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Magnetics, IEEE Transactions on

Issue 4 • Date December 1965

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Displaying Results 1 - 25 of 41
  • [Front cover and table of contents]

    Publication Year: 1965 , Page(s): 0
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    Freely Available from IEEE
  • Administrative committee members

    Publication Year: 1965 , Page(s): 245
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  • An electroplated 84Fe-5Ni-11Cu isotropic thin film for the cubic waffle-iron

    Publication Year: 1965 , Page(s): 246 - 250
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    The information storage media in the cubic waffle-iron memory is a square loop, isotropic, medium coercive force planar film called the overlay, which is placed in contact with ferrite posts. An 84Fe-5Ni-11Cu alloy has been developed to meet the requirements of the waffle-iron overlay. The film is electrodeposited on a specially prepared 2 frac{1}/{2} by 1 frac{1}/{4} by 0.040 inch copper substrate. The basic waffle-iron cell has an area of 30 mils by 30 mils, yielding a storage density in the film of 1100 b/in2. The film has a coercive force of 10 Oe, 0.9 squareness ratio, 7000-Å thickness, and 0.52 Oe-μs switching coefficient. The preparation technique of the substrate has resulted in a 75-percent yield of films in which every bit output exceeds a level of 5 mV. Operational data has shown output uniformity to be maintained within ±10 percent. A corrosion study at 95°F and 90-percent humidity of eight protective coatings has resulted in the choice of Acryloid lacquer as the protective coating for the iron-rich alloy. This coating, which is applied evenly by a controlled dipping process, also provides electrical insulation between the film and the drive windings. Preliminary results of a six-month aging study at 60°C show no significant change in the hysteresis loop of the films. View full abstract»

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  • Magnetostatic wall interaction effects in multilayer films

    Publication Year: 1965 , Page(s): 251 - 253
    Cited by:  Papers (4)
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    The critical film thickness for Bloch-Néel (B-N) wall-type transition has previously been determined experimentally for the configuration of two parallel and equally thick 81 percent Ni-19 percent Fe films separated by a nonferromagnetic layer of SiO as a function of the thickness of the separating layer. The experimental results are interpreted assuming a simple coupled-wall model and using the Néel approximation for wall width and wall energy calculations. View full abstract»

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  • Dependence of coercivity on driving field in multilayer films of nickel

    Publication Year: 1965 , Page(s): 254 - 257
    Cited by:  Papers (3)
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    The variation in the coercivity of magnetization loops of multilayer films of nickel was investigated as function of the rate of rise r in the applied magnetic field. The films were prepared by deposition of nickel and copper alternately in a vacuum of 2 \times 10^{-6} mm of Hg on to substrates made of thin aluminium foils. The thickness of the nickel layers L varied in the different films from 8 to 1000 angstroms. The loops were cycled with sinusoidal or triangular waveform driving fields, with a variety of amplitudes from 1 kOe to 4 kOe, with frequencies from 0.01 to 2 c/s. The measurements were performed from room down to liquid hydrogen temperatures. It was found that the coercive force could be expressed by H_{c} = H_{o} + Q(\ln r - \ln r_{o})/T^{1/2} for values of r changing from 1 to 5 Oe/ms, where H_{o}, A and rovaried slightly with temperature T . The coercive force was a very sensitive function of L and of the thickness δ of the copper layers, having the form H_{c} = A(L + \delta ) \exp - BL with B nearly constant in films deposited on a substrate at room temperature. The dependence of the coercivity on L was displayed by a nonmonotonical function showing two peaks in Hccorresponding to values of L of about 35 and 400 angstroms. The observed dependence of Hcon the rate of rise in the applied field, as well as on the thicknesses of the layers, can be discussed on the assumption of nonuniform magnetization within the thin layers as a result of their superparamagnetic properties and of the magneto-statical coupling between neighboring layers. View full abstract»

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  • Switching processes in thin ferromagnetic film memory elements

