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Magnetics, IEEE Transactions on

Issue 11 • Date Nov. 2012

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Displaying Results 1 - 25 of 504
  • Front cover

    Page(s): C1
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  • IEEE Transactions on Magnetics publication information

    Page(s): C2
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  • Table of contents

    Page(s): 2697 - 2733
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  • Intermag Conference 2012 Conference Chair's Foreword

    Page(s): 2734
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  • Intermag Conference 2012 Publication Chair's Preface

    Page(s): 2735
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  • Intermag Conference 2012 Committee

    Page(s): 2736 - 2738
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  • Spin-Based MOSFETs for Logic and Memory Applications and Spin Accumulation Signals in CoFe/Tunnel Barrier/SOI Devices

    Page(s): 2739 - 2745
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1156 KB) |  | HTML iconHTML  

    New innovative ferromagnetic source/drain technologies on Si for next-generation-transistor applications are researched and developed using CoFe/AlOxn+-Si and CoFe/MgO n+-Si junctions. As evidence of the spin accumulation in the n+-Si conduction channels, nonlocal spin signals and four-terminal nonlocal-Hanle signals are presented for CoFe/MgO/SOI devices. The spin diffusion times determined by four-terminal nonlocal-Hanle signals are consistent with those observed in three-terminal Hanle signals. The relatively long spin diffusion time of τs=1.4 nsec and relatively large spin polarization P=0.43 at room temperature for CoFe/MgO/SOI devices were observed, when fitting to the existing diffusion model for spin injection and accumulation. We have observed the marked enhancement of the absolute value of three-terminal voltage changes via Hanle-type spin precessions (|ΔV|) as a function of interface resistance in the temperature range between 20 K and 300 K. We also have observed the asymmetric bias voltage dependence on ΔV. In terms of the reason of marked enhancement of |ΔV| as a function of interface resistance, the spin absorption into ferromagnet would be most effective. For the explanation of the asymmetric bias voltage dependence, we should take into account two additional possible origins. Moreover, we succeed in decreasing the interface resistance for CoFe/MgO/ n+-Si junctions down to 36 Ωμm2 by using evaporation method for MgO deposition. View full abstract»

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  • Intergranular Exchange Coupling in FePt:X:FePt ( {\rm X}={\rm B} , C, {\rm SiO}_{\rm x} , Cr and {\rm TaO}_{\rm x} ) Thin Films for Heat Assisted Magnetic Recording

    Page(s): 2746 - 2748
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (911 KB) |  | HTML iconHTML  

    In this study we quantitatively determined the exchange coupling across B, C, SiOx, Cr and TaOx segregants by measuring the exchange coupling between two FePt layers separated by segregant layers of varying thickness. Our study indicates that the segregant that provides the best exchange break is TaOx; whereas, C is the worst and SiOx, Cr and B are in between. Our data indicates that a segregant intergranular region thicker than 0.8 nm should decouple FePt grains if B, TaOx, SiOx, or Cr are used, but with C, a thickness greater than 1 nm is required. View full abstract»

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  • An X-Ray Diffraction-Based Method for Evaluating Inhomogeneous Ordering at the Grain Level of {\rm L}1_{0}-{\rm FePt} Media

    Page(s): 2749 - 2752
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    A technique based on x-ray diffraction (XRD) is introduced to understand the variation of the grain-to-grain L10 ordering in FePt recording media. We classify the possible ways that the grains may be ordered into three types: homogeneous ordering, inhomogeneous ordering, and bipolar ordering. We study the possible impact of each type of ordering on the XRD spectra in terms of the relative angular positions of the FePt (001) and (002) peaks. XRD peak profile fitting is carried out to identify the grain ordering type in FePt-SiOx thin films sputtered with in-situ heating. View full abstract»

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  • First-Order Reversal Curve Investigations on the Effects of Ion Implantation in Magnetic Media

    Page(s): 2753 - 2756
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB) |  | HTML iconHTML  

