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Magnetics, IEEE Transactions on

Issue 6 • Date Nov 1988

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Displaying Results 1 - 25 of 296
  • High density magneto-optical recording using 0.67 μm band high power laser diode

    Publication Year: 1988 , Page(s): 2300 - 2304
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    High-density optical recording on a magnetooptical disk has been achieved by a compact optical head that uses a 0.67-μm-band high-power visible-light laser diode. The recording density has been improved to 1.5 times that for conventional optical recording, using a 0.83-μm laser diode, as a result of the increase in linear density and track density. The C/N ratio for the readout signal is greater than 50 dB View full abstract»

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  • Domain observation and its compositional dependence in RE-TM magneto-optical media

    Publication Year: 1988 , Page(s): 2305 - 2307
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    Recording domains in magnetooptical media were observed with a polarizing microscope. Regularly shaped domains were observed for transition-metal-rich compositions, whereas jagged domains were observed for rare-earth-rich compositions with compensation temperatures close to the Curie temperature. The results were interpreted by means of a force-balance model. The dependence of the domain size and shape on the external magnetic field is discussed View full abstract»

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  • Thermomagnetically written domains in TbFeCo thin films

    Publication Year: 1988 , Page(s): 2308 - 2310
    Cited by:  Papers (1)
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    Characteristic features of thermomagnetically written domains in amorphous Tbx(Fe90Co10)100-x thin films having different magnetic properties are reported. In particular, the writing process in materials with low Tb content (x⩽21), which is dominated by the demagnetizing field, is compared to the bias-field-dominated process in Tb-rich samples (22⩽x⩽25). Domain-wall movement over lateral dimensions of the bit size is found for Tb-poor materials, while for x⩽22 the domain boundaries are primarily determined by the area heated up to the Curie temperature. The importance of mechanical stress in domain formation and irreversible changes of the storage medium due to overheating in the writing process are reported View full abstract»

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  • Observation of domain expansion and contraction in TbFe films by Lorentz microscopy

    Publication Year: 1988 , Page(s): 2311 - 2313
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    Lorentz electron microscopy techniques have been used to study in situ, at room temperature, the expansion and contraction of thermomagnetically written circular domains in Tb19Fe81 and Tb32Fe68 films. Domains expand or contract more or less radially in Tb19Fe81, but with the development of jagged walls. In Tb32Fe68, dendritelike stripe domains with jagged walls form either outside or within the existing domains, leaving the perimeter of the initial circular domains unchanged. The difference in behavior can be understood in terms of the difference in the importance of the local demagnetizing field relative to the local total field. The implications of the nonuniform wall motion for the appearance of domain irregularity during thermomagnetic recording are discussed View full abstract»

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  • A system for measurement of domain wall motion in amorphous rare earth-transition metal alloys

    Publication Year: 1988 , Page(s): 2314 - 2316
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    A system has been developed for measuring domain-wall motion in amorphous rare-earth-transition-metal alloys. A one-dimensional scanning technique is utilized in which a focused, oscillating HeNe laser spot moves over the magnetization pattern in the film. Domain walls are detected through the polar Kerr effect as the spot scans the film. A magnetic field is applied to the film in order to move the domain walls. The maximum line-scanning rate is about 250 Hz. The spot diameter at a 632.8-nm wavelength is limited to about 8 μm by the 0.46 numerical aperture of the focusing objective, the beam waist of the laser, and aberrations. The domain wall position can be measured to within ±1 μm. The apparatus is described, and the results domain-wall-motion measurements are presented View full abstract»

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  • The role of the compensation temperature in thermomagnetic switching

    Publication Year: 1988 , Page(s): 2317 - 2319
    Cited by:  Papers (1)
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    Amorphous rare-earth-transition-metal alloys with different compensation temperatures, Tcomp, exhibit pronounced differences in the temperature characteristics of the coercivity in the high-temperature range. This is of primary importance for the thermomagnetic switching process in which the domain radius, domain regularity, or domain jitter must be controlled. The influence of the coercivity profile on these parameters has been investigated for alloys with Tcomp>100 K. The radial dependences of the driving fields acting on the domain wall are calculated using experimental data for the saturation magnetization, uniaxial anisotropy, and coercivity View full abstract»

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  • Numerical simulation of recorded bit in magneto-optical media having thermally different protective layers