    Publication Year: 1965 , Page(s): 258 - 262
    Cited by:  Papers (3)
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    The switching properties of small, rectangular areas of thin ferromagnetic films, relevant to their utilization as memory elements in digital computers, are discussed. An attempt is made to derive the switching properties theoretically by superposition of the calculated demagnetizing field effects upon the known intrinsic film properties. Experiments performed using homogeneous quasi-static applied fields show good agreement with the theory. In the case of high easy direction applied fields the complexity of the magnetization distributions necessitates a number of simplifying assumptions in the theoretical treatment, and here the agreement is poorer. The treatment is sufficiently accurate to yield relationships between the intrinsic film properties, the dimension of the element, and the available output flux. In practical configurations the element is switched by inhomogeneous fields produced by fast current pulses in strip lines, and its state is ascertained by the observation of an EMF induced by the rotating magnetization. The differences between the configuration observed here and the practical one are discussed. View full abstract»

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  • Temperature effects on film memory drive current margins

    Publication Year: 1965 , Page(s): 263 - 266
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    Negligible reversible changes in magnetic properties of thin metallic films exhibiting high Curie temperatures are expected over normally encountered temperature ranges. However, irreversible changes of the magnetic properties of vacuum-deposited films have been observed when they are subjected to high magnetic fields at temperatures in the order of 100°C. A similar effect is also observed in some electroplated films at lower temperatures. This investigation attempts to determine the significance of these effects in vacuum-deposited planar films when operated in a practical memory. Reversible and irreversible temperature-induced changes of restore digit current and disturb digit current thresholds, IdRand IdD, respectively, due to pulsed word and digit fields, were measured experimentally for temperatures between 20°C and 135°C. The pulsed fields simulated typical operational word and digit fields. Average threshold variations are given and discussed. Data on average film output variations is also presented. View full abstract»

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  • Permalloy film NDRO memory

    Publication Year: 1965 , Page(s): 266 - 271
    Cited by:  Papers (1)
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    A thin magnetic film NDRO storage cell has been developed for very high-speed word-organized memories. The storage cell contains two 500-Å, 15-mil-square Permalloy film elements with a read and sense line between them. One film element is deposited on a metallic ground plane, so that the read line and its image in the ground plane are coupled to the readout film and decoupled from the storage film. A 3-ns-wide 300-mA read pulse with a 1-ns rise time yields a 4- to 6-mV output signal. Two methods of coincident current writing were investigated. One with the word and digit lines outside the storage cell required 500-mA word current, 80-mA digit current, and a read after write pulse. Writing takes 50 ns and the storage cell will tolerate coincident word and digit disturb currents of 50 and 100 mA, respectively. The other method uses the read and sense lines between the films as word and digit lines. Word currents of 300 mA and digit currents of 50 mA are required to write. The disturb margins are greater, and read after write pulse is not required. Because the eddy currents in the ground plane must decay, writing takes 3 μs. A 512-word, 40-digit test plane has been built and partially populated to determine problems in building a large array. The characteristic impedances and effects of attenuation and delay have been observed. In particular, the output signals are reduced one half because of attenuation and the difference in signal propagation time in the two directions on the sense line. View full abstract»

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  • Integrated transmission lines for magnetic thin film memories

    Publication Year: 1965 , Page(s): 272 - 276
    Cited by:  Papers (4)
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    The pulse transmission properties of integrated strip lines are examined for a structure that has been proposed for application in a large capacity, high-speed magnetic film memory. The lines are vacuum-deposited onto an insulated ground plane and are characterized by low impedances. Previous analyses, such as those given by Eastman and Chang, McQuillan, and Harloff, examine the effects of skin-depth losses in lines which are assumed to be perfectly terminated. In general, this type of analysis is insufficient for lines which are lossy and which have resistive terminations. The present analysis considers skin-effect losses in the ground plane and in the strip conductors separately and also includes the effect of reflections from resistive terminations. The influence of heavy magnetic loading of the transmission line due to the presence of magnetic film devices is examined in detail. A computer program, similar to the one described by Bertin, has been used to obtain numerical results for the pulse response of the transmission lines. Data are presented which demonstrate the influence of line geometry and material properties. View full abstract»

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  • Uniaxial anisotropy by "radiomagnetic" treatment; controlling factors in a new process