    Ion implantation of different ion species of varying mass on magnetic recording media was investigated. Except for helium (4He+) and cobalt (59Co+) ions, all the other ions showed reduction in saturation magnetization (Ms). In fact, Ms was reduced to ~ 0 emu/cc at a fluence of 2 × 1016 and 5 × 1016 ions/cm2 for antimony (121Sb+) and argon (40Ar+ ) ions, respectively. First-order reversal curves (FORC) showed a reduction in the switching field and distribution as the fluence of the implanted species increased. In addition, the magnetostatic interactions which were present in the media were found to be overwhelmed by an increase in exchange interaction as fluence increased. It was noticed that the heavier the implanted ion, the lower was the lateral range and straggle. A negative correlation was also observed between the straggle of the implanted species and the increased exchange interaction. This observation is expected to play a very crucial role in high-density patterned media fabrication. View full abstract»

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  • Integration of Servo and High Bit Aspect Ratio Data Patterns on Nanoimprint Templates for Patterned Media

    Page(s): 2757 - 2760
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2089 KB) |  | HTML iconHTML  

    Magnetic recording bit patterned media (BPM) stands as a promising technology to deliver thermally stable magnetic storage at densities beyond 1 Tb/in2. High throughput BPM fabrication will be enabled by nanoimprint lithography which relies on a high-quality master template to be able to meet pattern fidelity and low defectivity specifications. Master template fabrication for BPM can be done by e-beam lithography alone or by e-beam directed self-assembly of block copolymers. Incorporating servo features in the fabrication of master templates brings numerous nanofabrication challenges that vary depending on which method is used. Here we demonstrate the fabrication of conventional servo features at 200 Gd/in2 using e-beam lithography and we explore some nonconventional servo geometries that are compatible with self-assembly for BPM beyond 1 Td/in2. View full abstract»

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  • Effects of Device Geometry on Output Circular Polarization in a Spin-LED

    Page(s): 2761 - 2764
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (441 KB) |  | HTML iconHTML  

    A surface emitting spin-polarized light emitting diode (Spin-LED) is considered for the study of the device geometry dependence of the output circular polarization It is found that the output circular polarization is maximum at the outer region of the circular non-FM Ohmic contact to the p-region, which delineates radial extent of the active region in the intrinsic layer. We observe that the output circular polarization increase as a function of the p-contact radius when the contact size is small but for large values of the p-contact radius the reverse trend is noted. An enhancement of the spin diffusion length increases the degree of polarization of the emitted circular light. The enhancement however is observed to fall off for still higher values of spin lifetime. View full abstract»

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  • Transition From GMR to AMR at the Percolation Threshold in Ferrite-Magnetic Alloy Composites

    Page(s): 2765 - 2768
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1108 KB) |  | HTML iconHTML  

    A thermal spray process has been developed for the deposition of ferrites and highly anisotropic composites of magnetic alloys and ferrites. The critical volume fraction for conduction is at 5 to 10 volumetric percent (vol.%) metal in these thick films as compared to 33 vol.% in isotropic mixtures of spheroidal particles. The low percolation threshold and highly anisotropic transport properties are associated with the unusual microstructure of thermal spray coatings which are composed of lamellar splats stacked one upon the other. By varying the volume fraction of metal in these composites it is possible to drastically change the electrical, magnetic and mechanical properties of these coatings. In the sintered mixture the conductivity increases rapidly when the metal volume fraction reaches about 33 vol.% whereas in the thermal spray coating the conductivity increase occurs at metal fractions of about 2-6 vol.%. The magnetoresistance was measured in the parallel, perpendicular and transverse geometry in each case in fields up to 2 kilogauss. There is a clear and sharp transition from giant magnetoresistance (GMR) (negative ΔR/R) to anisotropic magnetoresistance (AMR) at the percolation threshold in both cases. These results show that the GMR comes from the scattering of weakly exchange coupled spins in the polycrystalline ferrite which can be aligned in high fields decreasing the resistance. The AMR is in the conductive metallic phase and its field dependence is mainly controlled by the shape anisotropy of the disk shaped splats as expected. View full abstract»

