Neutrons to Probe Nanoscale Magnetism in Perpendicular Magnetic Recording Media PDF Download

Author: Vikash Venkataramana
Publisher:
ISBN:
Category : Data disk drives
Languages : en
Pages : 0

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Author: Vikash Venkataramana
Publisher:
ISBN:
Category : Data disk drives
Languages : en
Pages : 410

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Magnetic recording media refers to the disc shaped thin film magnetic medium present inside the hard disk drive of a computer. Magnetic recording is an important function of the hard disk drive by which information such as text, pictures, audio and videos are stored. Information is broken down to a simple binary format and is stored as magnetised bits along the tracks of the disk forming the hard drive. Over the years advancements in research on the type of magnetic materials used has allowed increased data storage capacities by reducing magnetic bit sizes. It is with this advancement in magnetic data storage, that we have today's hard disk drive technology, which uses a perpendicular magnetic medium to store data. A perpendicular magnetic medium is a multi-layered magnetic thin film structure with the topmost layer comprising nanoscale magnetic grains of high perpendicular anisotropy. The topmost recording layer (RL) is mapped into individual bits of 80-100 nm2 area that consist of 5-10 nm diameter CoCrPt grains, embedded in an oxide matrix. A bit area is defined to ensure a significant number of stable grains allowing data to be stored in each bit as a '0' or a '1' depending on its switched magnetic state. The magnetic grains if sputtered below a threshold grain size tend to suffer from thermal fluctuation and instability due to super-paramagnetic effects, hence bringing limitations to grain size. As a result of this, research in recent years has been directed at introducing a softer magnetic exchange coupled composite (ECC) layer above the recording layer. This layer facilitates the delicate balance of switching smaller grains with strong magneto-crystalline anisotropy at lower magnetic fields, by exchange coupling with the CoCrPt grains in the recording layer. However this technique of increasing the efficiency in the perpendicular magnetic medium by introducing 'facilitating' layers is an area that is still being widely researched and understood. Although numerous surface and bulk analysis techniques exist to study magnetic and surface properties of these materials, there is limited information on the structural and magnetic properties of these materials at the nanoscale level. The reported work investigates the structural and magnetic properties of the magnetic grains and multi-layers in the perpendicular magnetic medium using polarised neutron scattering and reflectivity techniques. The work investigates the structural and magnetic properties of the CoCrPt grains, apart from understanding the CoCrPt magnetic grain switching. The work also investigates the magnetisation in the layers of the thin film perpendicular media structure using polarised neutron reflectivity (PNR). Using polarised small angle neutron scattering (PolSANS), it has been shown that ferromagnetic ordered core region of the CoCrPt grain in the recording layer is smaller than the physical CoCrPt granular structure. The magnetic switching behaviour of the CoCrPt grain at different magnetic fields is also analysed and the experimental PolSANS data is fitted with non-interacting size-dependent analytical grain switching models. This result provides significant evidence that the magnetic anisotropy increases with grain size, with larger magnetic grains having larger magnetic anisotropy. Polarised neutron scattering experiments are carried out with the magnetically softer exchange coupled composite (ECC) layer included in the thin film magnetic structure. The first experiments investigate if the ECC layer contributes to the nuclear and magnetic interference scattering term in the experimenting scattering data. The experiments clearly show that there is no contribution from the ECC layer in the nuclear and magnetic scattering interference term. The role of the ECC layer in the magnetic switching process is then investigated at different magnetic fields. The ECC layer was found to influence the size-dependent magnetic grain switching of the CoCrPt grains in the recording layer and a detailed investigation is presented in the reported work. Polarised neutron reflectivity (PNR) experiments have also been carried out with the ECC layer on the perpendicular magnetic media samples. These experiments investigate the composition and thickness of the thin film structure, while also providing information on the magnetic state of the thin films under the influence of an in-plane magnetic field. The in-plane magnetisation in the recording and ECC layer is determined at different in-plane magnetic fields. The magnetisation values determined for the ECC layer and the recording layer (RL) at different in-plane magnetic fields help better understand the differences in their magnetic properties.

