Theoretical Investigation of New Magnetic Recording Media Using an Energy Landscape Method PDF Download
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Author: Ru Zhu
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 83
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Book Description
Magnetic material has played an important role in the information storage technology. We have worked out a phase diagram showing spin torque switching for perpendicular anisotropy media at nonzero temperature. A new area is predicted where the system can vibrate between precessional and parallel states quickly and therefore creates "telegraph" noise region. The result was later confirmed by a nanopillar experiment. The density of magnetic recording is restricted by the superparamagnetic limit. To overcome this limit people have used perpendicular recording to replace the traditional longitudinal recording and are working on other approaches to get over the superparamagnetic limit including heat assisted recording, patterned media and exchange coupled media. Anisotropy graded media provides an alternative solution to achieve high areal density while keeping the writing field relatively low and good thermal stability. A two-dimensional energy landscape of the switching of anisotropy graded media is calculated to give an intuitive way of understanding the switching, as well as a way to quantitatively calculate the switching rate by mapping the problem onto a one-dimensional Langevin random walk. Then an iterative algorithm of for finding the saddle point of the energy landscape, which we call barbell algorithm, is used to locate the saddle point and the whole switching trajectory.
Author: Ru Zhu
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 83
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Book Description
Magnetic material has played an important role in the information storage technology. We have worked out a phase diagram showing spin torque switching for perpendicular anisotropy media at nonzero temperature. A new area is predicted where the system can vibrate between precessional and parallel states quickly and therefore creates "telegraph" noise region. The result was later confirmed by a nanopillar experiment. The density of magnetic recording is restricted by the superparamagnetic limit. To overcome this limit people have used perpendicular recording to replace the traditional longitudinal recording and are working on other approaches to get over the superparamagnetic limit including heat assisted recording, patterned media and exchange coupled media. Anisotropy graded media provides an alternative solution to achieve high areal density while keeping the writing field relatively low and good thermal stability. A two-dimensional energy landscape of the switching of anisotropy graded media is calculated to give an intuitive way of understanding the switching, as well as a way to quantitatively calculate the switching rate by mapping the problem onto a one-dimensional Langevin random walk. Then an iterative algorithm of for finding the saddle point of the energy landscape, which we call barbell algorithm, is used to locate the saddle point and the whole switching trajectory.
Author: Tim Rausch
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Author: M.L. Plumer
Publisher: Springer
ISBN: 9783642626869
Category : Science
Languages : en
Pages : 0
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Book Description
Application-oriented book on magnetic recording, focussing on the underlying physical mechanisms that play crucial roles in medium and transducer development for high areal density disk drives.
Author: Zhihong Lu
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 184
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Book Description
Anisotropy graded media is promising to overcome the writability problem in achieving ultrahigh areal density for magnetic recording media. To more conveniently study and compare various media with regard to a particular figure of merit, a new energy landscape method of analysis is suggested. Using this method, the theoretical limit of the figure of merit for a graded medium is found to be 4. This limit can be approached by a graded medium with anisotropy quadratically increasing from zero to its maximum value. In order to characterize the anisotropy distribution of a graded medium, hard axis loops of graded media with various anisotropy profiles are simulated and analyzed. It is found that the second derivative of the hard axis loop can give useful information on the anisotropy distribution in a graded medium. Fe50Pt50 with the L10 structure, as one of the magnetically hardest materials, has great potential for media application. By using a first-principles calculation method, the magnetic and electronic structures of L10 structured Fe50Pt50 have been studied. These calculations show that although the ferromagnetic phase is the most stable phase for Fe50Pt50 with the L10 structure, there is a competition between the antiferromagnetic and the ferromagnetic phases when the ratio of lattice constants, c/a, decreases. Experimental investigations of Fe50Pt50 films with graded order parameter fabricated by varying the growth temperature during deposition demonstrate that these films have much smaller switching field than fully ordered Fe50Pt50, which suggests it is possible to make graded media by using this kind of films. Fe100-xPtx films with compositional gradient were also studied; however, the large easy axis dispersion in these films makes them unsuitable for the fabrication of graded media. Films with [FePt3ordered)/FePt3 (disordered)]n superlattices were deposited on MgO substrates and sapphire substrates. It was found that the exchange bias in superlattices deposited on MgO substrate show higher exchange bias field. Polarized neutron reflectivity results show that ferromagnetic layers on MgO substrates contain more antiferromagnetic component than those on sapphire substrates. The larger exchange bias of the superlattice on MgO substrate is hypothesized to be due to larger exchange bias in its ferromagnetic layers.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 88
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Book Description
The Bulletin of the Atomic Scientists is the premier public resource on scientific and technological developments that impact global security. Founded by Manhattan Project Scientists, the Bulletin's iconic "Doomsday Clock" stimulates solutions for a safer world.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 994
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Author: Bruce J Berne
Publisher: World Scientific
ISBN: 9814496057
Category : Science
Languages : en
Pages : 881
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Book Description
The school held at Villa Marigola, Lerici, Italy, in July 1997 was very much an educational experiment aimed not just at teaching a new generation of students the latest developments in computer simulation methods and theory, but also at bringing together researchers from the condensed matter computer simulation community, the biophysical chemistry community and the quantum dynamics community to confront the shared problem: the development of methods to treat the dynamics of quantum condensed phase systems.This volume collects the lectures delivered there. Due to the focus of the school, the contributions divide along natural lines into two broad groups: (1) the most sophisticated forms of the art of computer simulation, including biased phase space sampling schemes, methods which address the multiplicity of time scales in condensed phase problems, and static equilibrium methods for treating quantum systems; (2) the contributions on quantum dynamics, including methods for mixing quantum and classical dynamics in condensed phase simulations and methods capable of treating all degrees of freedom quantum-mechanically.
Author:
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ISBN:
Category : Electrical engineering
Languages : en
Pages : 2240
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 116
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Book Description
The Bulletin of the Atomic Scientists is the premier public resource on scientific and technological developments that impact global security. Founded by Manhattan Project Scientists, the Bulletin's iconic "Doomsday Clock" stimulates solutions for a safer world.
Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 684
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