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  • Measurements of Complex Magnetic Permeability of Nano-Size \varepsilon -Al _{\rm x} Fe _{2-{\rm x}} O _{3} Powder Materials at Microwave and Millimeter Wavelengths

    Page(s): 2769 - 2772
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (617 KB) |  | HTML iconHTML  

    The imaginary part of complex magnetic permeability spectrum confirms the strong ferromagnetic resonance absorptions to appear at 89 GHz for the ε-AlxFe2-xO3 nanomagnets prepared by sol-gel techniques for the x value to be 0.66. A strong anomalous dispersion corresponding to 89 GHz resonance is also observed in the real part of magnetic permeability spectrum. The free space quasi-optical spectrometer equipped with a set of tunable backward-wave oscillators as power sources is used in this work to study the transmittance, real and imaginary parts of complex dielectric permittivity and real and imaginary parts of complex magnetic permeability properties of this nano magnet materials. Complex dielectric permittivity and Complex magnetic permeability spectra over six waveguide bands are almost flat in the 8-40 GHz range The vector network analyzer and in-waveguide measurements were employed for the measurements over 8-40 GHz range. The absorption property is suggested to be caused by the natural resonance achieved by the large magnetic anisotropies in this series of aluminum substituted ferrite nanomagnets. The absorption peak shifts to the lower frequencies with increasing value of x -parameter. The average particle size of ε-AlxFe2-xO3 nanomagnets lies between 25 to 50 nm. The absorption and dispersion characteristics are repeatable for the same density of the powder material. View full abstract»

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  • Microwave and Millimeter Wave Ferromagnetic Absorption of Nanoferrites

    Page(s): 2773 - 2776
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (877 KB) |  | HTML iconHTML  

    Complex dielectric permittivity and magnetic permeability of several commercially available nanoferrites have been studied over a broad microwave and millimeter wave frequency range. Nano-sized barium, strontium, copper, zinc, nickel substituted iron oxide powders with different lattice structures are investigated. A transmission-reflection based in-waveguide technique that employs a vector network analyzer was used to determine the scattering parameters for each sample in two microwave bands (18-40 GHz). A free space quasi-optical spectrometer energized by backward wave oscillators was used to acquire the transmittance spectra in the millimeter wave frequency range (30-120 GHz). Relatively broad and sharp ferromagnetic resonance of hexagonal barium ferrite and strontium ferrite are observed in millimeter wave frequency range. The ferromagnetic resonance peak for nano-sized hexagonal ferrite powder material moves to lower frequencies compared to micro-sized and solid hexagonal ferrites. An X-ray diffraction measurement is performed on these hexagonal ferrites to understand the magnetic behavior and the structure. View full abstract»

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  • Characterization of Organic Thin Films on Ferromagnetic Substrates by Spectroscopic Ellipsometry and Magneto-Optical Kerr Effect Spectroscopy

    Page(s): 2777 - 2780
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (598 KB) |  | HTML iconHTML  

    We report the characterization of metal-phthalocyanine (CuPc and CoPc) thin films prepared on magnetic substrates by spectroscopic ellipsometry (SE) and magneto-optical Kerr effect (MOKE) spectroscopy. CuPc films were prepared on lanthanum strontium manganite (LSMO) substrates while CoPc was deposited onto Co/Pt layer systems. We address the challenge to distinguish between the dominating magneto-optical response of the magnetic substrate and the contribution of the phthalocyanine layers. The procedure is demonstrated for CuPc on LSMO and also applied to CoPc on Co/Pt. The resulting spectral contribution of the organic films is compared to modeled spectra deduced from optical model calculations based on data previously obtained from phthalocyanines on silicon substrates. For CoPc on Co/Pt the average tilt angle of the molecular plane with respect to the substrate plane is estimated to be 73 ° from the ellipsometry data evaluation. View full abstract»

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  • A Novel and Fast Numerical Technique for Large-Scale Electromagnetic Imaging Systems

