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Dive into the research topics where Guohan Hu is active.

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Featured researches published by Guohan Hu.


Journal of Applied Physics | 2005

Magnetic dot arrays with multiple storage layers

M. Albrecht; Guohan Hu; A. Moser; O. Hellwig; Bruce D. Terris

An approach to increasing the data storage density of magnetic recording was investigated wherein dot arrays are combined with multiple magnetic storage layers. The latter consists of two magnetically decoupled perpendicular Co∕Pd multilayer stacks. As a result of the difference in the coercivity between the two stacks, the orientation of the remanent magnetization of each stack can be set independent of the orientation of the other layer. Therefore, each dot allows storing four different magnetization states, which give rise to four different readback signal levels. Thus, the investigated media structure allows doubling the storage density in magnetic recording applications. It was found that even for thick spacer layers a weak magnetostatic coupling of the storage layers is present preferring ferromagnetic alignment of the storage layers.


Journal of Applied Physics | 2004

Magnetic and recording properties of Co/Pd islands on prepatterned substrates

Guohan Hu; T. Thomson; M. Albrecht; M. E. Best; Bruce D. Terris; C. T. Rettner; Simone Raoux; Gary M. McClelland; Mark W. Hart

Magnetically isolated single domain islands with perpendicular anisotropy have been prepared by depositing Co/Pd multilayer films on prepatterned sub-50 nm SiO2/Si islands. The island arrays were fabricated by both direct write electron beam lithography and nanoimprinting. Nanoimprinting allows the creation of large area, 4 mm×4 mm, samples appropriate for characterization by conventional measurement techniques. Magnetic force microscopy and vibrating sample magnetometry showed that the reversal behavior of the patterned islands is quite different from that of the continuous films with a large increase in both switching field and switching field distribution. Recording on island arrays with a periodicity of 100 nm, produced from prepatterned substrates, was demonstrated using a quasistatic tester.


Journal of Applied Physics | 2005

Magnetization reversal in Co∕Pd nanostructures and films

Guohan Hu; T. Thomson; C. T. Rettner; Simone Raoux; Bruce D. Terris

The magnetic field required to reverse a Co∕Pd multilayer film with perpendicular anisotropy is greatly increased when the film is deposited onto patterned islands. The variation of the reversal field with Co thickness demonstrates that the island switching field is determined principally by the anisotropy. For sufficiently small islands the reversal field is close to that calculated using the Stoner–Wohlfarth (SW) model and these small islands show the expected SW angle dependence. A similar SW angle dependence is also observed for the larger islands. We propose that for the larger islands reversal is governed by a nucleation event, which has SW characteristics, followed by rapid domain wall motion.The magnetic field required to reverse a Co∕Pd multilayer film with perpendicular anisotropy is greatly increased when the film is deposited onto patterned islands. The variation of the reversal field with Co thickness demonstrates that the island switching field is determined principally by the anisotropy. For sufficiently small islands the reversal field is close to that calculated using the Stoner–Wohlfarth (SW) model and these small islands show the expected SW angle dependence. A similar SW angle dependence is also observed for the larger islands. We propose that for the larger islands reversal is governed by a nucleation event, which has SW characteristics, followed by rapid domain wall motion.


IEEE Transactions on Magnetics | 2005

Recording and reversal properties of nanofabricated magnetic islands

Bruce D. Terris; M. Albrecht; Guohan Hu; T. Thomson; C. T. Rettner

Patterned media are a promising approach for future high density magnetic recording. In order to reliably address individual bits, a recording head will be required to reverse a selected island without disturbing neighboring islands. This leads to a requirement for islands with a narrow switching field distribution. We review the switching and recording properties of patterned granular CoPtCr-based films, and present results on the reversal properties of topographically patterned Co/Pd multilayer films, with particular emphasis on switching field distributions. Finally, the use of islands with multiple storage layers is demonstrated as a potential route to even higher storage density without the need for smaller, lithographically defined islands.


IEEE Transactions on Magnetics | 2005

Rotation and wall propagation in multidomain Co/Pd islands

Guohan Hu; T. Thomson; C. T. Rettner; B. D. Terris

Patterned magnetic structures with sizes ranging from 30 nm to 5 /spl mu/m have been fabricated to investigate the magnetization reversal of Co/Pd islands with perpendicular anisotropy. The nucleation field for reversal in islands capable of supporting a multidomain ground state (size ranging from 200 nm to 5 /spl mu/m) is higher than the domain wall propagation field and is characterized by a Stoner-Wohlfarth-like angle dependence. Pre-reversed nucleation sites in the islands leads to the 1/cos(/spl theta/) switching behavior indicative of domain wall motion.


Journal of Applied Physics | 2005

Angular dependence of the switching field in patterned magnetic elements

Rok Dittrich; Guohan Hu; T. Schrefl; T. Thomson; Dieter Suess; Bruce D. Terris; J. Fidler

Recent experimental studies on the switching behaviour of Co∕Pd multilayer islands with sizes in a range from 20–100 nm shows the classical angular dependence for uniform rotation. We compare measured angular dependence of the switching field with micromagnetic finite element simulations. Simulation results show reversal modes close to uniform rotation for islands smaller than 30 nm. Larger islands (>70nm) reverse by nucleation of a reversed domain followed by domain wall propagation. However, the angular dependence does not change its character with the island size. The nucleation of the reversed domain determines the switching field.


ieee international magnetics conference | 2005

Magnetic and recording properties of patterned perpendicular islands

Bruce D. Terris; Guohan Hu; M. Albrecht; T. Thomson; C. T. Rettner

Patterned media are one of the approaches to achieving 500 Gb/in/sup 2/ and beyond recording densities. This paper presents an overview of a number of aspects of discrete bit media, including fabrication techniques, recording properties, and fundamental magnetic switching studies. The use of focused ion beam patterning is described as a means to fabricate 50 nm CoPtCr single domain islands. Recording results on such arrays using a quasi-static tester is presented and head synchronization requirements, jitter and SNR data is discussed. The importance of island switching field distribution as well as write head field gradient is shown. However, while FIB is a very convenient means of fabricating test structures, it is slow and not amenable to mass production of patterned disks.


ieee international magnetics conference | 2005

Nanofabrication as a probe of anisotropy distribution in Co/Pd multilayers

Guohan Hu; T. Thomson; Bruce D. Terris

In an attempt to determine, in one system, if the source of the broad island switching field distribution (SFD) arises from intrinsic film properties or from extrinsic sources, such as lithography variations, arrays of patterned Co/Pd magnetic islands with perpendicular anisotropy are fabricated. The islands display single domain remanent states after easy axis saturation, as observed by magnetic Kerr effect and magnetic force measurements. Both the coercivity and width of the SFD of the island array increase with decreasing island size.


Physical Review Letters | 2006

Intrinsic Distribution of Magnetic Anisotropy in Thin Films Probed by Patterned Nanostructures

T. Thomson; Guohan Hu; Bruce D. Terris


Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems | 2006

Patterned media for future magnetic data storage

Bruce D. Terris; T. Thomson; Guohan Hu

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M. Albrecht

University of Augsburg

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Dieter Suess

Vienna University of Technology

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T. Schrefl

Danube University Krems

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Denys Makarov

Helmholtz-Zentrum Dresden-Rossendorf

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F. Treubel

University of Konstanz

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