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Magnetics, IEEE Transactions on

Issue 4  Part 1 • Date July 1998

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Displaying Results 1 - 25 of 434
  • Competition between direct exchange and indirect RKKY coupling in Fe/V[001] superlattices

    Page(s): 864 - 866
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    Fe 10 Å /V tV (001) superlattices are prepared by magnetron sputter deposition and characterized using x-ray diffraction (XRD), magneto-optical Kerr effect (MOKE) magnetometry, and x-ray magnetic circular dichroism (XMCD). MOKE loops show three peaks in saturation field as a function of tV, indicating RKKY induced AF coupling at tV =22 Å, 32 Å, and 42 Å. The expected AF coupling peak at 12 Å, however, is missing. XMCD measurements show that the V layers carry a relatively large magentic moment which extends surprisingly far from the Fe/V interface. Such 'transient ferromagentism' suggests a strong V-V direct exchange coupling within the V layer. We argue that the V-V direct exchange coupling suppresses the 12 Å AF coupling peak, but since direct exchange coupling decays more quickly than RKKY coupling, the AF peaks at 22, 32, and 42 Å are observed. View full abstract»

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  • Magnetic anisotropies of Fe/sub n//V/sub m/[001] superlattices determined by ferromagnetic resonance

    Page(s): 873 - 875
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    The temperature-dependent magnetic anisotropies of Fen/Vm(001) superlattices on MgO(OO1) were determined by Ferromagnetic Resonance (FMR). The Fe-layer thickness n ranges between 2 and 4 atomic layers. The shape anisotropy dominates, and the easy-axis of the magnetization of the samples is always in the film plane. The second-order out-of-plane magnetic anisotropy is mainly determined by magnetoelastic effects due to the in-plane lattice expansion of the Fe. The fourth order in-plane anisotropy presents a strong temperature dependence as a result of the competition between a volume part favoring the Fe-[100] and a surface part favoring the Fe[ll0] in-plane direction. A very small stepinduced in-plane uniaxial anisotropy reveals the existence of very-large atomically-flat terraces. This information, in combination with the observation of very narrow FMR-linewidths, indicates the excellent structural quality of our samples. View full abstract»

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  • Highly field sensitive and thermally stable dc magnetron sputtered soft Ni/sub 81/Fe/sub 19//Cu multilayers

    Page(s): 918 - 920
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    Very soft (Hc~lOe), high field sensitivity (0.44%/Oe) and thermally stable giant magneto- resistance (GMR) properties have been demonstrated in planetary DC magnetron sputtered Ni81Fe19/Cu multilayers (MLs) around the well-defined 2nd antiferromagnetic (AF) coupling peak. These magnetic properties are very promising for magnetic head application. X-ray diffraction data and transmission electron microscopy (TEM) images show that the multilayers are high-quality laying structures with coherent interfaces. Most importantly, it was found that these as-deposited samples, with no Fe buffer layer, only exhibit a strong fcc (111) out-of-plane orientation. This is in contrast to the ion-beam deposition case, where GMR effect is strongly correlated to the Ni81Fe19 and Cu (200) crystallite orientation. View full abstract»

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  • Reversible electrodeposition of ultrathin magnetic Co films

    Page(s): 963 - 967
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    Ultrapure preparation conditions equivalent to ultrahigh vacuum conditions of 5 × 10-10 mbar allow the reproducible deposition of magnetic films in the monolayer (ML) range from aqueous electrolytic solutions. We used this cost and time efficient technique to prepare ultrathin CO films on Cu(001) substrates. A unique feature of electrodeposition is its ability to dissolve previously deposited layers. The thickness of deposited films can be adjusted in situ by dissolution without damaging the rest of the film. This might he useful in precisely tailoring film properties, for example in magnetic multilayers. In situ magneto-optical Kerr effect (MOKE) measurements are a simple and efficient tool for such a purpose and provide a thickness resolution of better than 0.2 ML. The magnetic properties and anisotropies of the electrodeposited films as derived from our in situ MOKE measurements are mainly determined by their epitaxial growth on Cu(001). View full abstract»