    Page(s): 2781 - 2784
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    The safety of complex engineered systems and critical infrastructures are important to ensure society's industrial and economic prosperity, advances in complex systems computation and modeling is always greatly desired. Challenges still remain in applications such as large-scale sensing and monitoring of those systems to ensure the structural heath. This paper proposed a novel and fast imaging and modeling mechanism using an optimized fast multipole method with accelerated Cartesian expansion that can significantly reduce the electromagnetic (EM) field calculation, data acquisition and analysis time. Two examples were discussed including defect sensing and a rigorous derivation of error bound in EM imaging. New formulations to simplify the Green's function, the Generalized Maxwell Expansion were also introduced and implemented. View full abstract»

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  • Interactions Between Magnetic Layers Lying Between Soft Boundary Layers

    Page(s): 2785 - 2788
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    Analytic expressions are derived in the 2D frequency-domain for the interaction between magnetized layers that lie between two sheets of soft magnetic material. For example, in writing and reading with perpendicular magnetic recording, a multilayer `hard' magnetic medium lies between the soft magnetic underlayer (SUL) of the medium and the soft structures (including shields) that form the read and write heads. The expression for the interaction between different layers is an extension of earlier work, however the derivation of the self-interaction of a single layer is novel as is the translation of these interactions into tensor form in Cartesian coordinates suitable for micromagnetic modeling. View full abstract»

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  • A Micromagnetic Solver for Large-Scale Patterned Media Based on Non-Structured Meshing

    Page(s): 2789 - 2792
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (948 KB) |  | HTML iconHTML  

    The paper presents a micromagnetic solver, where the long-range contributions to the magnetostatic field are computed by a multipole expansion technique and the spatial distribution of the exchange field is reconstructed via a finite difference scheme able to handle non-structured meshes. In this way, large samples having complex geometries can be simulated. The numerical accuracy, the computational efficiency and the flexibility of the proposed solver are investigated by comparison to standard approaches. View full abstract»

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  • Understanding the Magnetization Reversal in Six-Fold Anisotropic Hexagonal Networks

    Page(s): 2793 - 2796
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (555 KB) |  | HTML iconHTML  

    Isolated magnetic nanowires have been studied extensively and the magnetization reversal mechanism is well understood in these systems. But when these nanowires are joined together in different architectures, they behave differently and can give novel properties. Using this approach, one can engineer the network architectures to get artificial anisotropy. Here, we report six-fold anisotropy by joining the magnetic nanowires into hexagonal network. For this study, we also benchmark the widely used micromagnetic packages: OOMMF, Nmag, and LLG-simulator. Further, we propose a local hysteresis method by post processing the spatial magnetization information. With this approach we obtained the hysteresis of nanowires to understand the six-fold anisotropy and the reversal mechanism within the hexagonal networks. View full abstract»

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  • Reducing Dy Content by Y Substitution in Nanocomposite NdFeB Alloys With Enhanced Magnetic Properties and Thermal Stability

    Page(s): 2797 - 2799
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    Dy has been employed as an additive in NdFeB magnets to improve their coercivity and thermal stability, but the high cost of the Dy has become a major concern. In this work, the effects of Y substitution for Dy on the magnetic properties and thermal stability of melt-spun nanocomposite [Nd0.8(Dy1-xYx)0.2]10Fe84B6 alloys have been systematically studied. The results show that Y substituting Dy can not only improve the remanence and energy product but also improve their thermal stability. [Nd0.8(Dy0.5Y0.5)0.2]10Fe84B6 alloy with 50% Dy reduction exhibits a high maximum energy product of 139 kJ/m3 and low absolute values of temperature coefficients α and β, -0.090%/°C and -0.394%/°C, respectively. It is suggested that Y substitution be a feasible way to reduce the cost of the NdFeB magnets and maintain their high temperature performance. View full abstract»

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  • Anisotropic Nd _{2} Fe _{14} B Submicron Flakes by Non-Surfactant-Assisted High Energy Ball Milling

