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Magnetics, IEEE Transactions on

Issue 3 • Date May 2001

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  • IEEE Transactions on Magnetics 2001 subject categories

    Publication Year: 2001 , Page(s): 1187 - 1188
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  • Concise, efficient three-dimensional fast multipole method for micromagnetics

    Publication Year: 2001 , Page(s): 1078 - 1086
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    This paper presents derivation of the three-dimensional (3-D) fast multipole method for use in calculating magnetostatic fields. Many other derivations use complex, inefficient, and awkward function normalizations. In this derivation, tensor functions and an operator are defined that greatly simplify the theory and implementation of the algorithm. This paper provides proof of O(N) scaling, implementation, and parallelization tips, performance results, and an error analysis View full abstract»

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  • Application of a homogeneous Dirichlet boundary condition in the finite element analysis of power cables

    Publication Year: 2001 , Page(s): 1087 - 1090
    Cited by:  Papers (2)
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    We discuss the application of a homogeneous Dirichlet boundary condition in the finite element analysis of power cables. In particular, after theoretical derivation and numerical tests, we apply the boundary condition in the analysis of underground pipe-type cables. We compare the numerical results with measurement data for validation View full abstract»

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  • Effect of throat height reduction in gapped heads

    Publication Year: 2001 , Page(s): 1141 - 1145
    Cited by:  Papers (1)
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    This paper describes an investigation, based on finite-element models, of the effect of throat height reduction in gapped heads constructed from realistic, saturable materials. It considers materials and two gap region geometries. It shows that throat height reduction in a gapped head improves both the maximum horizontal field and the maximum horizontal field gradient provided that saturation does not partially block the flux path toward the gap. Saturation of planar heads limits both the maximum horizontal field and the maximum horizontal field gradient at higher throat heights than it does in conventional gapped heads. The paper shows that the optimum write field of a conventional gapped head is both stronger and sharper than that of a planar one View full abstract»

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  • Novel method for minimizing track seeking residual vibrations of hard disk drives

    Publication Year: 2001 , Page(s): 1146 - 1156
    Cited by:  Papers (1)
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    Track access time is an important parameter for high-performance hard disk drives (HDDs). Presently, the resonances of the head actuator caused by the pivot-bearing stiffness are an even more urgent problem, since these resonances have become the main design factor that limits further reduction of track access time and improvement of the servo control bandwidth in HDDs. Our objective in this paper is to investigate, from a mechanics and dynamics viewpoint, the influence of the driving force waveforms on residual vibrations and to identify the characteristics of the waveform, which will lead to zero or very low residual vibrations. Using a simplified model of a head actuator assembly and finite-element simulation, we show that the residual vibration of the head actuator assembly depends strongly on the waveform and the time duration of the driving impulse force. If suitable waveform and time duration of the seeking impulse force are appropriately chosen, very low track seeking residual vibrations and quick track access can be achieved View full abstract»

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  • Mechanical behavior of axially magnetized permanent-magnet gears

    Publication Year: 2001 , Page(s): 1110 - 1117
    Cited by:  Papers (3)  |  Patents (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    We studied permanent-magnet (PM) gears with axially magnetized permanent magnets and a plane air gap in terms of mechanical behavior. We determined the torque and forces exerted between the two rotors of these devices, using a seminumerical method based on the calculation of the forces between the magnets of the rotors. The study deals with the general behavior of such devices and presents some very interesting configurations for their mechanical stability View full abstract»

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  • Integral solution of nonlinear magnetostatic field problems

    Publication Year: 2001 , Page(s): 1070 - 1077
    Cited by:  Papers (5)  |  Patents (5)
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    This paper presents a procedure for using integrals to solve nonlinear magnetostatic field problems. An integral equation on magnetized volume, expressed in terms of magnetic field H or magnetization M, is discretized by means of edge elements on a tetrahedral mesh and solved numerically by means of a collocation method. The procedure approaches nonlinear by means of the fixed-point iterative technique. It sets up two different iterative schemes with complementary features. This paper gives details about implementation and presents and discusses results on some test cases View full abstract»

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  • Temperature variation of magnetic aftereffect

    Publication Year: 2001 , Page(s): 1118 - 1122
    Cited by:  Papers (10)
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    The paper analyzes the anomalous behavior of the magnetic aftereffect decay coefficient with temperature, which has been established experimentally from a thermodynamic point of view. The Arrhenius law, which has often been used to model magnetic aftereffect, is based on the Maxwell-Boltzmann (MB) statistics. At low temperatures, however, magnons obey Bose-Einstein (BE) statistics, which have a different energy spectrum. MB statistics are a good approximation to BE statistics in the temperature range in which most devices operate. The variation in temperature, governed by chemical potential that is essentially linear, has a negative slope and is zero below a low but finite temperature. Other explanations for this anomalous behavior would predict an incorrect type of temperature dependence. This new interpretation of magnetic aftereffect may have profound implications on accelerated testing to determine life expectancy of recordings View full abstract»