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  • Modification of effective surface and crystalline anisotropies of Ag/Fe/Ag-[001]-layers by ion implantation

    Page(s): 1033 - 1035
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    The change of the thickness dependent anisotropies of high dose ion-implanted Ag/Fe/Ag-(001)-layers were studied by ferromagnetic resonance. The experimental results are discussed within the frame of a phenomenological model considering implantation induced lattice misfit strains, which are caused by the reduction of the Ag lattice parameter by interface mixed Fe. With additional structural data from x-ray-diffraction the magnetoelastic constant B1 is determined, which agrees well with the bulk value. View full abstract»

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  • Evidence for domain condensation near the ferromagnetic to paramagnetic transition in perpendicularly magnetized, ultrathin Fe/2 ML Ni/W[110] films

    Page(s): 1039 - 1041
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    Ultrathin, fcc Fe/2 ML Ni(111) films were grown on a W(ll0) substrate in UHV by electron beam evaporation. Fe films less than 2.2 ML thick posses a perpendicular moment that does not reorient to an in-plane easy axis below Tc, the temperature of the ferromagnetic to paramagnetic transition. The magnetic susceptibility of the fllms was measured as a function of temperature using the polar Kerr effect. The real part of the susceptibility is large, peaking at well above 100 SI units, and exhibits a simple exponentJal decay over a range of several tens of Kelvin above the temperature TREM where the remanent magnetization disappears. This behavior of the susceptibility is in agreement with that expected from the perpendicularly magnetiaed domnin structure usually identified as a precursor to a spin reorientation transition. No signature of Tc is found in the susceptibility. View full abstract»

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  • Electric field effects on magnetic and optical properties of MnAs/GaAs[001] thin films

    Page(s): 1042 - 1044
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    Effects on magnetic and optical properties of perpendicular electric fields up to 1 MV/m were studied on thin ferromagnetic films of MnAs grown epitaxially on GaAs(001) substrates. Film thicknesses were 20, 50, 100 and 200 nm. With positive electric field corresponding to positive polarity of the MnAs film with respect to the GaAs substrate, it was found that at a field magnitude of 1 MVlm: (a) the magnetizations of the 20 and 50 nm films decreased by 3.5 and 1 percent, respectively, under both positive and negative fields as measured by vibrating sample magnetometry; (b) the magnetooptical Kerr effect (MOKE) of the 20 nm samples decreased by 3.5 percent in negative field but was unchanged by positive field; (c) the index of refraction of the 20 nm films determined by ellipsometry increased by 1 percent in positive field but was unchanged by negative field. No effects were found in thicker films, indicating the observed effects arise from the region of MnAs near the substrate. The MOKE signal of the 20 nm films has a power law dependence on electric field with an exponent of 0.36 with a standard deviation of 0.04. The intensity of the (10-10) x-ray diffraction peak from the ferromagnetic, hexagonal MnAs phase of a 20 nm film decreased by 5 percent in both positive and negative fields of 1 MV/m; however, there was no corresponding increase in the nonmagnetic, orthorhombic phase. View full abstract»

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  • Magnetic easy axis engineering in ultrathin Cu/Co/Cu[110] structures

    Page(s): 1222 - 1224
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    The magneto-optic Kerr effect in-situ has been used to investigate the effects of exposing ultrathin Co/Cu(llO) films (6ML<30ML) to CO gas and the subsequent effects of depositing submonolayer quantities of Cu. After a given deposition of CO, the adsorption of CO gas (but, not O2, H2) is found to cause the magnetic easy axis to switch 90° from the [00l] to the [1-10] direction. The deposition of submonolayer Cu overlayers are observed to reverse the effect of the adsorbed CO thereby switching the easy axis back to [00l]. For thin CO films (dCo<15ML), Cu overlayers switch the magnetic easy axis back to the [00l] direction abruptly. In thicker CO films (>15ML) the easy axis is found to shift gradually from the [l-10] to the [00l] direction, and it allows us to controllably engineer the direction of the magnetic easy axis at a constant CO thickness. View full abstract»

