The synthesis of magnetic recording trellis codes with good hamming distance properties

In this paper we present, by means of an example, a systematic procedure to synthesize combined modulation/error correcting trellis codes, suitable for Viterbi decoding. This synthesis is based on firstly selecting a suitable linear convolutional code, secondly by analysing the state system of this code to determine the important Hamming distance building properties, and finally by mapping a code with the desired restrictions on its sequences onto this state system. As an example we develop a R = 3/6 dc free (b,l,c) = (0,3,2) code withd_{min} = 4. This code improves on the best codes in [1]. Codes havingb geq 1, and which will thus be more suitable for magnetic recording, can also be synthesized following the proposed procedure.     

The influence of applied tensile stress on power loss in Co-rich amorphous Co-Fe-Si-B ribbons with induced magnetic anisotropy

The influence on power loss PTof applied tensile stress σ in amorphous (Co0.89Fe0.11)72Mo3Si15B10(lambda_{s} > 0) and Co73Mo2Si15B10(lambda_{s} < 0) ribbons with different induced magnetic anisotropy Kuis reported. The losses are measured under sinusoidal flux conditions atf = 50Hz,J_{max} = 0.57T and atf = 400Hz,J_{max} = 0.10T. Measurements are carried out on samples in a stress-relieved state and with magnetic anisotropies induced by stress or field annealing. Atf = 50Hz, a minimum m Ptversus σ is observed. The σ-value (sigma_{min}) corresponding to the minimum PTincreases with increasing |Ku|. Atf = 400Hz, a minimum in PTversus σ is observed in the samples with induced magnetic anisotropy, whereassigma_{min} = 0in the stress-relieved samiales. However, no correlation between andsigma_{min}and Kuis possible from the present data.     

Relationship of bias field setting procedure to field stability against external field perturbations for magnetic bubble memory bias field structures

In magnetic bubble memory packages having a bias field HBsupplied by a Ba-ferrite permanent magnet structure, the magnitude of HBmay be appreciably altered after setting by transient exposure to externally applied magnetic fields Hextas much as 10 times smaller than the field used in setting HB. We examine this effect for a particular magnet design having a permalloy yoke, a gap of 0.270 inches, and a saturation fieldH_{sat} simeq 240Oe. We find that the magnitude of the effect depends upon the ratioH_{B}/H_{sat}and upon the procedure used in setting HB. After setting toH_{B} = 200Oe from saturation with a demagnetizing fieldH_{ext} = -1400Oe, a remagnetizing fieldH_{ext} simeq 1800Oe is required to increase HBby 1%. On the other hand, after setting toH_{B} = 100Oe withH_{ext} = -2300Oe, a remagnetizing fieldH_{ext} simeq 400Oe is sufficient to increase HBby 1%. Setting by demagnetizing from saturation yields superior stability to setting by magnetizing from the demagnetized state, and stability of the set magnet may be further improved by demagnetizing with a ringing (alternating) field. This behavior is explained with a simple model and its importance for magnet design is discussed.     

A new magnetic alloy of high constant permeability

Several conventional alloys of constant permeability used previously were of lower values of permeability, or they would change obviously in different intensities of magnetic field and thus could not satisfy some specific requirements of electrical application. The alloys consisted of Ni 60-70 wt%, Fe 29-39wt% and Mn 0-1 wt% were investigated. The best of those alloys for certain use is 1J66 alloy in China. It is a new alloy of high constant permeability with the chemical composition as Fe 34 wt%, Ni 65 wt% and Mn 1 wt%. Its AC induction permeabilitymu_{L}= 3400G/Oe (f=60Hz). Within the range of Bm=20-6800 G, the stability of AC induction permeability (f=60Hz)alpha_{sim} = 4.3%. The α is defined asalpha = mumax-mumin/mumin,alphamaxandmuminare the maximum and the minimum of permeability respectively in the range of given magnetic field. The temperature stability αTof μLwithin the range of temperature from -60°C to +90°C is 2.9%. The saturation magnetic induction of 1J66 alloy equals 13500 G. The remanenceB_{r} < 150G. The coercive forceH_{c} = 0.05Oe. The oxygen content of 0.015- 0.04% in the alloy is considered necessary for obtaining a good stability of permeability.     

