DOCSLIB.ORG

A New Approach for Improving Exchange-Spring Magnets (PDF

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A New Approach for Improving Exchange-Spring Magnets (PDF JOURNAL OF APPLIED PHYSICS 97, 10K311 ͑2005͒ A new approach for improving exchange-spring magnets J. S. Jiang, J. E. Pearson, Z. Y. Liu, B. Kabius, S. Trasobares, D. J. Miller, and S. D. Bader Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 D. R. Lee, D. Haskel, and G. Srajer Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 J. P. Liu Department of Physics, University of Texas at Arlington, Arlington, Texas 76109 ͑Presented on 11 November 2004; published online 13 May 2005͒ It is demonstrated here that an already ideal exchange–spring magnet can be further improved by intermixing the interface. This is counter-intuitive to the general expectation that optimal exchange– spring magnet behavior requires an ideal, atomically coherent soft–hard interface. Epitaxial Sm– Co/Fe thin-film exchange–spring bilayers are thermally processed, by annealing or high-temperature deposition, to induce interdiffusion. With increasing processing temperature, the hysteresis loop becomes more single-phase-like, yet the magnetization remains fully reversible. The interface is characterized via synchrotron x-ray scattering and electron microscopy elemental mapping. The magnetization behavior is modeled by assuming a graded interface where the material parameters vary continuously. The simulations produce demagnetization curves similar to experimental observations. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1855032͔ I. INTRODUCTION moting intermixing of Sm–Co with Fe. The graded interface has a fundamentally different magnetization behavior than a The exchange–spring principle1 identifies a route for cre- sharp interface and relaxes the grain size requirement for ating high-performance permanent magnets from existing optimal exchange–spring properties. materials rather than by an Edisonian search for new mag- netic compounds. In an exchange–spring magnet, nano-scale II. EXPERIMENTAL DETAILS hard and soft magnetic phases are coupled via interfacial exchange interaction such that the soft phase becomes “hard- The Sm–Co/Fe exchange–spring bilayers were fabri- ened” and its high magnetization enhances the energy prod- cated by dc magnetron sputtering. The nominally Sm2Co7 ͑ ͒ ͑ ͒ uct BH max of the composite. While great efforts have been layer was grown epitaxially at 400 °C onto a Cr 211 - expended towards controlling the grain sizes during magnet buffered single crystal MgO͑110͒ substrate to achieve an in- processing, metallurgical approaches such as using nonmag- plane uniaxial anisotropy, as described in Ref. 10. The thick- netic additives come at the expense of forming grain bound- ness of the Sm–Co layer in all samples was kept at 20 nm. ary phases and reducing the overall magnetization.2–4 Con- Following the deposition of the Sm–Co hard layer, a 10 nm- cerns about reduced interfacial coupling due to the grain or 20 nm-thick Fe layer was either deposited at 70–100 °C, boundary phase also led to the notion that optimal exchange– or immediately at 400 °C. All samples were capped with ͑ ͒ ͑ ͒ spring magnets require ideal, atomically coherent soft–hard 10 nm of Ag or Ag 5nm”Cr 5nm cover layers. Pieces interfaces.1,5 However, the soft phase in exchange-springs were cut from the as-deposited samples and were annealed reverse by nucleating a quasi-Bloch wall, and unlike the for one hour at temperatures ranging from 200 to 400 °C, Stoner–Wohlfarth case, the exchange field Hex does not de- using the same heater inside the deposition chamber in a pend very sensitively on the interfacial exchange constant.6 vacuum of 1ϫ10−8 Torr. We denote a sample by its sub- Furthermore, even for an ideal exchange–spring interface, strate temperature TS or annealing temperature TA, which is Hex is finite, determined by the soft phase exchange constant the highest temperature the soft layer was subjected to during and thickness.7 For an exchange spring with 200 Å of Fe as processing. Х the soft phase, Hex 2 kOe. Thus, there exists a fundamental The crystal structure and interfacial morphology of the limit to exchange hardening, and improving the interfacial samples were characterized by x-ray diffraction using Cu K␣ epitaxy does not overcome the limit. radiation and by cross-sectional energy-filtered transmission This limit can, rather counter-intuitively, be circum- electron microscopy ͑EFTEM͒. EFTEM provides the real- vented by intermixing the interface. In this article, we dem- space mapping of different elements from the electron en- ͑ ͒ onstrate the enhancement of the nucleation field HN, and ergy loss spectra EELS at characteristic absorption ener- ͑ ͒ hence BH max, of epitaxial Sm–Co/Fe