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ABSTRACT: A systematic investigation of the magnetic and recording characteristics of reactively sputtered CoPtCr-(Si-O, Ti-O, Cr-O) media has been performed. The optimum oxidation condition for media with well-isolated Co grains, high coercivity (H<sub>c</sub>) and nucleation field (H<sub>n</sub>), and superior media noise performance strongly depends on the oxide type. Despite differences in the optimum oxidation condition, the highest achievable H<sub>c</sub> and H<sub>n</sub> are similar. The transition jitter and magnetic write width are mainly determined by the magnetic exchange coupling depending on the oxidation condition but not by the oxide type
IEEE Transactions on Magnetics 11/2006; · 1.36 Impact Factor
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ABSTRACT: Magnetic patterns on perpendicular recording media were imaged by spin-stand level dynamic read-back microscopy. High-density tracks are clearly resolved up to 1000 kfci and details of magnetic bit structure, not usually observable using standard read-write tests, are readily observed. Encroachment of tracks on Co-Cr-Pt-O media with low oxygen content and low-coercivity results in a nonuniform erasure; as-written rectangular bits become trapezoidal in shape. Media with high oxygen content and high coercivity provide superior side erasure resistance
IEEE Transactions on Magnetics 11/2006; · 1.36 Impact Factor
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ABSTRACT: A spin-stand level dynamic read-back microscopy (DRM) technique offers ease of use and full compatibility with standard media parametrics testing. We designed and implemented a DRM tester based on a LeCroy DDA5005 oscilloscope and a Guzik spin-stand. Using a DRM, we investigated the effect of magnetic exchange coupling on side erasure of CoCrPt-SiO PMR media. Exchange was controlled by varying the oxygen partial pressure during deposition. The paper show tracks after a progressive edge-trimming from the both sides using a low DC-negative erase current.
Magnetics Conference, 2006. INTERMAG 2006. IEEE International; 06/2006
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ABSTRACT: A systematic investigation of the structural and recording characteristics of CoPtCrO composite media with various Co alloys as well as continuous TbFeCo capping layers has been performed. For the media with a Co-alloy capping layer (M<sub>s</sub>∼900 emu/cm<sup>3</sup>), the transition jitter remains unaffected and dc noise is greatly reduced. However, for the media with low M<sub>s</sub> capping layer or continuously exchange coupled TbFeCo capping layer, transition jitter is increased. Magnetically continuous but structurally discontinuous Co-alloy capping layers grown onto well-isolated Co grains can reduce dc noise, while maintaining low transition noise.
IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
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ABSTRACT: The permeability of the magnetic soft underlayer (SUL) was systematically varied through SUL structure change, and its effect on wide area adjacent track erasure (ATE) and media overwrite (OW) was studied. Results suggest that ATE decreases with SUL permeability, and it involves only a finite thickness of the SUL. OW increases with SUL permeability as well as SUL thickness. In addition, ATE is less affected by magnetic spacing than OW. Antiparallel coupled SUL (APS) improves ATE. A double-APS structure with a permeability gradient is proposed to optimize OW and ATE performance.
IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
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ABSTRACT: An anisotropy enhanced dual magnetic layer structure is proposed to improve the recording performance of perpendicular media. The initial layer is made of low noise Co-Cr-Pt-O layer and the top layer is made of higher anisotropy Co-Cr-Pt-B layer. A higher nucleation field than the single layer structures is obtained for the dual magnetic layer media. By optimizing the layer structure and properties, better signal-to-noise and lower adjacent track erasure can be achieved for the dual magnetic layer design over single magnetic layer media.
IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
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ABSTRACT: We discuss a method of ac-demagnetizing an entire disk using permanent magnets and compare the demagnetized states of perpendicular media with different levels of intergranular exchange. The method consists of applying a large field perpendicular to the media recording layer anisotropy direction. This bulk ac-erasure technique provides a background noise that is lower than that which can be achieved by ac-erasing with a write head. Highly exchange-coupled media exhibit low dc noise but increased ac-erased background noise. Magnetic force microscopy data show increased magnetic roughness in the ac-erased state with exchange-coupling strength. For the media with least coupling the dc noise is similar to the ac noise.
IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
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ABSTRACT: A systematic investigation of the magnetic and recording characteristics of CoPtCrO media with different Co grain magnetic anisotropy orientation dispersion (AOD) is performed. AOD is characterized by Δθ<sub>50</sub> of the x-ray diffraction Co peak. AOD was systematically varied between 3.3° and 10.5° by varying the growth condition of Ru layer. With increasing AOD, more grain-boundary segregation occurs, resulting in reduced exchange coupling. Micromagnetic simulation and experimentally measured time dependence of coercivity indicate that magnetic switching of well-isolated Co particles is affected by exchange coupling strength as well as Co AOD. Higher coercivity, narrower switching field distribution, and good thermal stability are achieved with lower Co AOD. Reduced Co AOD leads to a substantial decrease of both transition jitter and dc noise.