    Page(s): 2800 - 2803
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    This paper reports on the formation mechanism, structure, crystallographic anisotropy, magnetic properties and postannealing of single-crystal and [001] textured poly-nanocrystalline Nd2Fe14B flakes with a micron, submicron or nanosize thickness prepared by a non-surfactant-assisted high energy ball milling (HEBM) technique. Nd15.5Fe78.5B6 ingot micro-powders were the precursor while ethanol was the only milling medium. Similar to the structural evolution process in the surfactant-assisted HEBM, single-crystal flakes with a micron then submicron thickness were first formed. With further milling, [001] textured poly-nanocrystalline flakes with a submicron then nanosize thickness were formed. The formation of anisotropic flakes was mainly related to the polar nature of ethanol which would form a thin coating layer on the flakes through carboxylate bonds to prevent cold welding and agglomeration during the HEBM. The Nd 2Fe14B flakes prepared by the HEBM in ethanol for 5 h have a [001]-in-plane texture, a thickness in the range of 100-450 nm and a width in the range of 0.7-18 μ m, a coercivity iHc of 2.3 kOe, and a I006/I105 value of Nd2Fe14 B phase of 5.3. Postannealing at 400-550° C for 0.5 h had little effect on the flake dimensions while resulting in a reduced [001] texture and reduced remanence values besides coarser grain sizes. With increasing annealing temperature, iHc first increased, reached its maximum value of 2.8 kOe at 450 °C, then decreased. An anisotropic magnetic behavior was found in all of the as-milled and annealed flakes. View full abstract»

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  • Magnetic Reversal Observation in Nano-Crystalline Nd-Fe-B Magnet by SANS

    Page(s): 2804 - 2807
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    Spin-polarized small-angle neutron scattering (Pol-SANS) measurements for nano-crystalline Nd-Fe-B magnet have been performed in order to clarify the magnetic reversal behavior. Due to high transparency of neutron beam, magnetic and nuclear microstructures in the `bulk' can be observed by SANS. Obtained SANS patterns arising from magnetic domain changes were analyzed by Teubner-Stray model, phenomenological correlation length model, to quantify the periodicity, density and morphology of magnetic domains. The results indicate that magnetic reversal evolves with magnetic domains which have the similar size of the grains. However, even in nano-crystalline system, single domain grain reversal is not realized. View full abstract»

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  • Annealing Temperature and Co Layer Thickness Dependence of Magnetoresistance Effect for L1_{0} -MnGa/Co/MgO/CoFeB Perpendicular Magnetic Tunnel Junctions

    Page(s): 2808 - 2811
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    The post annealing temperature and Co thickness dependence of tunnel magnetoresistance (TMR) ratio was investigated for L10-MnGa/Co(tCo)/MgO/CoFeB perpendicular magnetic tunnel junctions (MTJs). The MnGa/MgO interface optimization by Co insertion was shown to be an effective way for improving the TMR ratio. The TMR value increases with the annealing temperature (Ta), and exhibits maxima at 325 °C for tCo = 1.0 - 5.0 nm. Thermal annealing process improves the structure of MTJs, but also causes elements diffusion. In this work, the annealing effect on MTJs with different Co thicknesses was discussed in detail along with a fast annealing method. View full abstract»

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  • Magnetic Properties and Magnetic Domain Structures Evolution Modulated by CoFeB Layer in [Pd/Co]/CoFeB/MgO/CoFeB/[Co/Pd] Perpendicular MTJ Films

    Page(s): 2812 - 2815
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (732 KB) |  | HTML iconHTML  

    A series of MgO perpendicular magnetic tunneling junction (p-MTJ) films with soft/hard composite electrodes is prepared by RF-sputtering, where amorphous CoFeB is chosen as soft layer. The modulation of MTJs film magnetic properties on CoFeB thickness is investigated. The critical thickness for composite free layer transform from rigid magnet (RM) to exchange spring system (ES) is indentified. Besides, an unexpected in-plane exchange bias is observed which is attributed to the formation of closure domains. The evolution of domain structures on CoFeB is examined by magnetic force microscope. Coexistence of two distinguished magnetic domains of different sizes is observed. It is found that the evolution of domain morphology as varying CoFeB thickness is due to the modulation of effective anisotropy. 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