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Tai T.,University of Maryland University College | Xi X.X.,Temple University | Zhuang C.G.,Temple University | Mircea D.I.,Western Digital Media Inc. | Anlage S.M.,University of Maryland University College
IEEE Transactions on Applied Superconductivity

Niobium-based Superconducting Radio Frequency (SRF) cavity performance is sensitive to localized defects that give rise to quenches at high accelerating gradients. In order to identify these material defects on bulk Nb surfaces at their operating frequency and temperature, it is important to develop a new kind of wide bandwidth microwave microscopy with localized and strong RF magnetic fields. By taking advantage of write head technology widely used in the magnetic recording industry, one can obtain ̃200 mT RF magnetic fields, which is on the order of the thermodynamic critical field of Nb, on sub-micron length scales on the surface of the superconductor. We have successfully induced the nonlinear Meissner effect via this magnetic write head probe on a variety of superconductors. This design should have a high spatial resolution and is a promising candidate to find localized defects on bulk Nb surfaces and thin film coatings of interest for accelerator applications. © 2010 IEEE. Source

Sun C.-J.,Western Digital Media Inc. | Sun C.-J.,Argonne National Laboratory | Stafford D.,Western Digital Media Inc. | Acharya R.,Western Digital Media Inc.
IEEE Transactions on Magnetics

In order to demonstrate the strong and proper exchange coupling between bottom magnetic layer and capping magnetic layer in FePt-based exchange-coupled composite (ECC) perpendicular recording media, we have investigated the thermal stability, writability, degree of exchange coupling, and ECC gain factor of FePt-based ECC media as a function of the thickness of the capping FePt layer. With increasing the thickness of capping FePt layer, both thermal stability and media writability increase simultaneously as a result of the change from strong exchange coupling to proper exchange coupling. The proper exchange-coupled FePt ECC is a promising candidate for future high-density perpendicular recording. © 2006 IEEE. Source

Ma B.,University of Minnesota | Ma B.,Fudan University | Wang H.,University of Minnesota | Zhao H.,University of Minnesota | And 3 more authors.
IEEE Transactions on Magnetics

A core-shell type exchange-coupled composite (ECC) structure is developed with an L10 phase FePt core and an Fe shell. Coercivity decreases from 30.6 kOe for the FePt granular film with a very thin thickness of 3.2 nm, to 7.85 kOe for the FePt/Fe core-shell type granular film with a 3-nm-thick Fe. The energy barriers of the FePt/Fe films are measured by using Sharrock equation. A modified formula of gain factor considering the effect of films' thickness is proposed. Core-shell type FePt/Fe ECC granular film has a large advantage over a conventional granular film for media application. © 2006 IEEE. Source

Ma B.,University of Minnesota | Ma B.,Fudan University | Wang H.,University of Minnesota | Zhao H.,University of Minnesota | And 3 more authors.
Journal of Applied Physics

Structural and magnetic properties of core-shell type L10 FePt/Fe exchange coupled nanocomposites are studied systematically. Core-shell nanocomposites with FePt core and Fe shell are obtained by depositing Fe cap layers on granular L10 FePt films. Epitaxial growth is disclosed by x-ray diffraction. Coercivity decreases drastically for FePt/Fe with the thickness increase of Fe cap layers. The coercivity reduction is due to the much increased domain wall area pinned and compressed at the soft-hard interface, and the tilted effective easy axis because of the presence of demagnetized energy. L10 FePt/Fe with a 3 nm Fe layer has high thermal stability and gain factor for media applications. © 2011 American Institute of Physics. Source

Valcu B.,Western Digital Media Inc. | Seki T.,Western Digital Media Inc. | Chernyshov A.,Western Digital Media Inc. | Zong F.,Western Digital Media Inc. | Ajan A.,Western Digital Media Inc.
IEEE Transactions on Magnetics

Recording experiments were performed on FePt media with varying thermal layers thickness values. As the heat sink increases we observe that jitter decreases, due to improved thermal gradient. At the same time the laser power required to write on media increases. A semianalytical integrated optical and thermal model sheds light onto these experimental findings. © 1965-2012 IEEE. Source

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