Magnetic properties of Co-Cr/mumetal double layer films

A dc magnetron sputtered multilayer (Co-Cr mumetal) film is examined for magnetic coupling of the sublayers. No evidence for physical coupling is observed. The multilayer coercivity near the perpendicular direction has a strong dependence on angle due to the planar mumetal component. The coercivity of the mumetal exhibits Kondorsky-type angular behavior. Coercivities of the Co-Cr film measured parallel and perpendicular to the field direction both decrease linearly from 100 K to 340 K, with a room temperature coefficientbeta = (1/H_{c})(DeltaH_{c}/DeltaT) = -0.2percent/K. The temperature dependence of coercivity can be modeled on a domain wall pinning theory, based on exchange fluctuations over a small domain wall area. It is shown that high Curie temperatures are needed to minimize thermal variation in recording output signal. X-ray transmission attenuation is shown to be a useful tool for determining the Co-Cr thickness in a multilayer film.     

Helical anisotropic magnetic film

The magnetic coupling between the magnetization in two nonmagnetostrictive Ni-Fe layers separated by a SiO layer has been investigated by means of a transverse susceptibility measurement. The main results are that 1) the coupling energy Ec per Unit area of the multilayered film has a form ofE_{c}= -A cos (phi_{1}-phi_{2}), wherephi_{1}-phi_{2}is the angle between the magnetization vectors in the two Ni-Fe layers, and 2) the dependence of the coupling constant on the thickness b of the intermediate SiO layer can be interpreted quantitatively by the combination of the coupling energy due to Néel's topography model and that due to the magnetostatic interaction between the magnetic free poles appearing at the edges of the two Ni-Fe layers. The former coupling energy is given byE_{c1} = -frac{p}{2sqrt{2}}omega^{2}M^{2} exp(-sqrt{2}pb) cos (phi_{1}-phi_{2})wherep=2pi/LandLandware the wavelength and the amplitude of the undulation of the interface between Ni-Fe and SiO layers, respectively. The latter is given byE_{c2} = frac{2M^{2}D^{2}}{R} ln (frac{R}{D+b}) cos (phi_{1}-phi_{2})whereDis the thickness of each Ni-Fe layer, andRis the radius of the film.     

A vector model for magnetic hysteresis based on interacting dipoles

A model for magnetic hysteresis is described in which the applied field intensity is free to rotate as well as vary in magnitude. The model is an infinite lattice of ellipsoidal Stoner-Wolfarth particles withN^{3} = 8,27,64,125,216...independent and not necessarily identical particles per unit cell. Techniques for making this simple yet very general model computationally tractable are described. The model is intended primarily for studying the magnetic recording process in particulate storage media.     

Effects of spacer layer elastic properties on metallic thin film edge-induced stress gradients in bubble memory devices

It is well-known that metallization edge-induced stresses can change the uniaxial magnetic anisotropy of a liquid phase epitaxial (LPE) garnet film near the metallization edge. We have investigated this magnetostrictive interaction of patterned metallic films with ion-implanted LPE films by using several different spacer layers such as polyimide, SiO2, Si3N4, and combinations of polyimide and SiO2beneath a Cr-Cu-Cr conductor pattern. It is concluded that the stress eliminating capability of a spacer depends on the hardness parameterK = frac{E_{s}(1-numin{f}max{2})}{E_{f}(1-numin{s}max{2})}whereE_{s} , E_{f}are Young's moduli andnu_{s}, nu_{f}are Poisson's ratios for the spacer and metallic film, respectively. The polyimide spacer withE_{s} < 10^{11}dyn/cm²and withK leq 0.1transmits an order of magnitude of smaller stress than a SiO2spacer withK geq 1with the stress being more uniformly distributed across the spacer.     