    Publication Year: 1988 , Page(s): 2320 - 2322
    Cited by:  Papers (2)
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    The influence of the thermal properties of the media in a multilayered magnetooptical disk on thermomagnetic recording characteristics such as recorded bit size and sensitivity has been investigated. Thermal properties have been simulated using several different dielectrics and metals for both undercoat and overcoat layers. Media with oxide layers represent those having low thermal diffusivity and large heat capacity, whereas nitride layers represent those with high thermal diffusivity and small heat capacity. Small domains are formed when an Al layer covers a Ta2O5 overcoat. Both recording sensitivity and bit-size increase for media with nitride layers compared with those having an Al top coat. When the same recording power is applied, media with oxide layers provide the most sensitive disks with the largest recorded bit-size among the structures studied. The results are explained by the differences in the heat capacities of the media together with the differences between the vertical and lateral heat flow throughout the layered structure View full abstract»

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  • Spot and mark-size characterization in magneto-optic recording

    Publication Year: 1988 , Page(s): 2323 - 2325
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    The attainable performance of a magnetooptic (MO) recording system is determined by the laser intensity profile and the size and shape of the written magnetic domain. The authors present a computer model that provides MO readout waveforms based on an overlap integral of the scanning laser spot and the written domains. This model and regression analysis are applied to experimental magnetooptic readout waveforms, and the laser profile and mark size are determined. A nonlinear least-squares fit of readout data yields a unique determination of the laser-spot profile and written-domain size. The effects of groove width and thermal blooming on domain shape can be included in the modeling. The results are compared to those of other spot and domain measurements, and close agreement is obtained View full abstract»

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  • Demagnetizing field computation for dynamic simulation of the magnetization reversal process

    Publication Year: 1988 , Page(s): 2326 - 2328
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The magnetic-field distribution for a thin magnetic film is computed using the fast Fourier transform technique. The method is quite general and accommodates any two-dimensional magnetization distribution. It allows the computation of fields both inside the film (demagnetizing fields) and outside (stray fields and leakage) View full abstract»

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  • Possibilities of perpendicular magnetic recording

    Publication Year: 1988 , Page(s): 2329 - 2334
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    The potential of perpendicular magnetic recording using a single-pole head and a double-layered medium has been investigated theoretically by computer analysis and compared with that of longitudinal magnetic recording. In conventional longitudinal recording, a recording demagnetizing loss due to the change of magnetization mode from semicircular to circular shapes occurs with increasing recording level at high bit density. In perpendicular magnetic recording, the perpendicular magnetization mode is maintained regardless of recording level even at an extremely high bit density of 571 kFRPI. This indicates that the perpendicular recording medium has a very high recording resolution, where a single bit size approaches several diameters of the microcrystalline particles of the Co-Cr layer. An ultrahigh density at which the recording area for 1 bit will reach 1 μ2 at present and 500 Å2 in future should be possible View full abstract»

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  • The origins of defects in sputtered Co-Cr perpendicular magnetic recording media

    Publication Year: 1988 , Page(s): 2335 - 2337
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    The authors examine various causes of contamination and the defects they produce, and they typify some defects that originate at the metal/substrate interface, as nodules or extraordinary particles. They find that these are not caused by dirt or mishandling, but are induced by an exudate from the polymide substrates used. The nodules' characteristic acorn shape can be analyzed mathematically to suggest a possible exudate-induced mechanism for their formation and growth. The authors conclude that most of these defects can be eliminated View full abstract»

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  • High bit density (100 Mb/cm2) with single-layer Co-Cr media and ring heads in perpendicular magnetic recording

    Publication Year: 1988 , Page(s): 2338 - 2340
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    The signal and noise of single-layer Co79Cr21 media are measured with ring heads to estimate the area density that can be achieved. Densities as high as 100 Mb/cm2 (1 μm2/bit) are expected when a signal-to-noise ratio sufficient for an error probability less than 10 -5 is required. As a comparison, densities estimated from data from metal-evaporated tape and CrO2 tape are given. In the frequency response of the single-layer media, an additional minimum was observed for a wavelength slightly larger than the gap length. This is probably caused by the bipolar nature of the perpendicular recording field of a ring head View full abstract»

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  • High-energy Co-Cr thin films sputtered on glass disks for perpendicular recording

    Publication Year: 1988 , Page(s): 2341 - 2343
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    The authors have developed high-energy Co-Cr thin-film perpendicular recording media for rigid disks. They obtained high perpendicular coercivity (Hc⊥) exceeding 2000 Oe with Co-Cr films sputtered on glass disks. They examined recording characteristics obtained with double-layered media and single-pole heads. Readout voltages were proportional to Hc⊥ up to 2000 Oe and not dependent on saturation magnetization. The authors explain the experimental results using the hysteresis curve of the Co-Cr film and the permeance factor determined by the magnetic reluctance of the head and medium. Using a magnetic circuit model, they clarify the effect of the difference in the operating point on the hysteresis curves of rigid- and flexible-disk systems View full abstract»