bilayers by thermal gies, with a spatial resolution of 0.5 nm. We also extracted processing. In contrast to previous studies aimed at interface the interface width and roughness amplitude parameters by modification,8,9 we start with an exchange spring where the fitting both the specular and off-specular reflectivity mea- interface is already ideal, and create a graded interfacial re- sured using synchrotron radiation. The magnetic properties gion where the material parameters vary gradually by pro- were measured at room temperature by tracing the hysteresis 0021-8979/2005/97͑10͒/10K311/3/$22.5097, 10K311-1 © 2005 American Institute of Physics Downloaded 30 Sep 2005 to 164.54.84.133. Redistribution subject to AIP license or copyright, see http://jap.aip.org/jap/copyright.jsp 10K311-2 Jiang et al. J. Appl. Phys. 97, 10K311 ͑2005͒ FIG. 2. ͑a͒ The demagnetization and ͑b͒ the dc demagnetization remanence ͑ ͒ ͑ ͒ curves for Sm–Co 20 nm ”Fe 10 nm samples annealed at various tem- peratures. ͑c͒ The demagnetization and ͑d͒ the dc demagnetization rema- ͑ ͒ ͑ ͒ nence curves calculated for Sm–Co 20 nm ”Fe 10 nm bilayers with inter- facial regions of various thickness. TA =400 °C. The images are constructed from the EELS spectra and color-coded to represent the spatial distribution of the elements Fe, Co, and Cr. The Co map ͑red͒ shows the notch in the TS =100 °C sample due to interfacial roughness, whereas the TA =400 °C sample has a diffuse boundary be- tween the Fe ͑green͒ and Co maps and a notch is blurred out. The difference in interdiffusion in the samples can be seen more clearly in the 9 nm-wide line scans. In the TS =100 °C sample the layers are well-defined, but in the TA =400 °C sample Fe is found in the entire Sm–Co layer while the amount of Co entering into the Fe layer decreases with distance from the interface. Synchrotron reflectivity mea- surements show similar total interface width of ϳ2.5 nm for ͑ ͒ ͑ ͒ FIG. 1. EELS elemental maps and line scans of Sm–Co 20 nm ”Fe 20 nm ͑ ͒ ͑ ͒ both samples, but roughness amplitude of 2.0 nm for the samples with a TS =100 °C and b TA =400 °C. The line scans are taken from the 9 nmϫ90 nm area enclosed by the dashes. ͑c͒ Comparison of the TS =100 °C sample and 0.7 nm for the TA =400 °C sample. high-angle x-ray diffraction of the two samples measured around the High angle x-ray diffraction of the TA =400 °C sample ͑ ¯ ͒ Sm–Co 2200 peak. shows a broad shoulder to the right of the Sm–Co͑22¯00͒ peak. The shoulder could not be fitted with a single Gaussian loops and the dc demagnetization remanence ͑DCD͒ curves curve, suggesting a distribution of phases with smaller lattice using an alternating gradient magnetometer with the field constants. While the EELS elemental maps provide the struc- applied along the easy direction of the Sm–Co layer. For the tural characteristics over the limited field-of-view of DCD curves, the samples were saturated with a +1.4 T field EFTEM, the scattering techniques average over the macro- each time before a demagnetizing field was applied, then the scopic area on the samples illuminated by the x-ray. The remanent magnetization was measured and plotted as a func- consistency among the results from the three techniques tion of the demagnetizing field. proves conclusively that the Sm–Co/Fe interface evolves from being sharp but jagged to smoother and interdiffused upon thermal processing at elevated temperatures. III. RESULTS AND DISCUSSION Shown in Fig. 2͑a͒ are the demagnetization branches of The epitaxial Sm–Co/Fe bilayers are a model exchange– the hysteresis loops for Sm–Co͑20 nm͒ Fe͑10 nm͒ samples 11,12 ” spring system with ideal, coherent interfaces. The with TS =100 °C, TA =300 °C, and 400 °C. At TA =300 °C, Sm–Co layer grows initially in an islanding mode with large the onset of the Fe layer reversal increases to over 4 kOe 10 roughness. When the Fe layer is deposited at a low TS, the from under 3 kOe for the TS =100 °C sample, while the Sm–Co/Fe interface is expected to be sharp but jagged. An- switching field of the hard layer becomes reduced. After an- nealing or depositing the Fe layer at elevated temperatures nealing at 400 °C, the hysteresis becomes single-phase like promotes interdiffusion between the Sm–Co and Fe, blurring with the coercivity greater than 6 kOe. The measured room- ͑ ͒ the interface and reducing the roughness. These microstruc- temperature saturation magnetization Ms for all samples of ϳ 3 ͑ ͒ tural characteristics are immediately evident in the cross- this composition is 930 emu/cm . The BH max value in- sectional EFTEM images shown in Fig. 1 for two creases from 24 MGOe for the TS =100 °C sample to ͑ ͒ ͑ ͒ Sm–Co 20 nm /Fe 20 nm samples with TS =100 °C, and 27.7 MGOe for the TA =300 °C sample, and then decreases Downloaded 30 Sep 2005 to 164.54.84.133.