Static and anhysteretic magnetic properties of tapes

The anhysteretic remanencebar{M}_{ar}(H_{o},T)of solidified suspensions of magnetic particles with predominant shape anisotropy is calculated from first principles for small dc fields Hoand arbitrary temperatureT < T_{B}(blocking temperature), describing the particle interactions by a mean field and assuming constant decrement of the ac field,2H_{d}per cycle. ForH_{d}< 2H_{o}, the anhysteretic distribution of particle magnetizations is found to be subject to the condition that the net internal dc fieldbar{H}_{i}is a minimum, and, for small Ho, to the condition,bar{H}_{i} = 0. The theory yieldsbar{M}_{ar}(H_{o},T)as a unique function of independently measurable static magnetic material properties, i.e., it contains no adjustable parameters and is hence quantitatively related to experimental data. Further, according to theory, ifbar{M}_{ar}(H_{o},T,T_{m})denotesbar{M}_{ar}as acquired in Hoat T and measured atT_{m}, bar{M}_{ar}(H_{o},T,T_{m} = T)is independent ofTforH_{d} ll 2H_{o}, andbar{M}_{ar}(H_{o},T,T_{m} neq T) = [M_{s}(T_{m})/M_{s}(T)] cdot bar{M}_{ar}(H_{o},T,T_{m} = T). The thermoremanent magnetization acquired in Hoand measured at a temperatureT_{m} ll T_{B},bar{M}_{thr}(H_{o},T_{m}), is related tobar{M}_{ar}(H_{o},T = T_{m}, T_{m})bybar{M}_{thr}(H_{o},T_{m}) = [M_{s}(T_{m})/M_{s}(T_{B})]bar{M}_{ar}(H_{o},T=T_{m},T_{m}), where TBis the blocking temperature below whichbar{M}_{thr}becomes thermally stable. Up to a constant factor of about 2, the theoretical results agree quantitatively with the experimental data on all materials that correspond to the premises of the theory, i.e., solidified suspensions, tapes in particular, of particles having predominant shape anisotropy.     

Exchange-Coupled IrMn/CoFe Mulitlayers for RF-Integrated Inductors

The high-frequency characteristics of the RF integrated inductors with antiferromagnetic/ferromagnetic (AF/F) multilayers (MLs) are studied. Each AF layer is 8-nm IrMn and F is Co₅₀Fe₅₀ with a 200-nm splitting into N = 1 to 5 repeats of MLs. This exchange coupled {IrMn/CoFe(d nm)}_N MLs are deposited on top of the two-port inductors with five-turn square spiral coils, a dimension of 100 mum times 100 mum and line/space of 5 mum/2 mum. The inductor surface and magnetic layer is separated by 1-mum-thick SiO₂. The enhancement of inductance (DeltaL) is 20% compared to an air-core of the same coil size. The resonance peak gradually shifted to a higher frequency with increasing N, and reached at a maximum of 4.3 GHz when N = 5. This is in good agreement with our magnetic data which revealed that the anisotropy field (H_k) and ferromagnetic resonance frequency (f_FMR) of {IrMn/CoFe(d nm)}_N MLs are increased with increasing N. The quality factor, Q is improved by 6.8% at 1.5 GHz for the {IrMn/CoFe(40 nm)}_N=5 integrated inductors compared to air-core inductors.     

The vibrating head magnetometer--Instrument for the measurement of magnetic transitions in high coercive force films

The magnetization pattern recorded in high coercive force media, such as magnetic tapes or discs, is measured with the vibrating head magnetometer (VHM) by vibrating a recording head parallel to the surface of the medium and along the track length. The VHM can be used with small, irregular-shaped samples. It can be used to measure precisely the shape of recorded magnetic transitions. Application of the VHM to the precise location of dropouts on prerecorded samples and to the alignment of a recording head with respect to a prerecorded track is described. Measurements have been made with the VHM of the half peak width and relative peak signal of isolated transitions in Co alloy films. The half peak width was found to be proportional to(t/H_{c})^{0.5}.     