    Publication Year: 1965 , Page(s): 277 - 280
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    A new process-an electron-"radiomagnetic" treatment-for obtaining high-remanence, low-coercive-force loops in magnetic alloys was recently announced. As an example, 2-MeV electron irradiation of 6-mil-thick ring laminations of polycrystalline 5-80 Mo Permalloy with 1017e/cm2in an applied circumferential magnetic field of 0.2 Oe at \sim100\deg C produced record highs in remanence (∼6700 G) for this material. Additional studies of this process have been made to determine some of the controlling factors and the range of application. In particular, the effects of the dose (number of e/cm2) and of the preirradiation magnetic properties were examined. The results show that: 1) for a given dose of 1.1 \times 10^{17} 2-MeV e/cm2, the relative change in remanence ( \Delta B_{r}/B_{r} ) is always positive, ranging from 10 to 50 percent, but varies inversely with the preirradiation value of remanence (Br); 2) for the same dose, the relative change in coercive force ( \Delta H_{c}/H_{c} ) also depends upon the preirradiation value of remanence, but in a different way. For B_{r} < 5000 G, \Delta H_{c}/H_{c} is either negative or zero. For B_{r} > 5000 G, \Delta H_{c}/H_{c} is positive, ranging from 20 to 150 percent, and increases linearly with B_{r}; 3 ) if the dose is reduced to \sim0.8 \times 10^{17} e/cm2, then \Delta H_{c}/H_{c} is reduced to a tolerable level (∼10 percent) with no significant sacrifice in the positive gain in remanence and rectangularity. Hence, there are optimum dose ranges in the "radio-magnetic" treatments of alloys, where significant gains in remanence may be obtained without appreciable increases in coercive force. View full abstract»

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  • A magnetic shift register employing controlled domain wall motion

    Publication Year: 1965 , Page(s): 281 - 284
    Cited by:  Papers (6)  |  Patents (13)
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    A shift register based on controlled domain wall propagation in a magnetic wire with an axial easy direction has been developed. The operational characteristics of an experimental model are discussed. Some hard drawn magnetic materials have been shown to have at least a 3-to-1 nucleation-to-propagation threshold field window over several hundred foot lengths of wire which guarantees operation, This is accomplished without putting the wire under tension. One such promising material is a modified 79-percent Ni, 17- percent Fe, 3-percent Nb, 1-percent Ag, permalloy. An experimental 5 \times 10^{3} -bit shift register has been constructed with 0.8-mil hard drawn Nb, Ag permalloy and operated at speeds of 5 \times 10^{3} bps with 12-percent drive current margins. The input power at this rate is approximately 1 mW/bit. View full abstract»

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  • Wide PRIME-current range for all-magnetic shift registers

    Publication Year: 1965 , Page(s): 285 - 292
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    In an all-magnetic resistance-type shift register, a PRIME current pulse i_{p}(t) , of amplitude Ip, is applied to Npand Nbturns through the minor and major apertures, respectively. For given operation frequency f , the ratio R = I_{p}^{\max }/I_{p}^{\min} , where I_{p}^{\min} < I_{p} < I_{p}^{\max } is the PRIME range of bistable operation, is maximized by matching N_{p}/N_{b} so that I_{p}^{\max } values determined by spurious ZERO buildup and ONE dropout are the same. For a rectangular (or dc) i_{p}(t) , the matched N_{p}/N_{b} is fixed by the core properties, and Rmaxis limited (e.g., <7). However, if i_{p}(t) rises gradually, the matched N_{p}/N_{b} depends also on the rise time Trof i_{p}(t) . The lower f is, with corresponding larger Tr, the smaller is the matched N_{p}/N_{b} , and the larger is Rmax. Calculation of R is carried for ramp and half-sinusoidal i_{p}(t) waveforms. The latter, for instance, at T = 25\deg C yields Rmaxvalues of 14.0 and 22.0 for f of 1.0 and 0.5 kc/s respectively. Such wide PRIME ranges permit reliable register operation in a wide temperature range without resorting to temperature compensation of Ip. Experimental results are in agreement with the calculation. View full abstract»

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  • Phenomenological model for the BIAX

    Publication Year: 1965 , Page(s): 292 - 295
    Cited by:  Papers (1)
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    This paper describes a model developed for the operation of the BIAX as applicable to an NDRO memory system. The role of a field transverse to the storage direction during writing is described. Factors contributing to the output and to the back voltage are pointed out to explain the ratio observed between these two. These individual contributions arise from rotation of the magnetization vector and changes in the dispersion angle during interrogation. A mechanical analogy is presented for the asymmetry of the NDRO observed under high-speed operation. View full abstract»