Load more

Recommended publications
  • Effective Medium Theory of Magnetization Reversal in Magnetically Interacting Particles Heliang Qu and Jiangyu Li
    IEEE TRANSACTIONS ON MAGNETICS, VOL. 41, NO. 3, MARCH 2005 1093 Effective Medium Theory of Magnetization Reversal in Magnetically Interacting Particles Heliang Qu and JiangYu Li Abstract—We report an effective medium theory of magnetiza- One of the breakthroughs was made about ten years ago tion reversal and hysteresis in magnetically interacting particles, when an exchange coupling mechanism was proposed to en- where the intergranular magnetostatic interaction is accounted hance the energy product of permanent magnets [3]. The idea for by an effective medium approximation. We introduce two is to mix the magnetic hard and soft phases at nanoscale so dimensionless parameters, and H, that completely charac- terize the hysteresis in a ferromagnetic polycrystal when the that they can be coupled through the intergranular exchange grain size is much larger than the exchange length so that the interaction, leading to dramatically enhanced remanence and exchange coupling can be ignored. The competition between the energy product. This again highlights the importance of inter- anisotropy energy and the intergranular magnetostatic energy granular magnetic interactions, and calls for new models that is measured by , while the competition between the anisotropy can take those interactions into account. While micromagnetic energy and Zeeman’s energy is measured by H. The hysteresis loop, magnetostatic energy density, and anisotropy energy density simulations are able to explain the remanence enhancement in calculated by using this theory agrees well with micromagnetic exchange-spring magnets [4], they are often computationally simulations. The calculations also reveal that the subnucleation extensive and time-consuming. There are also earlier efforts to field switching due to the magnetic field fluctuation is important modify the Stoner–Wohlfarth model by Atherton and Beattie when the magnet is not very hard, and that has been accounted using a mean field correction [5], where a magnetic field pro- for by a probability-based switching model.
    [Show full text]
  • Practical Aspects of Modern and Future Permanent Magnets
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Ralph Skomski Publications Research Papers in Physics and Astronomy 2014 Practical Aspects of Modern and Future Permanent Magnets R.W. McCallum Ames Laboratory, Iowa State University, Ames, Iowa L. H. Lewis Northeastern University Ralph Skomski University of Nebraska-Lincoln, [email protected] M. J. Kramer US Department of Energy, Iowa State University I. E. Anderson US Department of Energy, Iowa State University Follow this and additional works at: https://digitalcommons.unl.edu/physicsskomski Part of the Engineering Physics Commons, and the Metallurgy Commons McCallum, R.W.; Lewis, L. H.; Skomski, Ralph; Kramer, M. J.; and Anderson, I. E., "Practical Aspects of Modern and Future Permanent Magnets" (2014). Ralph Skomski Publications. 98. https://digitalcommons.unl.edu/physicsskomski/98 This Article is brought to you for free and open access by the Research Papers in Physics and Astronomy at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Ralph Skomski Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. MR44CH17-McCallum ARI 9 June 2014 14:8 Practical Aspects of Modern and Future Permanent Magnets R.W. McCallum,1,2 L.H. Lewis,3 R. Skomski,4 M.J. Kramer,1,2 and I.E. Anderson1,2 1The Ames Laboratory, US Department of Energy, Iowa State University, Ames, Iowa 50011; email: [email protected], [email protected], [email protected] 2Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011 3Department of Chemical Engineering, Northeastern University, Boston, Massachusetts 02115; email: [email protected] 4Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588; email: [email protected] Annu.