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  • Magnetic anisotropy of perpendicular media on grooved structure substrate

    Publication Year: 1988 , Page(s): 2344 - 2346
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    Magnetic anisotropies were investigated for CoCr perpendicular magnetic films on grooved structure substrates (pitch length 2.1 μm) prepared by CF4-reactive-ion etching. Perpendicular magnetic anisotropy decreases in the region where groove depth GD >650 A. The reduction is due to the inclination of the crystal growth axis on the groove surface. In-plane magnetic anisotropy, Ku||, strongly depends on GD and saturation magnetization Ms. In a region of large GD and large Ms, Ku|| is mainly due to shape anisotropy. In a region of small GD and small Ms , Ku|| is caused by perpendicular magnetic anisotropy, in addition to shape and magnetorestrictive anisotropy View full abstract»

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  • Ta additive effect on RF magnetron sputtered CoCr films

    Publication Year: 1988 , Page(s): 2347 - 2349
    Cited by:  Papers (1)
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    Magnetic properties for sputtered CoCrTa films (18 at.% Cr and 2.0-3.0 at.% Ta), which were deposited under various background pressures Pi, and argon sputtering pressures, P Ar, have been examined. The perpendicular anisotropy field Hk for CoCrTa films maintains high values of 5-6 kOe in a wide range of Pi and PAr , as compared with that for CoCr films. In order to optimize Ta composition, magnetic properties and crystalline microstructures for Ta additive content (0-4.0 at.%) have been investigated. Hk and perpendicular coercivity Hc⊥ increase with increasing Ta concentration above 2.0 at.% Ta. C-axis orientation is improved by adding Ta to CoCr films. However, above 3.0 at.% Ta, Hc⊥ steeply decreases and domain wall motion is observed, owing to the increase in crystalline grain size. The appropriate Ta composition is 2.0-3.0 at.% View full abstract»

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  • Enhanced perpendicular coercive force of CoCr film formed on a very thin initial sublayer

    Publication Year: 1988 , Page(s): 2350 - 2352
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    Perpendicular coercivity of CoCr sputtered films on Ti adhesive layers decreases drastically as RF sputtering power increases. A very thin CoCr sublayer deposited at low power enhances the coercivity of the succeeding CoCr layer. Magnetic properties and segregated microstructures show that the initial segregated microstructure is inherited by the main CoCr layer even though the RF sputtering power changes during the sputtering process. Its segregated microstructure is enhanced by the initial 100-Å segregated structure View full abstract»

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  • The effect of initial growth layer on magnetic properties of Co-Cr films

    Publication Year: 1988 , Page(s): 2353 - 2355
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    The effect of a Ti underlayer, which increases the perpendicular coercive force of Co-Cr films, was investigated. To clarify the cause of this phenomenon, the film-thickness dependence of the magnetic properties was examined. It was found that the coercive force of a Co-Cr film deposited directly on a polymide substrate decreases drastically when it becomes thinner than 50 nm, whereas in the case of Co-Cr film on a Ti underlayer, a high coercive force is maintained even when the film becomes as thin as 20 nm. The film with the underlayer has a distinct uniform columnar structure, whereas the film without it has a 50-nm-thick initial growth layer with no clear structure. Measurements of the temperature dependence of magnetic properties and observations of segregated microstructures indicate that the improvement of magnetic properties by the insertion of the Ti underlayer is mainly due to the improvement of shape anisotropy resulting from the formation of a distinctly segregated microstructure View full abstract»

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  • FeNi and Ti underlayers for vertical recording on rigid disks

    Publication Year: 1988 , Page(s): 2356 - 2358
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    FeNi and Ti underlayers on CoCr disks are studied. It is confirmed that the structure of FeNi thin films is derived from pure Ni cfc structure. Soft magnetic films can be achieved when sputtering conditions are optimized for an Fe2ONi80 target. Sputtering conditions were also studied for Ti layers. It was found that Ti thin films crystallize in the hcp structure. An (002) crystallographic preferred orientation was generally observed, but it can be improved for thinner films and when high cathode voltage is used during deposition. A (100) orientation is observed if high bias voltage is applied to the substrate during deposition. Both structures, when used as underlayers, improve the vertical anisotropy of CoCr, but (100) Ti underlayers lead to a higher vertical anisotropy View full abstract»

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  • Plasma-enhanced vacuum evaporation of perpendicular Co-Cr magnetic thin films