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  • Reliability of PtMn-based spin valves

    Publication Year: 2001 , Page(s): 1123 - 1131
    Cited by:  Papers (7)
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    This paper addresses the lifetime characteristics of standard and synthetic spin valves of different PtMn antiferromagnet (AFM) thicknesses and compositions. It shows that loss of magnetoresistance with time at elevated temperature is less pronounced for synthetic structures, for thinner PtMn AFM films exchange-annealed for relatively longer times, and Pt-rich compositions of PtMn. The lifetime temperature Tmax is defined as the maximum operating temperature for the spin valve that results in less than a 10% drop in output for a five-year 50% duty cycle. The generalized prediction of lifetime temperature Tmax from the more usable unblocked ratio (UBR) point on the UBR-versus-temperature curve is complicated by test conditions and initial Hex values. For Hex values and reverse field magnitudes for the sheet film spin valve samples tested here, the tolerable UBR was in the 6-8% range, and Tmax values in the 170°-205°C range. Choosing the correct reverse field for ΔTb measurements was important for synthetic structures because of the interaction between the applied field and the coupling field between the inner and outer pinned layers in the synthetic structure. Finished heads show Tmax values that are lower by 40°-55° for the five-year 50% duty cycle criterion compared to sheet films. This highlights the importance of processing environments, especially in slider fabrication, and imposes a further restriction on the acceptable sheet film tolerable UBR, reducing it to 3-4%. Activation energies from lifetime tests are in the range 2.2 to 2.6 eV for all samples including finished sliders, which indicates that differences in lifetimes are not associated with large variability in the activation energy of depinning within the PtMn system. The time-dependence of magnetic properties such as interlayer coupling (Hilc) and coercivity (Hc) of the free layer is very important and exhibits runaway behavior with time. It must be monitored for deleterious effects View full abstract»

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  • Multi-functional magnetic Barkhausen emission measurement system

    Publication Year: 2001 , Page(s): 1095 - 1099
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (120 KB)  

    Recently, we developed a system making magnetic Barkhausen emission measurements and performing multifunctional analysis of the results for the purposes of material characterization. The organization of this system, together with the procedures incorporated into the software, allows flexible control of applied fields and multivariate analysis of the Barkhausen signal emissions View full abstract»

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  • Rate 8/9 sliding block distance-enhancing code with stationary detector

    Publication Year: 2001 , Page(s): 1168 - 1174
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    A new distance-enhancing code for partial-response magnetic recording channels eliminates most frequent errors, while keeping the two-step code trellis time invariant. Recently, published trellis codes either have lower code rates or result in time-varying trellises with a period of nine, thus requiring a higher complexity of detectors and code synchronization. The new code introduces dependency between code words in order to achieve the same coding constraints as the 8/9 time-varying maximum transition runlength (TMTR) code, with the same code rate, but resulting in a trellis that has a period of 2. This code has been applied to the E2PR4 and a 32-state generalized partial response (GPR) ISI target. The resulting two-step trellises have 14 and 28 states, respectively. Coding gain is demonstrated for both targets in additive white Gaussian noise View full abstract»

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  • Response of RL network with piecewise linear inductance as a magnetic write head model

    Publication Year: 2001 , Page(s): 1137 - 1140
    Cited by:  Patents (2)
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    This paper presents an analytic solution for the transient response of a parallel RL network with piecewise linear inductance. It compares the rise time and zero-crossing pulse compression of the nonlinear network with a corresponding linear network. It shows that there is a rise time and compression improvement in the nonlinear circuit as the amplitude of the input current increases. It provides analytic expressions as well View full abstract»

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  • Experimental characterization of permanent magnets used in periodic structures

    Publication Year: 2001 , Page(s): 1106 - 1109
    Cited by:  Papers (1)
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    In a periodic structure, the magnetic flux density profile of a hybrid undulator depends strongly on the characteristics of its permanent magnets. A simple procedure to select the best permanent magnets for periodic magnetic structures is presented here. We used a very simple apparatus for the magnetic field measurements. We tested this by assembling periodic structure prototypes formed by brick-shaped permanent magnets View full abstract»

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  • Split-type magnetic field generator with wide homogeneous region

    Publication Year: 2001 , Page(s): 1091 - 1094
    Cited by:  Papers (2)
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    This paper discusses the homogeneity of a magnetic field generator for measurement of nuclear magnetic resonance (NMR). It shows that inhomogeneity is caused by an excess number of turns and a discrepancy from the design dimensions. A control circuit consisting of a pair of shim coils and a few Hall elements can improve the homogeneity. With it, a homogeneity of the magnetic field in the split coil of better than ±0.05% over 50 mm was obtained View full abstract»