    [Show full text]
  • Tailored Magnetic Properties of Exchange-Spring and Ultra Hard Nanomagnets
    Max-Planck-Institute für Intelligente Systeme Stuttgart Tailored Magnetic Properties of Exchange-Spring and Ultra Hard Nanomagnets Kwanghyo Son Dissertation An der Universität Stuttgart 2017 Tailored Magnetic Properties of Exchange-Spring and Ultra Hard Nanomagnets Von der Fakultät Mathematik und Physik der Universität Stuttgart zur Erlangung der Würde eines Doktors der Naturwissenschaften (Dr. rer. nat.) genehmigte Abhandlung Vorgelegt von Kwanghyo Son aus Seoul, SüdKorea Hauptberichter: Prof. Dr. Gisela Schütz Mitberichter: Prof. Dr. Sebastian Loth Tag der mündlichen Prüfung: 04. Oktober 2017 Max‐Planck‐Institut für Intelligente Systeme, Stuttgart 2017 II III Contents Contents ..................................................................................................................................... 1 Chapter 1 ................................................................................................................................... 1 General Introduction ......................................................................................................... 1 Structure of the thesis ....................................................................................................... 3 Chapter 2 ................................................................................................................................... 5 Basic of Magnetism .......................................................................................................... 5 2.1 The Origin of Magnetism .......................................................................................
    [Show full text]
  • Exchange Interactions and Curie Temperature of Ce-Substituted Smco5
    Article Exchange Interactions and Curie Temperature of Ce-Substituted SmCo5 Soyoung Jekal 1,2 1 Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland; [email protected] or [email protected] 2 Condensed Matter Theory Group, Paul Scherrer Institute (PSI), CH-5232 Villigen, Switzerland Received: 13 December 2018; Accepted: 8 January 2019; Published: 14 January 2019 Abstract: A partial substitution such as Ce in SmCo5 could be a brilliant way to improve the magnetic performance, because it will introduce strain in the structure and breaks the lattice symmetry in a way that enhances the contribution of the Co atoms to magnetocrystalline anisotropy. However, Ce substitutions, which are benefit to improve the magnetocrystalline anisotropy, are detrimental to enhance the Curie temperature (TC). With the requirements of wide operating temperature range of magnetic devices, it is important to quantitatively explore the relationship between the TC and ferromagnetic exchange energy. In this paper we show, based on mean-field approximation, artificial tensile strain in SmCo5 induced by substitution leads to enhanced effective ferromagnetic exchange energy and TC, even though Ce atom itself reduces TC. Keywords: mean-field theory; magnetism; exchange energy; curie temperature 1. Introduction Owing to the large magnetocrystalline anisotropy, high Curie temperature (TC) and saturation magnetization (Ms), Sm–Co compounds have drawn attention for the high-performance magnet [1–12]. The net performance of the magnet crucially depends on the inter-atomic interactions, which in turn depend on the local atomic arrangements. In order to improve the intrinsic magnetic properties of Sm–Co system, further approaches[5,7,9,12–19] have been attempted in the past few decades.
    [Show full text]
  • UNIVERSITY of CALIFORNIA, SAN DIEGO Development Of
    UNIVERSITY OF CALIFORNIA, SAN DIEGO Development of Thermoelectric and Permanent Magnet Nanoparticles for Clean Energy Applications A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Materials Science and Engineering by Phi-Khanh Nguyen Committee in Charge: Professor Ami Berkowitz, Co-Chair Professor Sungho Jin, Co-Chair Professor Prabhakar Bandaru Professor Renkun Chen Professor Eric Fullerton 2015 © Phi-Khanh Nguyen, 2015 All rights reserved. SIGNATURE PAGE The dissertation of Phi-Khanh Nguyen is approved, and it is acceptable in quality and form for publication on microfilm and electronically: Co-Chair Co-Chair University of California, San Diego 2015 iii DEDICATION Dedicated to my mother and father iv EPIGRAPH “Materials science is just common sense.” - Ami E. Berkowitz v TABLE OF CONTENTS SIGNATURE PAGE ......................................................................................................... iii DEDICATION ................................................................................................................... iv EPIGRAPH ......................................................................................................................... v TABLE OF CONTENTS ................................................................................................... vi LIST OF ABBREVIATIONS ............................................................................................ ix LIST OF FIGURES ...........................................................................................................
