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Modifying the magnetic properties of Laves phase intermetallic multilayers and films by nano-patterning and ion implantation

Modifying the magnetic properties of Laves phase intermetallic multilayers and films by nano-patterning and ion implantation
Modifying the magnetic properties of Laves phase intermetallic multilayers and films by nano-patterning and ion implantation
Since the pioneering work of Kneller & Hawig and Skomski & Coey some 20 years
ago, the topic of exchange springs has received considerable attention. Exchange
springs, systems where thin hard and soft magnetic layers are alternately arranged in
multilayer stacks, provide great potential in improving the performance of a wide range
of devices, from permanent hard magnets and microelectromechanical sensors and
actuators, to magnetoresistive random access memory and permanent magnetic data
storage. Artificial structuring on the nano-scale will be beneficial in improving the
functionality of exchange spring systems in all of these areas. In this work, two
distinctly different routes to nano-structuring in epitaxially grown rare earth – iron
(REFe2) films and exchange spring materials are described. Namely i) electron beam
lithography and Ar+ ion milling to define three-dimensional nano-scale structures, and
ii) ion implantation to directly alter the crystalline structure of the material at the
atomic-scale. Nano-scale elements defined in REFe2 exchange spring materials are
presented, providing not only the first demonstration of nano-structuring in these
materials, but also the successful implementation of electron beam lithography and Ar+
ion milling on these novel systems. Nano-scale patterning confirms the suitability of
the REFe2 exchange spring materials as excellent candidates for magnetic data storage
media, since they remain relatively unaffected by nano-structuring, retaining their
thermal stability and comparatively small coercivity. Ar+ ion implantation is shown to
be effective at artificial structuring on the atomic-scale. In addition, energetic Ar+ ions
have been successfully used to accurately control the easy and hard axes of
magnetization within epitaxial YFe2 and DyFe2 films and a DyFe2 / YFe2 exchange
spring multilayer. At a fluence of ~ 1017 Ar+ ions cm-2, the magnetoelastic anisotropy
(dominant at room temperature in the epitaxially grown films) is reduced to such an
extent that the intrinsic magnetocrystalline anisotropy begins to dominate. Thus Ar+ ion
implantation serves to alter the easy and hard axes of magnetization, rotating them
through 90°. Such behaviour is clearly evident in hysteresis loops obtained by both the
magneto optical Kerr effect and vibrating sample magnetometry, and is further
confirmed by micromagnetic modelling. The reduction in magnetoelastic anisotropy is
attributed to energetic Ar+ ions causing RE atoms to relax to their unstrained lattice
positions, thereby relieving the strain responsible for the magnetoelastic anisotropy.
This interpretation is confirmed by X-ray diffraction measurements.
Buckingham, Andrew Roger
368d24d7-77da-4465-9205-55c4beda6e6e
Buckingham, Andrew Roger
368d24d7-77da-4465-9205-55c4beda6e6e
de Groot, Peter
98c21141-cf90-4e5c-8f2b-d2aae8efb84d

Buckingham, Andrew Roger (2010) Modifying the magnetic properties of Laves phase intermetallic multilayers and films by nano-patterning and ion implantation. University of Southampton, School of Physics and Astronomy, Doctoral Thesis, 290pp.

Record type: Thesis (Doctoral)

Abstract

Since the pioneering work of Kneller & Hawig and Skomski & Coey some 20 years
ago, the topic of exchange springs has received considerable attention. Exchange
springs, systems where thin hard and soft magnetic layers are alternately arranged in
multilayer stacks, provide great potential in improving the performance of a wide range
of devices, from permanent hard magnets and microelectromechanical sensors and
actuators, to magnetoresistive random access memory and permanent magnetic data
storage. Artificial structuring on the nano-scale will be beneficial in improving the
functionality of exchange spring systems in all of these areas. In this work, two
distinctly different routes to nano-structuring in epitaxially grown rare earth – iron
(REFe2) films and exchange spring materials are described. Namely i) electron beam
lithography and Ar+ ion milling to define three-dimensional nano-scale structures, and
ii) ion implantation to directly alter the crystalline structure of the material at the
atomic-scale. Nano-scale elements defined in REFe2 exchange spring materials are
presented, providing not only the first demonstration of nano-structuring in these
materials, but also the successful implementation of electron beam lithography and Ar+
ion milling on these novel systems. Nano-scale patterning confirms the suitability of
the REFe2 exchange spring materials as excellent candidates for magnetic data storage
media, since they remain relatively unaffected by nano-structuring, retaining their
thermal stability and comparatively small coercivity. Ar+ ion implantation is shown to
be effective at artificial structuring on the atomic-scale. In addition, energetic Ar+ ions
have been successfully used to accurately control the easy and hard axes of
magnetization within epitaxial YFe2 and DyFe2 films and a DyFe2 / YFe2 exchange
spring multilayer. At a fluence of ~ 1017 Ar+ ions cm-2, the magnetoelastic anisotropy
(dominant at room temperature in the epitaxially grown films) is reduced to such an
extent that the intrinsic magnetocrystalline anisotropy begins to dominate. Thus Ar+ ion
implantation serves to alter the easy and hard axes of magnetization, rotating them
through 90°. Such behaviour is clearly evident in hysteresis loops obtained by both the
magneto optical Kerr effect and vibrating sample magnetometry, and is further
confirmed by micromagnetic modelling. The reduction in magnetoelastic anisotropy is
attributed to energetic Ar+ ions causing RE atoms to relax to their unstrained lattice
positions, thereby relieving the strain responsible for the magnetoelastic anisotropy.
This interpretation is confirmed by X-ray diffraction measurements.

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Published date: March 2010
Organisations: University of Southampton

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Local EPrints ID: 161177
URI: http://eprints.soton.ac.uk/id/eprint/161177
PURE UUID: 23b5ce4a-77bf-48ca-9932-2600a21cf0d2

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Date deposited: 06 Aug 2010 15:46
Last modified: 29 Jan 2020 14:09

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