Representation of the magnetization characteristic by a sum of exponentials

It is possible to set up equations of the formB(H) = a_{0} + a_{1} e^{-alpha_{1}H} + a_{2} e^{-alpha_{2}H} + a_{3} e^{-alpha_{3}H} + a_{4} e^{-alpha_{4}H}on an analog computer to fit accurately aB-Hcurve of any magnetic material over the whole range from zero to the knee of the curve to the saturation part of the curve.     

Side fringing fields and write and read crosstalk of narrow magnetic recording heads

In magnetic recording systems the side fringing fields of magnetic recording heads are responsible for crosstalk from adjacent tracks and eventually for partial erasure of adjacent tracks, thereby limiting the attainable track density. In this paper we derive analytical expressions for the magnetic field near the side of a recording head and calculate the cosine transform of the longitudinal field component, with the head side angle and gap length as parameters. The field of a head of zero width is also considered. Due to the side fringing field the written track is somewhat wider than the geometrical head width; the increase in width being approximately proportional to the maximum field strength in the recording medium and the head-to-medium distance. The amplitudeuof the read crosstalk signal from an adjacent, infinitesimally narrow track is calculated and it appears that it can be approximated byu/u_{0} = 0.5 exp (-2pi x/lambda), where u0is the on-track signal (with zero head-to-medium spacing),xis the distance between track and head side, and λ is the wavelength. Maximum track densities are calculated for a specified crosstalk-to-signal ratio and a given head width and wavelength. For a wavelength of 10 μm, a head width of 5 μm, and a crosstalk of -20 dB, the track density is limited to about 130 tracks/mm, assuming a track width equal to the head width. When the track is taken to be 5 μm wider than the head to account for the effects of the write process, no guardband at all is needed for -20 dB crosstalk and the limit to the track density is 100 tracks/mn.     

The development of <100> texture in Fe-Cr-Co-Mo permanentmagnet alloys

The cold-rolled and recrystallization textures of Fe-Cr-Co-Mo permanent magnet alloys are described. The studied composition is Fe-30%Cr-15%Co-3%Mo (in wt.%). The cold-rolled texture can be considered to be {111}<110>, {111}<112>, {100}<110>, and {211}<110>, while the recrystallization texture can be considered to be {111}<100>, {110}<112>, {211}<110>, and {110}<110>. The secondary recrystallization is caused by heat-treating the alloys in the sequence of α, α+γ, α+γ+σ, α phase region. This results in a favorable texture of {110}<110> and <100> direction, aligning along the transverse direction (TD) of the strips. The best magnetic properties obtained in this study were 1.2 T (12.0 kG), iH _c=82.0 kAm^-1 (1025 Oe), and (BH)max= 60.8 kJm^-3 (7.6 MGOe) with TD alloys     

Self-consistently computed magnetization patterns in thin magnetic recording media

A model involving head motion is given for self-consistently computing magnetic recording medium magnetization patterns. The reduction in demagnetizing field due to the presence of the high-permeability head structure is included, as is record head removal, read head replacement, and computation of the readback voltage. The model is capable of handling an arbitrary record current waveform. Optimum record-current amplitude for nonreturn to zero (NRZ) digital recording is first determined, and then single-, double-, and quadruple-transition computations are performed using two different values of hysteresis loop squarenessM_{r}/M_{s}and both linear and exponential current reversals. Results are primarily for the Karlquist fringe field, but the recording properties of a head exhibiting regions in which the fringe field reverses sign are also briefly investigated.     