    [Show full text]
  • Exchange-Spring Behavior in Bimagnetic Cofe2o4/Cofe2
    Exchange-spring behavior in bimagnetic CoFe 2O4/CoFe 2 nanocomposite Leite, G. C. P.1, Chagas, E. F. 1, Pereira, R. 1, Prado, R. J. 1, Terezo, A. J. 2 , Alzamora, M. 3, and Baggio-Saitovitch, E. 3 1Instituto de Física , Universidade Federal de Mato Grosso, 78060-900, Cuiabá- MT, Brazil 2Departamento de Química, Universidade Federal do Mato Grosso, 78060-900, Cuiabá-MT, Brazil 3Centro Brasileiro de Pesquisas Físicas, Rua Xavier Sigaud 150 Urca. Rio de Janeiro, Brazil. Phone number: 55 65 3615 8747 Fax: 55 65 3615 8730 Email address: [email protected] Abstract In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe 2O4 and ferrimagnetic oxide/ferromagnetic metal CoFe 2O4/CoFe 2 nanocomposites. The latter compound is a good system to study hard ferrimagnet/soft ferromagnet exchange coupling. Two steps were used to synthesize the bimagnetic CoFe 2O4/CoFe 2 nanocomposites: (i) first preparation of CoFe 2O4 nanoparticles using the a simple hydrothermal method and (ii) second reduction reaction of cobalt ferrite nanoparticles using activated charcoal in inert atmosphere and high temperature. The phase structures, particle sizes, morphology, and magnetic properties of CoFe 2O4 nanoparticles have been investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) with applied field up to 3.0 kOe at room temperature and 50K. The mean diameter of CoFe 2O4 particles is about 16 nm. Mossbauer spectra reveal two sites for Fe3+. One site is related to Fe in an octahedral coordination and the other one to the Fe3+ in a tetrahedral coordination, as expected for a spinel crystal structure of CoFe 2O4.
    [Show full text]
  • Magnetic Anisotropy and Exchange in (001) Textured Fept-Based Nanostructures
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Theses, Dissertations, and Student Research: Department of Physics and Astronomy Physics and Astronomy, Department of 12-2013 Magnetic Anisotropy and Exchange in (001) Textured FePt-based Nanostructures Tom George University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/physicsdiss Part of the Condensed Matter Physics Commons George, Tom, "Magnetic Anisotropy and Exchange in (001) Textured FePt-based Nanostructures" (2013). Theses, Dissertations, and Student Research: Department of Physics and Astronomy. 31. https://digitalcommons.unl.edu/physicsdiss/31 This Article is brought to you for free and open access by the Physics and Astronomy, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Theses, Dissertations, and Student Research: Department of Physics and Astronomy by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. MAGNETIC ANISOTROPY AND EXCHANGE IN (001) TEXTURED FePt-BASED NANOSTRUCTURES by Tom Ainsley George A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy Major: Physics and Astronomy Under the Supervision of Professor David J. Sellmyer Lincoln, Nebraska December, 2013 MAGNETIC ANISOTROPY AND EXCHANGE IN (001) TEXTURED FePt-BASED NANOSTRUCTURES Tom Ainsley George, Ph.D. University of Nebraska, 2013 Adviser: David J. Sellmyer Hard-magnetic L10 phase FePt has been demonstrated as a promising candidate for future nanomagnetic applications, especially magnetic recording at areal densities approaching 10 Tb/in2. Realization of FePt’s potential in recording media requires control of grain size and intergranular exchange interactions in films with high degrees of L10 order and (001) crystalline texture, including high perpendicular magnetic anisotropy.