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  • Sampling and analog recording with square-loop magnetic devices

    Publication Year: 1965 , Page(s): 296 - 299
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    Square-loop magnetic devices have been used traditionally in digital circuitry. Methods by which a combination of the square-loop and time-limited switching properties of magnetic devices can be used to sample and record a transient signal are described. These circuit functions have been previously performed by rather complicated electronic means. Magnetic sampling and recording has several advantages over previously used methods: 1) circuitry is simple; 2) magnetic elements are less sensitive to some types of environmental conditions; 3) the recording and sampling is performed in a single device; 4) sampling duration can be made short enough to obtain high-frequency response; and 5) an extremely wide variety of recording problems can be solved with these devices. View full abstract»

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  • The theory of ratchet writing in multipath magnetic cores

    Publication Year: 1965 , Page(s): 299 - 308
    Cited by:  Papers (2)
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    Ratchet writing is a method of writing information into certain nondestructive-readout (NDRO) magnetic memory elements. Writing is accomplished by reversing (or "ratcheting") the flux about one hole of the element with a word-oriented wire while simultaneously applying information-determined bit current to another hole called the storage hole. The effect of ratcheting is a threshold reduction for switching about the storage hole. It is established that ratchet writing is possible because some of the flux switched by the ratchet current closes by returning around the storage hole rather than through the "common volume" between the two holes. The detailed switching properties of a simple thin-wall core are computed and compared with experiment. The results are in excellent agreement within the limitations of the approximations made. It is found that there is a region where the bit-current threshold declines linearly with unit slope as ratchet current is increased. In this region there is a direct transfer of flux from the ratcheted hole to the storage hole, the common volume remaining an open circuit. View full abstract»

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  • Switching properties of a partially set square-loop ferrite core

    Publication Year: 1965 , Page(s): 309 - 314
    Cited by:  Papers (7)
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    The switching properties of a partially set square-loop ferrite core depend not only upon the initial flux level, but also upon how that flux level was attained, and are therefore complex. Experimental results that describe some of this history dependence are presented. A thin-ring core ( OD/ID = 1.10 ) was partially set by switching it from negative remanence ( -\phi_{r} ) to some flux level (φps) using a rectangular PARTIAL SET pulse of duration Tps. This pulse was followed by a rectangular TEST pulse having a variable amplitude F to determine the properties of switching from each partially set state. Three types of data were taken during the TEST pulse: 1) switching voltage waveforms [i.e., \phi(t) ] for a given φpsand F , with Tpsas a parameter, 2) peak switching voltage vs. F [i.e., \phi_{p}(F) ] curves for a given φps, with Tps, as a parameter, and 3) \dot{\phi}_{p}(F) curves for a given Tps, with φpsas a parameter. The \dot{\phi}(t) waveforms changed considerably as Tpswas varied, even though F and φpswere constant (e.g., peaking time was reduced from 0.5 μs to less than 0.1 μs as Tpswas reduced from 100 μs to 5 ns). The slope and threshold of the \dot{\phi}_{p}(F) curves were lowered considerably as φpswas increased from -\phi_{r} to -0.36\phi_{r} (e.g., the slope was reduced by 40 percent and the threshold was reduced by 14 percent for T_{ps} = 0.9 \mu s). Presently used switching models are not able to account for these effects. Related phenomena also occur when the core is switched from -\phi_{r} with an MMF which is not constant throughout the entire switching process. The experimental results are discussed relative to the future development of an appropriate switching model. View full abstract»

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  • Technique for determining the speed capabilities of 2D ferrite core memories