    Publication Year: 1988 , Page(s): 2359 - 2361
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    A novel plasma-enhanced vacuum evaporation process is described for the fabrication of perpendicular Co-Cr thin films for high-density magnetic tape recording. The plasma is excited by an RF coil placed between the source and substrate and is supported by the metal evaporant itself without the need for a carrier gas. The primary effect of the plasma is to increase the perpendicular coercivity, thus allowing a reduction in substrate temperature for better compatibility with low-temperature (and cheaper) polymer supports. It is found that Cr concentration, substrate temperature, and substrate surface preparation are critical to the development and control of perpendicular magnetic characteristics. Transmission electron microscopy (TEM) cross-section analysis reveals a slight increase in grain diameter from film bottom to top, even for films with well-oriented initial layers. A survival-of-the-tallest grain growth model in the high-mobility limit is proposed to explain some of the observed features View full abstract»

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  • Numerical micromagnetics of small particles

    Publication Year: 1988 , Page(s): 2362 - 2367
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    The results of applying the authors' micromagnetic code to a homogeneous spherical particle that is large enough to support inhomogeneous magnetization are given. For smaller particles, magnetization reversal is by coherent rotation. Larger particles initially exhibit curling as the applied magnetic field is reduced from a saturating value. Then one of two new behaviors is observed. For weak crystalline anisotropy, the axis of the curling state rotates and bends, and the magnetization reversal process is reversible, or nearly so. For strong crystalline anisotropy, a sudden discontinuous transition occurs to a vortex state with axis perpendicular to the anisotropy axis, and the vortex moves across the particle as reversal of the applied magnetic field continues. The formation and disappearance of the vortex are irreversible, but all other aspects of the process are reversible View full abstract»

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  • Discretization errors in numerical micromagnetic models

    Publication Year: 1988 , Page(s): 2368 - 2370
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    Numerical micromagnetic models attempt to determine coercive force, reversal modes, the number of stable magnetic states of particles, and the effect of particle interaction. These models can have considerable discretization error. In some cases, the calculated equilibrium states change considerably when the number of elements is increased. An analysis of three types of discretization errors suggests a measure of the accuracy of the models View full abstract»

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  • A new method for finite element calculation of micromagnetic problems

    Publication Year: 1988 , Page(s): 2371 - 2373
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    A novel method has been developed to compute static 2-D and 3-D micromagnetic structures using finite elements. The method can be applied to domain studies, i.e. bubble configuration, Bloch line memories, or magnetooptical materials. All energy terms are minimized without approximation, especially the long-range demagnetizing energy, which causes generally long running time; boundary finite elements are used in this program. The algorithm for minimizing the total energy is gradient or Newton type View full abstract»

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  • Conduction of flux at high frequencies by a charge-free magnetization distribution

    Publication Year: 1988 , Page(s): 2374 - 2376
    Cited by:  Papers (7)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    A charge-free, analytically tractable model for flux conduction by pure rotation in Permalloy strips at high frequencies is proposed. An expression for the magnetization rotation versus applied field is presented. The model is extended to give important qualitative results for shapes other than simple strips. In particular, the region where the narrow pole tip joins an abruptly widened yoke in a thin film recording head is considered. It is shown that the desired flux spreading in this region can only be achieved with accompanying wall motion View full abstract»

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  • 2-dimensional numerical analysis of laminated thin film elements

    Publication Year: 1988 , Page(s): 2377 - 2379
    Cited by:  Papers (3)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    A theoretical analysis of the laminated thin film elements is carried out by solving the micromagnetic equation. The boundary conditions of the equation are obtained by assuming that the magnetization is pinned at the edges of the elements. The dimension of the element is 2 μm×20 μm, with 150-Å-thick magnetic layers and a 50-Å-thick nonmagnetic layer. For the numerical analysis each magnetic layer is divided into 40×100 segments. The demagnetizing field is obtained by integrating the surface poles generated at the boundaries of the elements. Two different element shapes are considered: rectangular and diamond. Each shape is solved with its anisotropy constant either parallel or perpendicular to the long dimension of the element View full abstract»

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  • Domain theory model for magnetic thin films

    Publication Year: 1988 , Page(s): 2380 - 2382
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    A domain-theoretic model for external-field-driven magnetization processes in thin-film microelements is described. The film is mathematically described by a dynamic grid of quadrilateral domains whose magnetization directions and vertex locations are variables with which to minimize the total free energy. The magnetostatic interaction between uniformly (in-plane) magnetized polygonal domains is essentially treated exactly. Predicted results for reversal mechanisms and field-induced metastable remanent domain configurations in Permalloy microelements are in good qualitative agreement with Bitter pattern observations 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