    [Show full text]
  • Strain Induced Anisotropic Magnetic Behaviour and Exchange Coupling Effect in Fe-Smco5 Permanent Magnets Generated by High Pressure Torsion
    STRAIN INDUCED ANISOTROPIC MAGNETIC BEHAVIOUR AND EXCHANGE COUPLING EFFECT IN FE-SMCO5 PERMANENT MAGNETS GENERATED BY HIGH PRESSURE TORSION APREPRINT Lukas Weissitsch Erich Schmid Institute of Materials Science, Austrian Academy of Sciences 8700 Leoben, Austria [email protected] Martin Stückler Erich Schmid Institute of Materials Science, Austrian Academy of Sciences 8700 Leoben, Austria Stefan Wurster Erich Schmid Institute of Materials Science, Austrian Academy of Sciences 8700 Leoben, Austria Peter Knoll Heinz Krenn Institute of Physics Institute of Physics University of Graz, 8010 Graz, Austria University of Graz, 8010 Graz, Austria Reinhard Pippan Erich Schmid Institute of Materials Science, Austrian Academy of Sciences 8700 Leoben, Austria Andrea Bachmaier Erich Schmid Institute of Materials Science, Austrian Academy of Sciences 8700 Leoben, Austria January 20, 2021 ABSTRACT High-pressure torsion (HPT), a technique of severe plastic deformation (SPD), is shown as a promising processing method for exchange-spring magnetic materials in bulk form. Powder mixtures of Fe and SmCo5 are consolidated and deformed by HPT exhibiting sample dimensions of several millimetres, arXiv:2101.03900v2 [cond-mat.mtrl-sci] 19 Jan 2021 being essential for bulky magnetic applications. The structural evolution during HPT deformation of Fe-SmCo5 compounds at room- and elevated- temperatures of chemical compositions consisting of 87, 47, 24 and 10 wt.% Fe is studied and microstructurally analysed. Electron microscopy and synchrotron X-ray diffraction reveal a dual-phase nanostructured composite for the as-deformed samples with grain refinement after HPT deformation. SQUID magnetometry measurements show hysteresis curves of an exchange coupled nanocomposite at room temperature, while for low temperatures a decoupling of Fe and SmCo5 is observed.
    [Show full text]
  • Understanding Magnetic Exchange Behavior in Core@Shell
    FLORIDA STATE UNIVERSITY COLLEGE OF ARTS AND SCIENCES UNDERSTANDING MAGNETIC EXCHANGE BEHAVIOR IN CORE@SHELL NANOPARTICLES By DAVID J CARNEVALE JR A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2017 David Carnevale defended this dissertation on November 20, 2017. The members of the supervisory committee were: Michael Shatruk Professor Co-Directing Dissertation Geoffrey F. Strouse Professor Co-Directing Dissertation Peng Xiong University Representative Joseph Schlenoff Committee Member The Graduate School has verified and approved the above-named committee members, and certifies that the dissertation has been approved in accordance with university requirements. ii Dedicated to Kate and Lily, this work is only possible thanks to your continued love and support. iii ACKNOWLEDGMENTS This work was done with the help of both the Shatruk and Strouse groups. Whether it be fielding my constant questions or simply just providing pleasant conversation, each and every person in both groups have contributed in some way. In particular, I want to thank Jeff Lengyel. Jeff has been a constant help with not only with his intellect, but also with his time in helping with different data collections and processing. Thanks to the joint wisdom of both Dr. Shatruk and Dr. Strouse, I have been able to work on a difficult project that I can take pride in. Through their understanding and insight of the project, we have been able to make significant strides in understanding magnetic exchange behavior. While it was not always easy for the three of us to agree on the science, the work was made all the better once we settled on the answers.
    [Show full text]
  • Analysis of Mechanically Milled Exchange Coupled Nanocomposite Permanent Magnets
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Mechanical (and Materials) Engineering -- Mechanical & Materials Engineering, Dissertations, Theses, and Student Research Department of Summer 2012 Analysis of Mechanically Milled Exchange Coupled Nanocomposite Permanent Magnets Santanu Mukherjee University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/mechengdiss Part of the Mechanical Engineering Commons Mukherjee, Santanu, "Analysis of Mechanically Milled Exchange Coupled Nanocomposite Permanent Magnets" (2012). Mechanical (and Materials) Engineering -- Dissertations, Theses, and Student Research. 41. https://digitalcommons.unl.edu/mechengdiss/41 This Article is brought to you for free and open access by the Mechanical & Materials Engineering, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Mechanical (and Materials) Engineering -- Dissertations, Theses, and Student Research by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Analysis of Mechanically Milled Exchange Coupled Nanocomposite Permanent Magnets by Santanu Mukherjee A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For The Degree of Master of Science Major: Mechanical Engineering Under the Supervision of Jeffrey E. Shield Lincoln, Nebraska May, 2011 Analysis of Mechanically Milled Exchange Coupled Nanocomposite Permanent Magnets Santanu Mukherjee University of Nebraska, 2012 Advisor: Jeffrey E. Shield Nanocomposite permanent magnets have recently evoked wide interest because of their interesting properties. They usually consist of a hard magnetic phase having superior coercivities and a soft magnetic phase having improved values of magnetization and when they are coupled together, we get a permanent magnet with enhanced values of both the parameters and thus can be put to a lot of applications.