Author: Andreas Michels
Publisher: Oxford University Press
ISBN: 0198855176
Category : Science
Languages : en
Pages : 374

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Magnetic Small-Angle Neutron Scattering provides the first extensive treatment of magnetic small-angle neutron scattering (SANS). The theoretical background required to compute magnetic SANS cross sections and correlation functions related to long-wavelength magnetization structures is laidout. The concepts are scrutinized based on the discussion of experimental neutron data. Regarding prior background knowledge, some familiarity with the basic magnetic interactions and phenomena as well as scattering theory is desired.Besides exposing the different origins of magnetic SANS, and furnishing the basics of the magnetic SANS technique in early chapters, a large part of the book is devoted to a comprehensive treatment of the continuum theory of micromagnetics, as it is relevant for the study of the elastic magneticSANS cross section. Analytical expressions for the magnetization Fourier components allow to highlight the essential features of magnetic SANS and to analyze experimental data both in reciprocal, as well as in real space. Later chapters provide an overview on the magnetic SANS of nanoparticles andso-called complex systems (e.g., ferrofluids, magnetic steels, spin glasses and amorphous magnets). It is this subfield where major progress is expected to be made in the coming years, mainly via the increased usage of numerical micromagnetic simulations (Chapter 7), which is a very promisingapproach for the understanding of the magnetic SANS from systems exhibiting nanoscale spin inhomogeneity.

Author:
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 2626

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Author: Hari Singh Nalwa
Publisher:
ISBN: 9781588830005
Category : Science
Languages : en
Pages : 0

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Twelve contributions comprise a reference source that is a coherent presentation of the state of the art in this fast growing area of nanotechnology research. Magnetic nanostructures are important for their phenomenal potential for storage; their great commercial value will come from applications in

Author: Teruya Shinjo
Publisher: Elsevier
ISBN: 0444632778
Category : Science
Languages : en
Pages : 373

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The concise and accessible chapters of Nanomagnetism and Spintronics, Second Edition, cover the most recent research in areas of spin-current generation, spin-calorimetric effect, voltage effects on magnetic properties, spin-injection phenomena, giant magnetoresistance (GMR), and tunnel magnetoresistance (TMR). Spintronics is a cutting-edge area in the field of magnetism that studies the interplay of magnetism and transport phenomena, demonstrating how electrons not only have charge but also spin. This second edition provides the background to understand this novel physical phenomenon and focuses on the most recent developments and research relating to spintronics. This exciting new edition is an essential resource for graduate students, researchers, and professionals in industry who want to understand the concepts of spintronics, and keep up with recent research, all in one volume. Provides a concise, thorough evaluation of current research Surveys the important findings up to 2012 Examines the future of devices and the importance of spin current

Author: Nicholas J. Darton
Publisher: Cambridge University Press
ISBN: 1107031095
Category : Medical
Languages : en
Pages : 317

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Drawing together topics from a wide range of disciplines, and featuring up-to-date examples of clinical usage and research applications, this text provides a comprehensive insight into the fundamentals of magnetic biosensors and the applications of magnetic nanoparticles in medicine.

Author: Michael Coey
Publisher: Springer
ISBN: 9783030632083
Category : Science
Languages : en
Pages : 1679

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This handbook presents a comprehensive survey of magnetism and magnetic materials. The dramatic advances in information technology and electromagnetic engineering make it necessary to systematically review the approved key knowledge and summarize the state of the art in this vast field within one seminal reference work. The book thus delivers up-to-date and well-structured information on a wealth of topics encompassing all fundamental aspects of the underlying physics and materials science, as well as advanced experimental methodology and applications. It features coverage of the host of fascinating and complex phenomena that arise from the use of magnetic fields in e.g. chemistry and biology. Edited by two internationally renowned scholars and featuring authored chapters from leading experts in the field, Springer’s Handbook of Magnetism and Magnetic Materials is an invaluable source of essential reference information for a broad audience of students, researchers, and magnetism professionals.

Author: J. M. D. Coey
Publisher: Cambridge University Press
ISBN: 0521816149
Category : Science
Languages : en
Pages : 632

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An essential textbook for graduate courses on magnetism and an important source of practical reference data.

Author: Masud Mansuripur
Publisher: Cambridge University Press
ISBN: 9780521634182
Category : Science
Languages : en
Pages : 780

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First-time paperback of successful and well-reviewed book; for graduate students and researchers in physics and engineering.