbon. How the substrate temperature and the Cr content in the film influence the effect of added carbon is investigated. Higher substrate temperature tends to stimulate the increase in Ms caused by the addition of carbon. A higher substrate temperature and higher Cr content tend to stimulate the increase in Hkeff and Hc(perp) and to prevent the decrease in Hkeff and Hc(perp) caused by the addition of carbon. The increase in Ms with the addition of carbon seems to be caused by an increase in the degree of compositional segregation. The increase and decrease in Hkeff may be attributed to an increase and decrease in Ku, respectively. The increase in Hc(perp) caused by the addition of carbon is probably due to the increase in Ku and/or to the refinement of the magnetic domain. The decrease in Hc(perp) may be attributed to the decrease in Ku even though the magnetic domain is refined. View full abstract»

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  • Extremely high bit density recording with single-pole perpendicular head

    Page(s): 2070 - 2072
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    Since perpendicular magnetic recording is free from recording demagnetization, high-density recording up to the intrinsic limit of a recording medium is possible. This prediction was verified experimentally in a flexible disk system using a single-pole head and a Co-Cr/Ni-Fe double-layer medium. We could record and reproduce signals up to 680KFRPI. The recording bit length at the highest density was of the order of the Co-Cr columnar diameter. View full abstract»

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  • Measurement of intensity of recorded magnetization on Co-Cr film by electron holography

    Page(s): 2073 - 2075
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    Electron holography has excellent features that permit the direct observation of magnetic flux in micro regions and the quantitative measurement of the flux intensity. Using this method, the intensity of recorded magnetization on a Co-cr single layer medium is measured. As a result, it is revealed that the demagnetization factor, which is determined by the aspect ratio of the recorded bit cell, dominates the magnetization recorded in contact with a head. It is also learned that the spacing loss in the recording process is -160d/λ[dB). View full abstract»

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  • Peak shift characteristics for barium ferrite flexible disk drive

    Page(s): 2076 - 2078
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    Output waveform and peak shift characteristics for low squareness Ba-ferrite perpendicular recording flexible disk (FD), the same as used for 3.5 inch Ba-ferrite 4MB FDD, were investigated by both calculation and measurement. A simple simulation for an isolated pulse and density responses was carried out and an estimation method for the perpendicular component factor, Kp, was derived. The peak shift characteristics and Kp for a Ba-ferrite FD were investigated for various recording /reproducing conditions, such as head gap length, recording current, etc. Then, it is shown that both the Kp value and peak shift are not so large, and therefore a phase equalizer is not needed for the low squareness Ba-ferrite FD. View full abstract»

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  • Nonlinear superposition in saturation recording of disk media

    Page(s): 2079 - 2081
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    The magnetic readback signal is generally assumed to be made up of linearly superposed single transition responses. As the transition spacing is reduced, this property is seen not to hold, With particulate disks, we find the head signal can be reconstructed as a linear superposition of variably spaced individual transitions, while with cobalt alloy film disks, both the spacing and the amplitude of individual transitions vary as a function of the data. This behavior is interpreted by a self consistent 2D recording model, linear superposition improves dramatically with lowM_{r}tdisk media. View full abstract»

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  • Pulse distortion in transitions recorded with thin film pole tips

    Page(s): 2082 - 2084
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    The transitions recorded on particulate, longitudinal media by a thin film ring head can exhibit a distortion at high write currents that adds an oscillatory structure to the density response and also degrades the amplitude at high density. The main data transition is recorded at the trailing edge of the gap, while the distortion is a second pulse written at the edges of the data track by the trailing edge of the trailing pole tip and at the expense of the transition recorded by the gap. This produces two pulses of opposite polarity with a constant peak-to-peak amplitude, separated by a distance equal to the thickness of the trailing pole tip and with the distortion appearing as a spurious pulse ahead of the data pulse. View full abstract»

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  • Comparison of the magnetic recording performance of medium-scale ring, double-sided pole, metal-in-gap heads on high-coercivity longitudinal media

    Page(s): 2085 - 2087
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    The magnetic recording performance of medium-scale ring, double-sided pole, and metal-in-gap (MIG) heads were investigated on standard longitudinal high-coercivity floppy, video tape, and isotropic floppy media using a stretched-surface multi-head magnetic recording tester. The isolated pulses for the ring and MIG heads exhibited sharp peaks near tbe edges of the gap for a head-medium separation of less than 0.1 um. Low density maximum output voltage was independent of the type of the write head. The largest output voltage was achieved from the MIG head. The isolated outputs on video media agreed with calculated values for the ring head efficiency set to 52% and the pole head efficiency set to 33% using the Karlqvist head field approximation. View full abstract»

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  • A measurement of signal-to-noise ratio versus trackwidth from 128 µm to 4 µm