    Publication Year: 1965 , Page(s): 315 - 320
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    A new and powerful method has been developed which makes possible an analytical study of the sensitivity of 2D memory cycle times to most of the pertinent memory variables. Worst-case conditions in a 2D ferrite core memory have been considered. The analysis allows independent variations (from nominal) of all drive pulse amplitudes and widths, plus variations in the thresholds of the cores caused by manufacturing. Also included are the efficiency of the thermal packaging and the effects of partial switching. In the analysis, the nonmagnetic times (time for regeneration, array delays, etc.) are lumped into a single non-magnetic delay time. The analysis results in a set of simultaneous equations interrelating all the pertinent memory variables. A set of characteristic curves is determined experimentally for the particular core type being evaluated. From these curves, 18 constants, which allow the various core properties to be analytically described, are extracted. The simultaneous equations were programmed for machine solution so that, upon the injection of 18 core constants, the speed capabilities of that particular core type could be fully evaluated in about one minute. This technique allows the core to pick its own nominal operating current amplitudes and durations. This is important since, otherwise, there is no way of being sure that the pulses picked for a core at ambient temperature will be satisfactory when the core runs hot in a worst-case cycle. The results found when applying this new method to high-speed 2D ferrite memory cores are included. View full abstract»

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  • Measurement of useful properties of memory devices

    Publication Year: 1965 , Page(s): 320 - 323
    Cited by:  Papers (1)
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    It is customary to measure properties of a memory device in terms of a specific mode of memory operation. Estimating device properties relevant to a different operating mode is usually difficult, if not impossible. At the present time, memory configurations are growing in number and in basic function, ranging widely in size, speed, power, and read/write patterns. It is often necessary to select an available device for a new memory scheme. It is occasionally of interest to select a memory scheme to make best use of a device. A set of simply measured characteristic curves is proposed, which would make it possible to evaluate a given memory device in a large number of operating modes. The quantities involved are the flux, switched by pulses limited in time, amplitude, and number; reversible and irreversible flux switching; and dc properties. Examples of the use of the curves are given. View full abstract»

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  • Continuous sheet sensing for random access memories

    Publication Year: 1965 , Page(s): 324 - 329
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    Magnetic and superconductive random access memories contain arrays of flux storage elements or sites, each of which is intersected by two selection lines used to switch flux, and one sense line used to detect flux changes. The need to have three lines intersect at many storage locations produces severe alignment problems in the fabrication of high-density deposited film memories. This paper explains and analyzes a recently announced sensing technique that operates by detecting the voltage drop caused by eddy currents induced in a normal continuous metal sheet whenever the flux linking it changes. The method is found to operate at room and cryogenic temperatures, and overcomes the alignment difficulties of the sense line technique. View full abstract»

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  • Factors affecting the sensitivity of gamma-level ring-core magnetometers

    Publication Year: 1965 , Page(s): 330 - 337
    Cited by:  Papers (17)  |  Patents (2)
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    A theoretical and experimental analysis has been made of the geometrical and magnetic factors affecting the sensitivity of the ring-core magnetometer first introduced by Geyger in 1961. Using a drive-to-pickup transfer function derived from an assumed dynamic hysteresis loop and a given dc input signal, the second-harmonic output voltage was derived for both current-source and voltage-source driving conditions. Results of the analysis, which were confirmed by experiment, show the following. 1) When a single, diametrically wound (solenoid-type) pickup winding is used with a ring-core sensor, simultaneous minimization of both fundamental and second-harmonic feedthrough can be achieved by a simple rotational adjustment. This optimization is possible only with a circular core. 2) Sensitivity can be increased by increasing frequency, number of pickup turns, dynamic differential permeability, cross-sectional area, and effective sensor length, and by decreasing the dc initial permeability (μ0). 3) The dominant factor affecting the sensitivity is the demagnetizing term \mu_{0}K = \mu_{0}l^{-1.72} (4A/\pi)^{0.86} , which determines the entrance attenuation of the dc signal to be measured. Highest sensitivity is obtained when \mu_{0}K is small, which requires a low initial permeability, since a large dimensional ratio l/A^{1/2} is usually not attainable. When the demagnetizing term is not small, the sensitivity advantages of the other factors are negated by the input signal attenuation. Power considerations show that increasing sensitivity by raising area, length, or frequency results in increased power consumption. However, increasing sensitivity by using a pickup coil with a larger number of turns or by a sensor core with lower initial permeability can be achieved without additional power. View full abstract»

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  • On the analysis of second-harmonic modulators