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  • Growth kinetics in levitated and quenched Nd-Fe-B alloys

    Publication Year: 2001 , Page(s): 1100 - 1105
    Cited by:  Papers (2)
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    We investigated the growth kinetics and the effect of quenching conditions on rapid solidification of undercooled Nd-Fe-B melts with compositions near the Nd-2-Fe14-B (2-14-1) phase. We prepared melt drops of various undercooling levels (up to 300 K below the liquidus temperature) were prepared by the electromagnetic levitation method and subsequently quenched them onto chill substrates. We measured the solidification kinetics of the undercooled melts in situ using a high-resolution Si photodiode. In accordance with the nucleation theory, the properitectic γ-Fe phase nucleates at first during the undercooling process. There were two different solidification routes, with the observed route depending on the undercooling level of the levitated melt prior to quenching. The peritectic reaction is favored in melts with high undercooling levels prior to quenching. Low previous undercooling levels lead to primary solidification of the 2-14-1 phase on quenching. The thickness of the homogeneous 2-14-1 phase zone, grown directly at the substrate side, depends strongly on the undercooling level prior to solidification. We estimated the growth velocity of the 2-14-1 phase from temperature-time-characteristics to be of the order of 1 mm/s. These investigations give rise to improved understanding about the high sensitivity of the microstructure of Nd-Fe-B alloys on different rapid solidification procedures View full abstract»

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  • Thermal modeling of magnetoresistive heads in three dimensions

    Publication Year: 2001 , Page(s): 1132 - 1136
    Cited by:  Papers (6)
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    We present an analytical model that can describe the dissipation of thermal energy generated by Joule heating in magnetoresistive heads. The model is simple in that it requires no finite-element analysis and can be quickly configured to investigate the effects of varying head characteristics. However, despite its simplicity, the model can quantify heat transfer through all surfaces of the sensor effectively, as demonstrated by comparison with experimental data. With this model, the effects of varying system geometry, materials, bias current, environment, and defects can be investigated, Analysis of these effects identifies parameters to which Joule heating is most sensitive. We discuss promising areas for device improvement, such as increasing the gap thermal conductivity and decreasing contact resistance at interfaces View full abstract»

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  • Detection signal-to-noise ratio versus bit cell aspect ratio at high areal densities

    Publication Year: 2001 , Page(s): 1157 - 1167
    Cited by:  Papers (8)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    As areal density in hard drives increases, the bit aspect ratio (BAR) becomes an increasingly critical design issue. In this paper, we use the detection signal-to-noise ratio (SNR) as a system-level indicator to establish the relationship between the optimal BAR and all major recording system parameters that relate to the head/medium combination and servo as well as the read channel. We address practical and fundamental issues including thermal stability, medium and additive system noise, and equalization and track misregistration. The results of our analysis generally agree with the recent consensus to move toward lower BARs but also caution that the optimal BAR is a strong function of the servo capability. The results of our BAR analysis also indicate that at high areal densities, the ratio of PW50 to the bit cell is considerably smaller than found in today's drives View full abstract»

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  • Dual FDTS/DF: a unified approach to dual-detection and modification for MTR codes

    Publication Year: 2001 , Page(s): 1175 - 1186
    Cited by:  Papers (1)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    Dual-detector decision-feedback schemes have recently gained considerable interest in magnetic recording. Schemes such as dual decision feedback equalization (DDFE), M2DFE, and dual FDTS/DF are dual-detector versions of DFE, multilevel DFE (MDFE), and fixed delay tree search with decision feedback fixed-delay tree search with decision feedback (FDTS/DF) detectors, respectively. At high recording densities, the dual-detector versions significantly improve bit-error-rate (BER) performance and reduce error propagation. In this paper, we first give a unified approach to the bit-error-rate analysis of dual-detector decision feedback schemes in an attempt to highlight their relationship, and then we show that the performance of dual FDTS/DF reduces to that of DDFE for τ=0 and reduces to that of M2DFE for τ=1 with d=1 code constraint. Further, we extend the dual FDTS/DF detection scheme to maximum transition run-length (MTR) coded channels. On the basis of both BER and error event analysis, we propose a modified dual FDTS/DF detection scheme for MTR-coded channels that improves BER performance. The new scheme modifies certain bits in the detection profess for preventing the dominant error event. Simulation results on 6/7 MTR-coded Lorentzian channel show that the modified detector gives around 1 dB SNR improvement over the advanced (trellis-coded extended partial response) TC-E2PR detector View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Meet Our Editors

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