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  • Conference Author Index

    Page(s): 2165 - 2172
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    Freely Available from IEEE
  • Variation of the heat flux between a slider and air bearing when the slider flies over an asperity

    Page(s): 1705 - 1707
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    A quasi steady heat transfer model is introduced to study the mechanism of the variation of the heat flux between a slider and air bearing when the slider flies over an asperity without contact. The simulation results show that the heat flux is related to the air bearing spacing. When a slider flies over an asperity, its flying height fluctuates, which causes the air bearing spacing to fluctuate, and this in turn causes the heat flux between the slider and the air bearing to fluctuate. Corresponding to a decrease of the flying height, the heat flux out of the slider increases and vice versa. The variation of the heat flux causes a variation of the temperature of the Magnetoresistive (MR) transducer, and therefore a variation of the amplitude of the read-back signal View full abstract»

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  • Characteristics of AP bias in spin valve memory elements

    Page(s): 1063 - 1065
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    Spin valve memory element biased with a pair of antiparallel (AP) coupled ferromagnetic layer was analyzed and modeled via micromagnetic simulation. In an AP structure, an external field results in a torque, causing the antiparallel magnetization (AP) axis to rotate towards the direction orthogonal to the field. In addition, due to its strength difference between the two AP layers, the magnetostatic field from the free layer of the spin valve can lead to irreversible AP axis flipping. This irreversible flipping can be effectively prevented by applying an AF/F exchange pinning to one of the AP layers to overcome the differential field from the free layer View full abstract»

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  • Nucleation of periodic domain structure in micro-fabricated spin valve strip pattern

    Page(s): 1072 - 1074
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    Local magnetization reversal in a lithographically fabricated sub-μm spin valve strip has been performed with spatially modulated magnetic fields, produced by overlaid parallel conductor lines with 5 μm line width and 5 μm separation. Evaporated spin valve of NiFe/Co/Cu/Co was used for the material. Nucleation of periodic domains in the soft magnetic layer was confirmed with the ratio of the current induced MR change to the whole MR change attained with an external field. The critical current densities required for the magnetization reversal were 15 and 23 mA/μm for strips with 0.4 and 0.2 μm width. The current induced magnetic field calculated from the critical current was 50% larger than the external reverse field View full abstract»

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  • Design of high frequency inductors based on magnetic films

    Page(s): 1375 - 1377
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    Magnetically coated stripe inductors with conductor insulated from the magnetic film and with conductor in direct electrical contact with the magnetic film are analyzed. A simple equivalent circuit model shows that for the structure without insulation, regardless of the fact that the dc resistivity of the magnetic film is much higher than that of the conductor, most of the driving current flows in the magnetic film at frequencies where the impedance of the device is dominated by inductance, i.e., where the quality factor Q>1. This effect of current re-distribution significantly lowers the performance of the device. A design is proposed having insulation layers to avoid current flow in the magnetic film, which is broken up in sections along the conductor stripe to avoid displacement currents in the system View full abstract»

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  • Tribology in ultra-high density tape drive systems: State of the art and future challenges

    Page(s): 1883 - 1888
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    Advanced ultra-high density tape drives require ever increasing volumetric recording densities which places a premium on the tribology of the head-to-tape interface. For these drives, ultrathin smooth tapes would be in contact or near contact with the recording head at high relative velocities. Minimum friction, near zero wear with stable magnetic performance over a wide range of operating conditions is required for adequate performance. There are considerable tribological challenges related to both recording heads and media to be used in these systems. Some of the many challenges in the design of these drives are: attaining low air bearing surface wear, attaining and maintaining low pole tip recession, developing durable tape media, and developing dimensionally stable substrates with high modulus for ultra-thin tapes View full abstract»