    Publication Year: 1965 , Page(s): 337 - 341
    Cited by:  Papers (2)  |  Patents (1)
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    Analysis of magnetic modulators, which includes low-level transducer amplifiers and magnetometers, usually is based on control-signal displacement of fixed hysteresis loops of some particular shape. Experience shows, however, that many qualitative aspects of the device operation do not agree with the analysis. In this paper, an analysis is based on the d\phi/dt widening of the hysteresis loop, which is applicable to metal alloy tape cores. The analysis makes possible the comparison of amplifiers using different magnetic materials by relating small-signal gain and output waveform to measurable properties of the material. View full abstract»

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  • A magnetic time division multiplexer for use in control circuits

    Publication Year: 1965 , Page(s): 341 - 343
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    The essentially magnetic multiplexing system described uses saturable inductors and diodes interconnected so that sending and receiving ends of the information link operate as synchronous switches slaved to the ac line. The switching rate is proportional to the number of channels desired. The information may be encoded singly, simultaneously or serially; or in combination, simultaneously or serially; provided the pilot devices remain energized for at least one cycle of the ac supply voltage. View full abstract»

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  • Digital recording properties of evaporated cobalt films

    Publication Year: 1965 , Page(s): 344 - 348
    Cited by:  Papers (22)
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    Thin coatings of cobalt, cobalt-nickel, and cobalt-phosphorous have been in use for some years as a medium in recording drums. Recent papers [1]-[3] have described the recording properties of chemical- and electro-deposits on flexible plastic bases for in-contact digital tape recording. The BH loop squareness and high coercivities achievable in films of a few microinches thickness makes them particularly suitable for high packing density storage. This paper describes the preparation and recording properties of vacuum-deposited cobalt films of varying thickness and coercivity. Comparisons made with oxide tapes show that a marked improvement in packing density is achievable. Correlations between pulse width and amplitude with thickness and magnetic properties throw some light on the mechanism of pulse recording. View full abstract»

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  • A correlation between magnetic properties and recording behavior in metallic chemically deposited surfaces

    Publication Year: 1965 , Page(s): 348 - 352
    Cited by:  Papers (18)
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    One of the most intriguing problems in understanding the recording behavior of thin metallic surfaces is to determine the extent to which this behavior depends on and correlates with the magnetic properties of the surface. From the point of view of demagnetization it is obvious that the recording surface with the best high density resolution is one that has zero moment; unfortunately, this surface also has zero signal. It is apparent from this limiting case that there exists at any given composition-subject to a minimum acceptable signal-to-noise ratio-an optimum moment for any particular recording density. Furthermore, the coercivity and the steepness of the sides of the hysteresis loop are also implicated in determining the ability of the surface to resist demagnetization and to match the writing transducer field gradient. View full abstract»

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  • A computer simulation of the magnetic recording process

    Publication Year: 1965 , Page(s): 352 - 357
    Cited by:  Papers (13)
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    This paper describes a new method of analyzing the saturation magnetic recording process using digital computer simulation techniques. This model closely simulates the physical system and avoids the usual mathematical approximating expressions for the various recording functions. In addition, automatic consideration of nonlinear effects such as recording demagnetization and finite recording current rise time are included. The real power of such a model lies in its high computational speed such that accurate results can be obtained quickly and economically for numerous sets of operating conditions. With the use of an output plotter, the results are obtained in a visual form which is particularly easy to analyze. Of fundamental importance in simulating the system is the point or particle concept utilized by this model. The recording medium is divided longitudinally into sections and all system functions are quantized at these intervals. Writing is simulated by stepping the medium particles across the head field to obtain each particle's field history, and hence, magnetization. The convolution integral describing the readback process is then readily carried out using point by point multiplication and summation of this magnetization and the head field function. The case of an infinitely thin laminar medium is used as a basis and the results are shown to correspond to previously published work. Analysis of finitely thick media then leads to a number of significant results which include the optimization of the system parameters, detailed effects of thickness (including the infinitely thick case) and the influence of recording demagnetization with various bit patterns. Experimental results are given which show good agreement with the computed predictions. It is concluded that this new method is an extremely valuable tool for the analysis and design of a magnetic recordings system, and some extensions of the method are outlined. View full abstract»

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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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Pavel Kabos
National Institute of Standards and Technology