    [Show full text]
  • Magnetic Phase Coexistence and Hard–Soft Exchange Coupling in Fept Nanocomposite Magnets
    nanomaterials Article Magnetic Phase Coexistence and Hard–Soft Exchange Coupling in FePt Nanocomposite Magnets O. Crisan 1,*, I. Dan 2, P. Palade 1, A. D. Crisan 1, A. Leca 1 and A. Pantelica 3 1 National Institute for Materials Physics, 077125 Magurele, Romania; palade@infim.ro (P.P.); alina.crisan@infim.ro (A.D.C.); aurel.leca@infim.ro (A.L.) 2 R&D Consulting and Services S.R.L., 023761 Bucharest, Romania; [email protected] 3 Horia Hulubei National Institute for Physics and Nuclear Engineering, P.O. Box MG-6, 077125 Magurele, Romania; apantel@ifin.nipne.ro * Correspondence: ocrisan@infim.ro Received: 2 July 2020; Accepted: 11 August 2020; Published: 18 August 2020 Abstract: With the aim of demonstrating phase coexistence of two magnetic phases in an intermediate annealing regime and obtaining highly coercive FePt nanocomposite magnets, two alloys of slightly off-equiatomic composition of a binary Fe-Pt system were prepared by dynamic rotation switching and ball milling. The alloys, with a composition Fe53Pt47 and Fe55Pt45, were subsequently annealed at 400 ◦C and 550 ◦C and structurally and magnetically characterized by means of X-ray diffraction, 57Fe Mössbauer spectrometry and Superconducting Quantum Interference Device (SQUID) magnetometry measurements. Gradual disorder–order phase transformation and temperature-dependent evolution of the phase structure were monitored using X-ray diffraction of synchrotron radiation. It was shown that for annealing temperatures as low as 400 ◦C, a predominant, highly ordered L10 phase is formed in both alloys, coexisting with a cubic L12 soft magnetic FePt phase. The coexistence of the two phases is evidenced through all the investigating techniques that we employed.
    [Show full text]
  • Lattice-Match Stabilization and Magnetic Properties of Metastable Epitaxial Permalloy-Disilicide Nanostructures on a Vicinal Si(111) Substrate
    nanomaterials Article Lattice-Match Stabilization and Magnetic Properties of Metastable Epitaxial Permalloy-Disilicide Nanostructures on a Vicinal Si(111) Substrate Anjan Bhukta 1, Dror Horvitz 2, Amit Kohn 1 and Ilan Goldfarb 1,* 1 Department of Materials Science and Engineering, The Iby and Aladar Fleischman Faculty of Engineering, Ramat Aviv, Tel Aviv University, Tel Aviv 6997801, Israel; [email protected] (A.B.); [email protected] (A.K.) 2 Thermo Fisher Scientific, Tel Aviv 7019900, Israel; dror.horvitz@thermofisher.com * Correspondence: [email protected] Abstract: We report the epitaxial formation of metastable γ-(FexNi1−x)Si2 nanostructure arrays resulting from the reaction of Ni80Fe20 permalloy with vicinal Si(111) surface atoms. We then explore the effect of structure and composition on the nanostructure’s magnetic properties. The low-temperature annealing (T < 600 ◦C) of a pre-deposited permalloy film led to solid-phase epitaxial nucleation of compact disk-shapedp islandp nanostructures decorating <110> ledges of the stepped surface, with either (2 × 2) or ( 3 × 3) R30◦ reconstructed flat top faces. High resolution scanning transmission electron microscopy analysis demonstrated fully coherent epitaxy of the islands with respect to the substrate, consistent with a well-matched CaF -prototype structure associated with 2 γ-FeSi2, along perfect atomically sharp interfaces. Energy dispersive spectroscopy detected ternary Citation: Bhukta, A.; Horvitz, D.; composition of the islands, with Fe and Ni atoms confined to the islands, and no trace of segregation. Kohn, A.; Goldfarb, I. Lattice-Match Our magnetometry measurements revealed the superparamagnetic behavior of the silicide islands, Stabilization and Magnetic Properties with a blocking temperature around 30 K, reflecting the size, shape, and dilute arrangement of the of Metastable Epitaxial islands in the assembly.
    [Show full text]