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Pal S.,Thematic Unit of Excellence on Nanodevice Technology | Klos J.W.,ckiewicz University In Poznan | Das K.,Thematic Unit of Excellence on Nanodevice Technology | Hellwig O.,A Western Digital Company | And 3 more authors.
Applied Physics Letters | Year: 2014

We present an all-optical time-resolved measurement of spin wave (SW) dynamics in a series of antidot lattices based on [Co(0.75nm)/Pd(0.9nm)]8 multilayer (ML) systems with perpendicular magnetic anisotropy. The spectra depend significantly on the areal density of the antidots. The observed SW modes are qualitatively reproduced by the plane wave method. The interesting results found in our measurements and calculations at small lattice constants can be attributed to the increase of areal density of the shells with modified magnetic properties probably due to distortion of the regular ML structure by the Ga ion bombardment and to increased coupling between localized modes. We propose and discuss the possible mechanisms for this coupling including exchange interaction, tunnelling, and dipolar interactions. © 2014 AIP Publishing LLC.

PubMed | University of Virginia, TU Chemnitz and a Western Digital company
Type: | Journal: Scientific reports | Year: 2016

We report on the out-of-plane thermal conductivities of tetragonal L10 FePt (001) easy-axis and cubic A1 FePt thin films via time-domain thermoreflectance over a temperature range from 133K to 500K. The out-of-plane thermal conductivity of the chemically ordered L10 phase with alternating Fe and Pt layers is ~23% greater than the thermal conductivity of the disordered A1 phase at room temperature and below. However, as temperature is increased above room temperature, the thermal conductivities of the two phases begin to converge. Molecular dynamics simulations on model FePt structures support our experimental findings and help shed more light into the relative vibrational thermal transport properties of the L10 and A1 phases. Furthermore, unlike the varying temperature trends in the thermal conductivities of the two phases, the electronic scattering rates in the out-of-plane direction of the two phases are similar for the temperature range studied in this work.

Li J.,A Western Digital Company | Xu J.,A Western Digital Company | Liu J.,Hitachi Ltd. | Kohira H.,A Western Digital Company
Microsystem Technologies | Year: 2013

A typical thermal-contact sensor (TCS) used in hard-disk drives was investigated by the simulation. Analytical solution to solve temperature variation of sensor due to frictional heat was built to estimate the sensor temperature rise under variable heating power and interference height between the head and disk. To accurately and systematically qualify sensor-temperature distribution and resistance variation under certain variable conditions and sensor time constant, head housing a TCS was modeled by ANSYS commercial software, and thermal-mechanics of TCS coupled with air bearing dynamics was simulated. Simulated results indicated that a TCS with a proper size of 1 μm or less had a maximum resistance variation on friction induced heating to generate a maximum TCS signal output. The sensor-heating maximum protrusion was less that 0.1 nm, and time constant of TCS is about 0.125 μs and its response frequency is about 8 MHz. With a highly accurate measurement system, TCS can detect out asperities of tens of nanometers or less. These results will be helpful in developing and designing thermal-contact sensors for use in hard-disk drives. © 2013 Springer-Verlag Berlin Heidelberg.

Liu J.,Hitachi Ltd. | Liu J.,A Western Digital Company | Xu J.,Hitachi Ltd. | Li J.,Hitachi Ltd.
Microsystem Technologies | Year: 2013

The keep increasing areal density in hard disk drive demands reducing the clearance between the read/write element and the disk surface. A clearance of 2 nm could be achieved using thermal-flying-height technology (Kurita et al. IEEE Trans Magn 41(5):3007-3009, 2005). In such a low-clearance flying regime, it is important to ensure the reliability of the head-disk interface. Head carbon overcoat wear should be taken into account and it requires ultra-smooth disk surface. Conventional method for disk inspection is using glide tester (Nayak et al. IEEE Trans Magn 39(2):729-734, 2003). However, with lower and lower clearance, some small defects on the disk surface can no longer be neglected, and these small defects cannot be detected by glide test. Thus a thermal-contact sensor integrated in a magnetic-head slider was proposed by Shimizu to detect defects on disk surface (Shimizu et al. IEEE Trans Magn 47(10):3426-3432, 2011). Their experimental results confirmed that the contact sensor has equivalent sensitivity for detecting head-disk contact to that of a conventional acoustic emission sensor. And the defect mapping with this method was more sensitive than measurements with an optical surface analyzer. All these results were obtained using experimental method. Thus, numerical simulation studies are necessary in order to investigate the contact mechanics between asperities and the contact sensor. In this paper, a simplified contact model was developed to study contact mechanics between contact sensor and the disk asperity using finite element method. Different parameters' effect on the signal of a contact sensor was investigated. These results are of significance for the development of a thermal contact sensor in the hard disk drive for higher recording density. © 2013 Springer-Verlag Berlin Heidelberg.

Matsumoto T.,Hitachi Ltd. | Akagi F.,Hitachi Ltd. | Mochizuki M.,A Western Digital Company | Miyamoto H.,Hitachi Ltd. | Stipe B.,A Western Digital Company
Optics Express | Year: 2012

We propose a near-field optical transducer using a triangular antenna and a thin film structure (wing) to efficiently generate an optical near-field near a magnetic head. A finite-difference time-domain calculation showed that the near-field was efficiently generated at the apex of the antenna when the dimensions of the wing were optimized for efficient delivery of the surface plasmon excited on the wing to the antenna. The calculated light utilization efficiency (ratio between the absorbed power in the recording medium and the input power) was 8%. The temperature distribution on the mediummagnetic field distributionand magnetization pattern were calculated; the proposed recording head may be capable of an areal recording density of 2.5 Tb/in.2. © 2012 Optical Society of America.

