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David J. Sellmyer - One of the best experts on this subject based on the ideXlab platform.

  • novel nanostructured rare earth free magnetic materials with high Energy Products
    Advanced Materials, 2013
    Co-Authors: Balamurugan Balasubramanian, Ralph Skomski, Bhaskar Das, Wenyong Zhang, David J. Sellmyer
    Abstract:

    Novel nanostructured Zr2 Co11 -based magnetic materials are fabricated in a single step process using cluster-deposition method. The composition, atomic ordering, and spin structure are precisely controlled to achieve a substantial magnetic remanence and coercivity, as well as the highest Energy Product for non-rare-earth and Pt-free permanent-magnet alloys.

  • high Energy Product exchange spring fept fe cluster nanocomposite permanent magnets
    Journal of Magnetism and Magnetic Materials, 2006
    Co-Authors: X Rui, David J. Sellmyer, Zhiguang Sun, Jeffrey E Shield, Lanping Yue, Z Liu, D J Miller
    Abstract:

    Abstract In this paper, we report on the Production of Fe cluster/FePt matrix nanocomposite permanent magnets. Monodispersed Fe clusters with sizes below 10 nm were formed by gas aggregation techniques. These Fe clusters were imbedded in an FePt matrix by alternate deposition from two sources. Specimens with a range of Fe cluster phase content from 0 to 30 vol% were produced by controlling deposition times from each source. As-deposited FePt formed in the A1 structure; thus, post-deposition heat treatment was necessary to form the hard magnetic L10 FePt compound. A single-step heat treatment at 600 °C for 10 min leads to nanocomposite structures with excellent magnetic properties. The coercivity decreased with increasing Fe cluster content, while the Energy Product initially increased, reaching a maximum of almost 18 MGOe, and then decreased at higher Fe cluster content. Secondary heat treatment at 500 °C significantly improved the magnetic properties when compared with the single-step heat treatment at 600 °C. Increased coercivity and remanence was observed, resulting in Energy Products of 21 MGOe. The Energy Products are close to 70 percent greater than expected for uncoupled systems.

  • in cluster structured exchange coupled magnets with high Energy densities
    Applied Physics Letters, 2006
    Co-Authors: X Rui, Zhiguang Sun, Jeffrey E Shield, David J. Sellmyer
    Abstract:

    In this letter, the authors demonstrate isotropic Fe–Pt exchange-spring nanocomposite permanent magnets with a soft magnetic phase fraction of greater than 0.5 with a coercivity of 6.5kOe, single-phase-like magnetic behavior, and an Energy Product of 25.1MGOe. Sub-10-nm Fe–Pt clusters are formed with compositions in the two-phase Fe3Pt and FePt regions. Intracluster structuring on a scale of a few nanometers occurs after appropriate heat treatment. This ensures full exchange coupling between the two phases, allowing greater soft magnetic phase fractions. The results provide insight into developing high Energy Product nanostructured permanent magnets.

  • cluster assembled exchange spring nanocomposite permanent magnets
    Journal of Applied Physics, 2005
    Co-Authors: X Rui, David J. Sellmyer, Zhiguang Sun, Jeffrey E Shield
    Abstract:

    Isotropic nanocomposite magnetic structures were produced via cluster assembly routes with Energy Products reaching 18 MG Oe. Gas aggregation produces Fe clusters with an average size less than 10 nm with a very narrow size distribution, and these were embedded in a hard magnetic matrix by cosputtering of FePt. Structures produced were crystallographically isotropic with Fe cluster phase content ranging from 0 to 30 vol %. The coercivity decreased from 13 kOe as Fe cluster content increased. Single-phase-type hysteresis loops indicating excellent exchange coupling at low Fe cluster content give way to a stepped demagnetization loop at an Fe cluster content greater than 20%. The Energy Product initially increased with Fe cluster content, then decreased.

Oliver Gutfleisch - One of the best experts on this subject based on the ideXlab platform.

  • high Energy Product in battenberg structured magnets
    Applied Physics Letters, 2014
    Co-Authors: S Bance, Oliver Gutfleisch, Harald Oezelt, T Schrefl, Michael Winklhofer, G Hrkac, Gergely T Zimanyi, Richard F L Evans, R W Chantrell
    Abstract:

    Multiphase nano-structured permanent magnets show a high thermal stability of remanence and a high Energy Product while the amount of rare-earth elements is reduced. Non-zero temperature micromagnetic simulations show that a temperature coefficient of remanence of −0.073%/K and that an Energy Product greater than 400 kJ/m3 can be achieved at a temperature of 450 K in a magnet containing around 40 volume percent Fe65Co35 embedded in a hard magnetic matrix.