Models of elastic and inelastic flux switching

The totaldot{phi}(t)waveform of a square-loop magnetic core switched by MMFF(t)from negative remanencephi = -phi_{r}is composed of elasticdot{phi}_{epsilon}(t), decaying inelasticdot{phi}_{i}(t), and bell-shaped main inelasticdot{phi}_{ma}(t). The worst delta noise in a coincident-current memory core pair is essentiallydot{phi}_{i}(t). The sources of these components and the staticphi(F)curve are explained qualitatively by means of the random variations of the energy gradient vs. domain-wall position: elastic wall displacements and elastic rotation of magnetization inducedot{phi}_{epsilon}(t); minor inelastic wall displacements of essentially constant wall areas inducedot{phi}_{i}(t); and major inelastic wall displacements (involving domain collisions) of varying wall areas inducedot{phi}_{ma}(t). Semiempirical models for thedot{phi}components are based on the characteristics of these displacements. A satisfactory agreement is obtained between these models anddot{phi}(t)oscillograms of a thin ferrite core.     

Preparation of thin films in the system γFe2O3- Fe3O4for recording media by spray pyrolysis of organometallic solutions using an ultrasonic pump

Thin films of magnetic spinel iron oxides were prepared by pyrolysis of an ultrasonically generated aerosol of organometallic compounds. The bases of the method and experimental procedure are described. Polycrystalline films of good adherence and homogeneity were obtained. Lattice parameters were observed to be modified by film substrate strain interaction and to depend strongly on the hydrogen content. The oxidation state of iron was discussed in regard to the experimental growing conditions. Corresponding magnetic properties were investigated. Pure magnetite Fe3O4films withH_{c} = 400Oe andM_{s} = 400EMU/cm³and gamma ferric oxides films withH_{c} = 400Oe andM_{s} = 250EMU/cm³have been obtained without post deposition heat treatment. Annealing magnetite films in air resulted in a considerable increase of their coercivity (up to 800 Oe).     

Measurements on permanent magnets made from misch metal-cobalt alloy powders

Powders of a misch metal-cobalt alloy of type (MM)Co5were prepared and consolidated in various ways to study the effects of particle size, plastic deformation during milling, and pressure applied during compacting on the permanent magnet properties. Vibration grinding yields particles with high coercive force (MH_{c} = 4180Oe) but which align very poorly in a field. Mortar-ground powders have high magnetic anisotropy combined with much lower, but strongly particle-size dependent Hc. Ballmilling, a method suitable for production in quantity, constitutes a satisfactory compromise. Pressing ballmilled powder in a field with 3400 kg/cm²pressure and no binder gave optimum results. A magnet havingMH_{c} = 2010Oe,BH_{c} = 1620Oe,B_{r} = 4060G, and(BH)_{max} = 2.34MG.Oe was obtained. Details of the static and recoil behavior for this magnet are reported.     

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

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 atsim100degC 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 of1.1 times 10^{17}2-MeV e/cm², the relative change in remanence (DeltaB_{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 (DeltaH_{c}/H_{c}) also depends upon the preirradiation value of remanence, but in a different way. ForB_{r} < 5000G,DeltaH_{c}/H_{c}is either negative or zero. ForB_{r} > 5000G,DeltaH_{c}/H_{c}is positive, ranging from 20 to 150 percent, and increases linearly withB_{r}; 3) if the dose is reduced tosim0.8 times 10^{17}e/cm², thenDeltaH_{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.     

Recording characteristics of electroless-plated perpendicular media for flexible disks

The read/write characteristics of electroless-plated perpendicular magnetic recording media for flexible disks were studied using commercial VHS and 8-mm VTR ring heads. Excellent results were shown for a medium composed of Co-Ni-Re-P plated on a non-magnetic electroless-plated Ni-P layer. A Ni-P underlayer of only 500 Å greatly improved the read/write characteristics of the disk. Reproduced signals over 300 kFRPI were observed for a system using a VHS head, andD_{50} = 134kFRPI was obtained using an 8-mm head.