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  • A new nonlinear multi-filter detection concept for the high density magnetic recording channel

    Page(s): 1934 - 1936
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    In this work, a new approach to detection in high density magnetic recording is presented. The basic detector structure is a bank of parallel sub-detectors which are specialized in different channel states. The individual adaptation of the sub-detectors to the channel properties is done by a learning algorithm so that no explicit channel model is required. On both simulated and experimental data it is shown that the proposed detection scheme has excellent performance in the presence of strong nonlinear distortion and signal dependent noise. At user densities of 3.5 and 4.0 using RLL(1,7) encoding the new scheme outperforms multi-level decision feedback equalization (MDFE) detection by a factor of up to 500 in error rate. The structure is well suited for hardware implementation View full abstract»

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  • An analysis of frame formats for digital tape recording

    Page(s): 1940 - 1942
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    In this paper, an analysis technique is presented for block oriented data formats in digital tape recording systems. The approach determines format parameters that maximize the information storage density at a specified failure rate. In the process, it is also shown that block interleaving is not beneficial for many systems View full abstract»

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  • Domain structures supported by micron-sized patterned Co/Cu multilayers with AF and FM coupling

    Page(s): 1012 - 1014
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    Micron-sized Co/Cu multilayer elements were prepared by dc magnetron sputtering and subsequent lift-off patterning. Two types of patterned multilayers, AF or PM coupled, were produced by controlling the width of the Cu spacer layers. Domain structures supported by these elements during magnetic switching have been imaged directly using the Lorentz imaging mode, differential phase contrast, in TEM. Patterning of the FM coupled multilayers introduces significant differences in the domain structures observed in the films as they adopt flux closure geometries in the remanent state. For AF-coupled multilayers little change occurs View full abstract»

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  • Self-assembly in model magnetic inks

    Page(s): 1687 - 1689
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    We have studied the stability of ordered structures in simulated suspensions of magnetic particles similar to those used in the manufacture of magnetic tape. We previously reported (1997) that a monodisperse colloidal suspension of acicular uniformly magnetized particles forms a smectic ordered phase consisting of planar layers within which the particles are oriented perpendicular to the plane. One reason why these structures have not been seen experimentally may be that real magnetic inks have a distribution of particle sizes. We have generalized the simulation to allow this, using a log-normal length distribution. We find that the smectic structure is stable against a small amount of polydispersity-a system of particles with a 10% length variation forms a smectic structure similar to the monodisperse system, whereas 25% variation is sufficient to suppress the ordering. Work is under way to quantitatively establish the phase boundaries for the smectic ordering View full abstract»

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  • An analytical method of a planar parametric transformer based on the magnetic circuit model

    Page(s): 1354 - 1356
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    A planar parametric transformer (5 mm×7 mm size) has various desirable features including excellent voltage regulation, overload protection, and noise rejection. In this paper, the no load performance of the parametric transformer is analyzed. A nonlinear second-order differential equation with time-varying coefficients is set up from the parametric oscillation circuit, and is solved by the harmonic balance method. The calculated values agreed approximately with the experimental ones View full abstract»

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  • Finite element simulation of digital recording on ME tape and comparison with experimental data

    Page(s): 1976 - 1978
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    A vector Preisach hysteresis model, taking into account the out-of-plane anisotropy of metal evaporated recording tapes was developed and implemented in a 2D finite element software, so as to model the writing process on these media. The shape of the computed transition is clearly modified by anisotropy. Computed and experimental readback voltages were compared and a very close agreement was found, which can not be achieved by using only a scalar model View full abstract»

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  • Shear mode piezoelectric microactuator for magnetic disk drives

    Page(s): 1910 - 1912
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    We developed a new piezoelectric microactuator for dual-stage actuator systems in magnetic disk drives. This actuator exploits the shear mode of piezoelectric elements and drives the head suspension assembly. This paper describes the structure of our piezoelectric actuator, its mechanical characteristics, and the experimental results of a life test after driving the piezoelectric elements in an atmosphere of high temperature and humidity View full abstract»