  • high performance hard magnetic ndfeb thick films for integration into micro electro mechanical systems
    Applied Physics Letters, 2007
    Co-Authors: Nora Dempsey, K. Khlopkov, F. May, Dominique Givord, Arnaud Walther, Oliver Gutfleisch
    Abstract:

    5μm thick NdFeB films have been sputtered onto 100mm Si substrates using high rate sputtering (18μm∕h). Films were deposited at ⩽500°C and then annealed at 750°C for 10min. While films deposited at temperatures up to 450°C have equiaxed grains, the size of which decreases with increasing deposition temperature, the films deposited at 500°C have columnar grains. The out-of-plane remanent magnetization increases with deposition temperature, reaching a maximum value of 1.4T, while the coercivity remains constant at about 1.6T. The maximum Energy Product achieved (400kJ∕m3) is comparable to that of high-quality NdFeB sintered magnets.

  • High performance hard magnetic NdFeB thick films for integration into micro-electro-mechanical systems
    Applied Physics Letters, 2007
    Co-Authors: N M Dempsey, K. Khlopkov, F. May, Dominique Givord, Andreas Walther, Oliver Gutfleisch
    Abstract:

    5$\mu$m thick NdFeB films have been sputtered onto 100 mm Si substrates using high rate sputtering (18 $\mu$m/h). Films were deposited at ≤ 500 C and then annealed at 750 C for 10 minutes. While films deposited at temperatures up to 450 C have equiaxed grains, the size of which decreases with increasing deposition temperature, the films deposited at 500 C have columnar grains. The out-of-plane remanent magnetization increases with deposition temperature, reaching a maximum value of 1.4 T, while the coercivity remains constant at about 1.6 T. The maximum Energy Product achieved (400 kJ/m3) is comparable to that of high-quality NdFeB sintered magnets.

J. M. D. Coey - One of the best experts on this subject based on the ideXlab platform.

  • sm fe n revisited remanence enhancement in melt spun nitroquench material
    Journal of Magnetism and Magnetic Materials, 2019
    Co-Authors: J. M. D. Coey, P Stamenov, S B Porter, M Venkatesan, Rui Zhang, T Iriyama
    Abstract:

    Abstract Following its discovery in the aftermath of Nd2Fe14B, Sm2Fe17N3 seemed to offer intrinsic magnetic properties that were superior or comparable to those of its famous predecessor. But the promise of the new material to challenge Nd2Fe14B was not realized, mainly because the 2:17 nitride powder, prepared by a low-temperature gas-phase interstitial modification process, was unstable at the temperatures needed to process dense sintered magnets. Here we discuss the magnetic properties of Nitroquench, a melt-spun Sm-Fe-N material, which offers superior corrosion resistance and thermal stability compared to melt-spun Nd-Fe-B. The powder, with a crystallite size of approximately 30 nm is in the form of flakes 15–18 µm thick and about 100 µm in diameter. Room-temperature coercivity is 690 kAm−1 after saturation in 14 T, with a remanence of 92 Am2kg−1 and an extrapolated saturation magnetization of 160 Am2kg−1. The remanence enhancement is reflected in a preferred orientation seen in 57Fe Mossbauer spectra of magnetized isotropic powder, which exhibits different relative intensities of the ΔM = 0 absorption lines according to the direction of the field used to saturate the magnetization. When measured in zero internal field, the remanence ratio Mr/Ms is 64%. The remanence enhancement is attributed to a nanocrystallite size that is not very much greater than the exchange length. The maximum Energy Product for the powder, assuming full density, is 162 kJm−3. Nitroquench powder may be used to produce bonded magnets with an Energy Product >100 kJm−3.

  • magnetic anisotropy how much is enough for a permanent magnet
    Scripta Materialia, 2016
    Co-Authors: Ralph Skomski, J. M. D. Coey
    Abstract:

    Abstract Material choices for permanent magnets are analyzed in terms of Energy Product, anisotropy and hardness parameter. Energy Product is the main consideration for permanent magnets, because the purpose of a magnet is to store magnetostatic Energy and create as much flux as possible in the surrounding space. Magnet processing is easiest if the hardness parameter is significantly greater than one. The anisotropy requirement becomes increasingly stringent for large Ms and K1 values of 1 to 2 MJ/m3 may be insufficient. Some potential new magnets and alternative strategies to develop magnetic hardness are discussed.

  • permanent magnets plugging the gap
    Scripta Materialia, 2012
    Co-Authors: J. M. D. Coey
    Abstract:

    Abstract Bulk permanent magnets are indispensable components of numerous consumer and industrial Products for Energy conversion. The market splits roughly 2:1 between Nd–Fe–B and hard ferrite, whose costs are currently in a ratio of more than 25:1. The escalation of rare earth costs presents an opportunity for new magnets with an Energy Product of 100–200 kJ m −3 , intermediate between ferrite ( −3 ) and Nd–Fe–B (>200 kJ m −3 ), provided the costs of raw materials and manufacturing are kept low.

