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Micromagnetic simulation of ferromagnetic part-spherical particles

Micromagnetic simulation of ferromagnetic part-spherical particles
Micromagnetic simulation of ferromagnetic part-spherical particles
The paramagnetic size limit for current magnetic storage media, particularly in sputtered grain storage, is being approached rapidly. To further increase media storage density, patterned media can be used which only need a single grain to store one bit of data. Chemical self-assembly techniques offer cost-effective methods to create templates, from which periodic arrays of magnetic structures can be formed. In contrast to systems of dots prepared by standard lithography, which have a cylindrical shape, dots prepared by chemical self-assembly template techniques are often spherical or part spherical in shape. In this article, we investigate the properties of such magnetic shapes using micromagnetic simulations. To represent accurately the geometry produced through chemical self-assembly methods, we attach a partial sphere (lower part) to a small ellipsoidal dome. We compute the hysteresis loops for various dot sizes and compare them with experimental results. In those below a critical diameter (140 nm in nickel), the hysteresis loop is square-like, resembling the uniform rotation of magnetization once the critical field is exceeded. For larger sizes, the hysteresis loop reverses reversibly around zero applied field but shows minor loops, placed symmetrically at the onset of magnetization reversal. These correspond to vortices penetrating and exiting the structure. In summary, we find that the coercive field of the droplets becomes zero above a critical diameter where the magnetization reversal behavior changes from single domain-like to vortex-like. Our results agree with experimental measurements performed on such structures.
0021-8979
7037-7039
Boardman, Richard P.
5818d677-5732-4e8a-a342-7164dbb10df1
Fangohr, Hans
9b7cfab9-d5dc-45dc-947c-2eba5c81a160
Cox, Simon J.
0e62aaed-24ad-4a74-b996-f606e40e5c55
Goncharov, Alexander V.
5ea6d47d-6a84-4aea-b749-5d49af361b17
Zhukov, Alexander A.
75d64070-ea67-4984-ae75-4d5798cd3c61
de Groot, P.A.J.
98c21141-cf90-4e5c-8f2b-d2aae8efb84d
Boardman, Richard P.
5818d677-5732-4e8a-a342-7164dbb10df1
Fangohr, Hans
9b7cfab9-d5dc-45dc-947c-2eba5c81a160
Cox, Simon J.
0e62aaed-24ad-4a74-b996-f606e40e5c55
Goncharov, Alexander V.
5ea6d47d-6a84-4aea-b749-5d49af361b17
Zhukov, Alexander A.
75d64070-ea67-4984-ae75-4d5798cd3c61
de Groot, P.A.J.
98c21141-cf90-4e5c-8f2b-d2aae8efb84d

Boardman, Richard P., Fangohr, Hans, Cox, Simon J., Goncharov, Alexander V., Zhukov, Alexander A. and de Groot, P.A.J. (2004) Micromagnetic simulation of ferromagnetic part-spherical particles. Journal of Applied Physics, 95 (11), 7037-7039. (doi:10.1063/1.1688639).

Record type: Article

Abstract

The paramagnetic size limit for current magnetic storage media, particularly in sputtered grain storage, is being approached rapidly. To further increase media storage density, patterned media can be used which only need a single grain to store one bit of data. Chemical self-assembly techniques offer cost-effective methods to create templates, from which periodic arrays of magnetic structures can be formed. In contrast to systems of dots prepared by standard lithography, which have a cylindrical shape, dots prepared by chemical self-assembly template techniques are often spherical or part spherical in shape. In this article, we investigate the properties of such magnetic shapes using micromagnetic simulations. To represent accurately the geometry produced through chemical self-assembly methods, we attach a partial sphere (lower part) to a small ellipsoidal dome. We compute the hysteresis loops for various dot sizes and compare them with experimental results. In those below a critical diameter (140 nm in nickel), the hysteresis loop is square-like, resembling the uniform rotation of magnetization once the critical field is exceeded. For larger sizes, the hysteresis loop reverses reversibly around zero applied field but shows minor loops, placed symmetrically at the onset of magnetization reversal. These correspond to vortices penetrating and exiting the structure. In summary, we find that the coercive field of the droplets becomes zero above a critical diameter where the magnetization reversal behavior changes from single domain-like to vortex-like. Our results agree with experimental measurements performed on such structures.

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Published date: 2004

Identifiers

Local EPrints ID: 22791
URI: https://eprints.soton.ac.uk/id/eprint/22791
ISSN: 0021-8979
PURE UUID: cf9c4197-8b21-439a-91a2-2352f9e3a09d

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Date deposited: 22 Mar 2006
Last modified: 18 Jul 2019 12:39

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