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  • Performance of an 8/9 rate matched spectral null code on the PR4 magnetic recording channel

    Page(s): 1943 - 1945
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    The performance of an 8/9 rate matched spectral null (MSN) code is analyzed on the PR4 magnetic recording channel with additive white Gaussian noise (AWGN) at the sensor. The high rate is achieved with a fixed charge constraint code of block length N=27 on each of the PR4 channel's dicode interleaves. A simplified semi-analytic method for MSN codes that approximates the constants multiplying the Q function for certain error event types is introduced and validated by simulations. The 8/9 rate MSN/PR4 system was compared to a normal 16/17 rate code with PR4 and EPR4 detectors for a range of user densities. The MSN/PR4 system has less than 0.9 dB net coding gain for user densities above 2.25, and it's inferior to simple EPR4 at user densities above 1.9 View full abstract»

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  • Spin-valves with bias compensation layer

    Page(s): 1498 - 1500
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    We successfully used a bias compensation layer (BCL) for an improved bias state and asymmetry in spin-valves having a structure of Ta/NiFe/Pd32Pt17Mn/CoFeB2/Cu/CoFeB 2/NiFe/Ta/BCL/Ta. The shift of an MR response curve from a zero field is almost zero regardless of the polarity and magnitude of the sense current in an unshielded spin-valve element. Inductive/spin-valve heads were fabricated having trimmed high-Bs electroplated Ni45Fe55 top poles and a Ta(50 Å)/NiFe(20 Å)/PdPtMn(200 Å)/CoFeB(20 Å)/Cu(28 Å)/CoFeB(25 Å)/NiFe(20 Å)/Ta(100 Å)/NiFe(30 Å)/Ta spin-valve film. Their read/write performance was tested on a CoCr19Pt5Ta2Nb2 thin-film disk. The dependence of sense current on the asymmetry was small. Narrow, effective write and read track widths of 0.85 μm and 0.62 μm were measured, an output of 660 μVpp and D50 of 200 kFCI were obtained View full abstract»

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  • Magnetic readback microscopy applied to laser-texture characterization in standard desktop disk drives

    Page(s): 1777 - 1779
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    We present a variant of the magnetic-readback microscopy (MRM) technique that provides an electronic “window” into a sealed hard-drive. The analog read-back signal is probed at the preamplifier test points and is demodulated to provide local average amplitude versus time data. This data is captured repeatedly as the head is stepped by the drive servo in fractional track increments. The result looks rather like atomic force microscopy, except that the head itself is the sensing element, Z-axis sensitivity down to 2 nm and lateral resolution of the order of 1 μm can be achieved. Modified firmware of an existing disk drive allowed full servo-control in the landing zone. This was necessary to study the laser texture with the Magnetic Readback Microscope (MRM). In a sealed drive, laser-bump shape, pitch and height can be measured. We further demonstrate a technique to measure the Laser bump arrangement within the drive. We also include a comparison between MRM and Thermal Proximity Mapping (TPM) on laser bumps and thermal asperities. Finally, we report variations in Mrt caused by the laser bump annealing during certain disk manufacturing processes View full abstract»

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  • Fabrication, micromagnetic and recording properties of CoCrPt on plastic disks

    Page(s): 1594 - 1596
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    CoCrPt media with 20 nm thickness are fabricated at low temperatures on plastic disks using Cr and SiO2 underlayers and on glass substrates using a Cr underlayer. The fabrication condition is optimized for high coercivity of 2.2 kOe on plastic and 2.4 kOe on glass. The dependence of magnetic properties on Ar pressure and sputtering power of CoCrPt is discussed for the media an plastic disks in comparison with the glass case. The micromagnetic properties such as Barkhausen volume and δM are discussed. Recording properties of the media on plastic disks deposited under different fabrication conditions are also discussed, and are found to be consistent with micromagnetic properties 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