Salo M.,HGST Inc | Olson T.,HGST Inc | Galbraith R.,HGST Inc | Brockie R.,HGST Inc | And 3 more authors.
IEEE Transactions on Magnetics | Year: 2014

The use of a wider writing shingled magnetic recording (SMR) head in spinstand experiments allowed different regions of the SMR track to be analyzed and described. Here, we break the track into curved, best, and trimmed areas. The curved area is written with the writer edge, which has high curvature and poor write field gradient, resulting in low resolution and high noise. The trimmed region is defined by head fields combining with disk demagnetization fields. Together these fields attack the low frequency magnets, boosting resolution, increasing noise, and generating a narrow out of phase copy of the trimmed track (the negative sliver). This is explained via measurements and modeling. We also explain the measured magnetic write width dependence on linear density based on the frequency response of the reader as well as writer and media effects. We employ linear deconvolution to extract the binary impulse responses of the SMR data track and its neighboring tracks to characterize intertrack interference. The writer and media effects, which give rise to the negative sliver observed, are shown to explain the interference behavior with linear density. © 2014 IEEE.

Gong X.,University of Pittsburgh | Kozbial A.,University of Pittsburgh | Rose F.,A Western Digital Company | Li L.,University of Pittsburgh
ACS Applied Materials and Interfaces | Year: 2015

In the current paper, AFM studies were conducted on nanometer-thick ionic liquids (ILs) confined to an amorphous carbon (AC) surface, which is critical to the design of the next-generation media lubricant for hard disk drives (HDDs). The results indicated that the existence of the delocalized ring in the cation is critical to layering of ILs. Extended layering was observed only when there is imidazolium ring in the cation. When the imidazolium ring is replaced by an aliphatic moiety, "drop-on-layer" (dewetting) structure was observed. On the basis of the experimental results, we proposed that π-π+ stacking between sp2 carbon in the AC and the imidazolium cation in the ILs is the key to the extended layering of ILs at the ILs/AC interface. © 2015 American Chemical Society.

Jia Q.,A Western Digital Company | Cao S.,A Western Digital Company | Guo G.,A Western Digital Company | Yu J.,A Western Digital Company
IEEE Transactions on Magnetics | Year: 2013

A novel control method with an add-on nonlinear feedback controller is proposed in this paper to work together with the existing linear controller to deal with external disturbance in hard disk drive (HDD) systems. In the proposed control scheme, the capability of disturbance rejection is boosted when the tracking error of the control system gets larger due to the external disturbances. The stability of the proposed scheme has been proved, and chassis tests on several commercial notebook PC models showed that the proposed method is effective to handle wide-band vibration. Moreover, the implementation of the proposed scheme is very simple and may be even simpler than the linear controller. © 1965-2012 IEEE.

McCallum A.T.,A Western Digital Company | Kercher D.,A Western Digital Company | Lille J.,A Western Digital Company | Weller D.,A Western Digital Company | Hellwig O.,A Western Digital Company
Applied Physics Letters | Year: 2012

We investigated different fabrication methods for (002) textured high anisotropy L1 0-FePt thin continuous films. While depositing at elevated temperature or post-annealing yields discontinuous or very rough films unsuitable for bit patterned media (BPM) fabrication, post-annealing with an additional SiO 2 cap layer results in smooth continuous L1 0-FePt thin films that can be used for patterning. The SiO 2 layer can be removed after annealing without significantly damaging the FePt, thus allowing additional deposition of lower anisotropy layers for forming exchange coupled composite or other layered BPM structures. © 2012 American Institute of Physics.

Nakatani T.M.,A Western Digital Company | Childress J.R.,A Western Digital Company
Journal of Applied Physics | Year: 2015

We have investigated electrically conductive indium-zinc-oxide (IZO) deposited by magnetron sputtering as spacer layer for current-perpendicular-to-the-plane giant magnetoresistance sensor devices. Spin-valves with a Co50Fe50/IZO/Co50Fe50 trilayer showed resistance-area product (RA) ranging from 110 to 250 mΩ μm2, significantly larger than all-metal structures with Ag or Cu spacers (∼40 mΩ μm2). Magnetoresistance ratios (ΔR/R) of 2.5% to 5.5% depending on the IZO spacer thickness (1.5-6.0 nm), corresponding to ΔRA values from 3 to 13 mΩ μm2, were obtained. The values of ΔRA with the IZO spacers and Co50Fe50 magnetic layers were significantly larger than those with conventional metal spacers and Co50Fe50 magnetic layers (∼1-2 mΩ μm2). The dependence of ΔRA on the magnetic layer thickness suggests that the larger ΔRA obtained with IZO spacer is due to a large interfacial spin-dependent scattering caused by the large specific resistance at the Co50Fe50/IZO interface. From structural characterization by TEM and the observed dependence of the RA dispersion on device size, the electric current flowing through the IZO spacer is thought to be laterally uniform, similar to normal metal spacers. © 2015 AIP Publishing LLC.

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