    Page(s): 2088 - 2090
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    Bulk-erased tape noise will vary as the square root of the reproduce head trackwidth if the noise signal is uncorrelated across the track. Recent models of erased noise involve clusters of interacting particles that could be as large as a few microns. As the trackwidth (TW) approaches the cluster size, the noise should become correlated across the track and the tape-noise-limited signal-to-noise ratio (SNR) should become constant as TW is further reduced. A check of this idea using inductive heads is impractical. Magnetoresistive (MR) heads have very high signal and low noise and so are well suited for this task, but precautions must be taken to minimize thermal and Barkhausen noise. A multichannel MR head having TW from 128 μM to 4 μM was built to explore the areal reproduce density limits of MR heads and measure the bulk-erased SNR versus TW for 3M 5198 tape. Tape-noise-limited performance was achieved with the narrowest 4μM TW channel at a wavelength as short as 1μM. A wideband-equalized SNR of 20 dB was demonstrated with this channel at a wavelength of 1.27 μm or 40 kilo flux changes per inch (40 kFCI), at a tape speed of 38.2 cm/sec. With a 100% guard band, or an 8-μm track-to-track pitch, this corresponds to the very high areal storage density of 127 MFC/in2. The SNR was found to vary assqrt{TW}down to TW = 4 μm, which indicates that the expected particle cluster size must be smaller than 4 μm in the crosstrack direction. View full abstract»

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  • Noise of low-coercivity single-layer perpendicular recording media

    Page(s): 2091 - 2093
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    The noise of single layer CoCr media is investigated. A model is developed by treating the medium as a collection of columns. It appears that there is a strong correlation between magnetization direction of the columns. Neighbouring columns tend to have the same magnetization polarity, indicating exchange interaction. It is concluded that the media consist of domains. The domain width increases with the medium thickness. These domains can also result in a poor signal response at short wavelength. View full abstract»

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  • Permanent magnets based on 4f-3d compounds

    Page(s): 2094 - 2099
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    This paper briefly traces the 20-year development history of the magnets that are based on intermetallic compounds of rare-earth and iron-group transition metals. Some fundamental properties that make the 4f-3d alloys useful for permanent magnets are reviewed. The wide variety of practical magnet types, methods for their production and some economic aspects are discussed. Prospects for further development and improvement of these magnets are analyzed in terms of various application requirements. View full abstract»

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  • Metallographic study on Nd-Fe-Co-B sintered magnets

    Page(s): 2100 - 2102
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    Metallographic study has been carried out on the Nd-Fe-Co-B alloys to clarify the change in coercivity with the Co composition substituted for Fe in the Nd2Fe14B type sintered magnets. The decrease in coercivity caused by the Co substitution is attributed to the formation of soft-magnetic phases such as Nd(Fe, Co)2and Nd(Fe, Co)3. The mole ratio of Nd to (Fe+Co) of these soft-magnetic phases decreases with increasing the Co substitution. The Co concentration is much higher in these soft-magnetic phases than in Nd2(Fe, Co)14B matrix. The A1 addition in Nd-Fe-Co-B magnet makes the Nd(Fe, Co)2compound unstable to form the non-magnetic Nd3(Fe, Co, Al) compound, resulting in the increase in the coercivity of Nd-Fe-Co-B magnet. View full abstract»

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  • Precipitation in NdFeB-type magnet materials

    Page(s): 2103 - 2105
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    The microstructure of sintered magnets and melt-spun samples made from Nb-containing (Nd,Dy)FeB material has been investigated using transmission and scanning electron microscopy, X-ray microanalysis and thermogravimetric analysis. Comparison of the sintered specimens with NdDyFeB and NdFeB magnets revealed the existence of two additional phases. One of these is an Fe2Nb Laves compound. The second additional phase takes the form of small Nb-containing coherent precipitates within the main Nd2Fe14B grains. In the sintered magnet these particles ranged in size from 20-50 nm. Melt-spun ribbon contained a dispersion of smaller inclusions, typically 5-10 nm in diameter. The presence of these precipitates may be related to the enhanced coercivity found in the magnet and melt-spun samples. View full abstract»

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  • On the role of the ND-rich phases in sintered ND-FE-B magnets

    Page(s): 2106 - 2108
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    Sintered Nd15-Fe77-B8 magnets contain a multiphase microstructure. Our analytical transmission electron microscope study reveals that the Nd-rich phase, which is an essential part of the liquid phase sintering process can be divided into at least 4 subtypes with different Nd:Fe-ratios. Impurities of the raw material such as Nd-oxides and Nd-chlorides are randomly found in magnets, partly in the form of small inclusions up to 500 nm diameter within 2:14:1-hard-magnetic grains and partly in the form of large grains up to several microns diameter. As consequence of this analytical study a high concentration of boron vacancies as well as iron vacancies, especially in grain boundary regions is proposed. We have found that the degree of continuity of the intergranular Nd-rich phase is proportional to the intrinsic coercivity of the magnet. The intrinsic coercivity of sintered Nd-Fe-B magnets is determined by the nucleation of reversed domains and by the expansion of the reversed muclei, which is hindered by the non-magnetic Nd-rich oxide grain boundary layer phase. 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