  • nucleation field and Energy Product of aligned two phase magnets progress towards the 1 mj m sup 3 magnet
    IEEE Transactions on Magnetics, 1993
    Co-Authors: Ralph Skomski, J. M. D. Coey
    Abstract:

    The exchange hardening of nanostructured two-phase systems composed of an aligned hard phase and a soft phase with high magnetization is investigated using a micromagnetic approach, which accounts for interactions between the soft regions. For Sm/sub 2/Fe/sub 17/N/sub 3/(2.5 nm)/Fe/sub 65/Co/sub 35/(9 nm) multilayers, an Energy Product as high as 1 MJ/m/sup 3/ (120 MGOe) is predicted, with a rare-earth content of only 5 wt.%. Giant Energy Products may also be achieved in suitable cellular and disordered structures. >

  • Giant Energy Product in nanostructured two-phase magnets
    Physical Review B, 1993
    Co-Authors: Ralph Skomski, J. M. D. Coey
    Abstract:

    Exchange hardening of nanostructured two-phase systems composed of an aligned hard phase and a soft phase with high magnetization is investigated using an approach which yields analytic nucleation fields from the micromagnetic vector equation, and accounts for interactions between the soft regions. In suitable structures the nucleation field is proportional to the volume-averaged anisotropy constant. For example, a multilayer composed of alternating 2.4 nm hard-magnetic Sm2Fe»N3 layers and 9 nm Fe65Co35 layers can have an Energy Product as high as 1 MJ/m' (120 MG Oe), with a rare-earth content of only 5 wt%. Giant Energy Products may also be achieved in suitable cellular and disordered struc- tures.

G P Zhao - One of the best experts on this subject based on the ideXlab platform.

  • interface layer thickness dependence of magnetic properties of smco fe exchange spring multilayers an analytical micromagnetic approach
    Journal of Magnetism and Magnetic Materials, 2020
    Co-Authors: Qian Zhao, F.j. Morvan, Xuefeng Zhang, G P Zhao, Yanli Liu
    Abstract:

    Abstract Experiments have found that the interface layer formed by the interface atomic diffusion in the SmCo/Fe hard/soft exchange-spring system may improve magnetic properties such as the nucleation field and Energy Product. One-dimensional (1D) analytical micromagnetics can well explain the underlying physics of this phenomenon. In this paper, the magnetic properties of SmCo/Fe exchange-spring multilayers are studied by an analytical micromagnetic approach, focusing on the effect of the interface layer thickness on demagnetization progress. The equations for the angular distribution of the magnetization in all layers and the interface constraint are first derived analytically. The microscopic and macroscopic hysteresis loops, the Energy Product and angular distribution are calculated, with realistic values for the interface layer thickness considered. It is found that as the interface layer thickness increases, the nucleation field rises, the coercivity increases first and then is almost constant, hence the maximum Energy Product goes up, while the angular distribution and depinning field decrease. The nucleation field rises with the interface layer thickness for a wide region of the interface exchange Energy constant, calculated by a three-dimensional (3D) micromagnetic software (OOMMF), which agrees perfectly with 1D calculated results. Meanwhile, the nucleation field goes up with the interface exchange coupling coefficient for any interface layer thickness. Above results indicate that the existence of an interface layer between the soft and hard layers enhances the exchange coupling interaction between them, which is qualitatively consistent with the experiment in [Appl. Phys. Lett. 91, 072509 (2007)], as confirmed via an in-plane 1D model with interface layer.

  • the influence of interface anisotropy on demagnetization progress and magnetic properties in parallelly oriented hard soft exchange coupled multilayers
    Journal of Magnetism and Magnetic Materials, 2019
    Co-Authors: Qian Zhao, F.j. Morvan, Xuefeng Zhang, G P Zhao
    Abstract:

    Abstract The effect of the interface anisotropy on the demagnetization progress and magnetic properties in Nd2Fe14B/α-Fe exchange-coupled multilayers with parallel crystalline anisotropy has been investigated within a micromagnetic framework. A set of equations satisfied by the angle between the magnetization and the applied field, as well as the formula for the nucleation field, have been derived analytically. The nucleation field goes up linearly with the interface anisotropy constants varying from −1 erg/cm2 to 1 erg/cm2 in a wide thickness range, with an amplitude up to 13%. The microscopic hysteresis loops, the evolution of the domain walls, the macroscopic demagnetization curves and the Energy Products are given by numerical calculations. The results indicate that the interface anisotropy affects not only the nucleation field and the maximal magnetic Energy Product, but also the pinning field or the coercivity. Positive interface anisotropy evidently enhances the pinning field or the coercivity, however, negative interface anisotropy obviously deteriorates the maximal Energy Product. These results suggest that a positive interface anisotropy should be preferred experimentally.

O P Pandey - One of the best experts on this subject based on the ideXlab platform.