Journal of Applied Physics 06/2005; · 2.17 Impact Factor
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ABSTRACT: Adjacent track erasure (ATE) is investigated for longitudinal recording media with different remanent magnetization and thickness product. The dynamic switching field Hcrp for moment fraction p is found to be a good indicator of signal erasure due to ATE. Given the head fringing field, Hcrp curves can be used to predict ATE for long exposures. Conversely, from the signal degradation of neighboring tracks due to ATE, the average fringing fields at a particular distance from the write head can be estimated.
Journal of Applied Physics 05/2005; 97(10):10P109-10P109-3. · 2.17 Impact Factor
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Magnetics Conference, 2000. INTERMAG 2000 Digest of Technical Papers. 2000 IEEE International; 05/2005
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Magnetics Conference, 2000. INTERMAG 2000 Digest of Technical Papers. 2000 IEEE International; 05/2005
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ABSTRACT: The effect of magnetic "preconditioning" on the recording performance of perpendicular media is investigated. Furthermore, the dependence of the magnetic write width (MWW) of shielded-pole heads (SPH) on soft-underlayer (SUL) type and thickness (t<sub>SUL</sub>) and the recording performance of perpendicular media with thin SULs are examined. The MWW dependence on SUL structure is influenced by the pole-to-trailing shield spacing. For a wide-gap (∼80 nm) SPH, thick single-layer, SULs are preferred. For a narrow-gap (∼50 nm) SPH, MWW is less sensitive to the SUL type. For both narrow and wide-gap SPH and for media with an antiferromagnetically-coupled SUL, MWW is reduced for t<sub>SUL</sub><100 nm. Comparable performance is achieved relative to media with t<sub>SUL</sub>∼150 nm.
IEEE Transactions on Magnetics 03/2005; · 1.36 Impact Factor
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ABSTRACT: A promising soft magnetic under layer (SUL) structure consisting of anti-parallel coupled soft layers (APS) is investigated to improve the performance of high-density perpendicular recording media. CoCrPt-O recording media with average grain diameter ∼6 nm, coercivity of 5 kOe and nucleation field of -2 kOe is fabricated on both conventional SUL and APS. Wide-area adjacent track erasure (ATE) is observed for conventional SUL, which increases at lower interlayer spacing (t<sub>IL</sub>). APS structure enables the suppression of ATE even up to t<sub>IL</sub>=10 nm. Moreover, APS leads to reduced dc erase noise and improved signal to noise ratio particularly for SUL thicknesses <100 nm.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
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ABSTRACT: Compositionally graded magnetic multilayer (CGM) structures were investigated to improve media signal-to-noise ratio (SNR) as well as thermal stability. The medium structure consists of multiple magnetic layers that play an important role in determining the crystallographic texture as well as magnetic activation volume. Low medium noise is achieved while retaining high resolution, as the number of layers is increased. The CGM media offer a magnetic anisotropy gradient from the top to bottom layers, which enhances head writability at high frequencies without affecting thermal stability. Improved magnetic and recording properties such as high K<sub>u</sub> V/kT, SNR, and overwrite are obtained with CGM media, suitable for high areal density recording.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
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ABSTRACT: Antiferromagnetically coupled (AFC) media and conventional media (CM) were compared side to side over a wide range of orientation ratios (OR). For both AFC and CM, oriented media outperform isotropic media. AFC and CM show similar signal-to-noise ratios (SNR) throughout the entire range of OR. CM exhibit good SNR performance even at M<sub>r</sub>t<0.33 memu/cm<sup>2</sup> but with unacceptable thermal decay. When the coercivity is increased to match that of AFC at M<sub>r</sub>t<0.30 memu/cm<sup>2</sup>, the SNR of the CM deteriorates and the thermal stability is still worse than the AFC. AFC offers some advantages in SNR roll-off in the isotropic media but not in the highly oriented media.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
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ABSTRACT: We have studied the percolation limit of synthetic ferrimagnetic media (SFM) by the measurement of noise power and third harmonic ratio and by imaging with a high-resolution magnetic force microscope (MFM). The noise power spectrum, which helps to find the onset of percolation, is significantly different in SFM structures compared to the conventional recording media. Properties of the stabilization layers, such as switching field distribution (SFD), are highly influential in deciding the integrated noise power spectrum. With suitable selection of high moment stabilization layers, the noise at higher densities, within the percolation density limit, can be substantially reduced. Third harmonic ratio studies indicate that the partial erasure occurs above ∼900 kfci. Using a high-resolution high-Q MFM, it is possible to obtain stable and nonpercolating high density patterns up to 1000 kfci on media with tBr=0.22 memu/cm<sup>2</sup> and Hc∼4500 Oe. This results in practical designs of media for recording densities >150 Gbits/in<sup>2</sup>.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
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ABSTRACT: Synthetic ferrimagnetic media comprised of two magnetic layers tend to exhibit larger nonlinear transition shift (NLTS) compared to single magnetic layer conventional media. NLTS is reduced by increasing the antiferromagnetic exchange field (H<sub> ex </sub>) and especially by employing a lower layer with high magnetization and thickness product (M<sub>s</sub>t) . Due to the lower switching field of the stabilization layer, the position of the transition during writing is farther downstream than that of the upper layer. We suggest that, at high densities, the pinning of the lower layer transition below the nearest neighboring upper layer transition leads to a reduction of demagnetizing fields and therefore NLTS.
Applied Physics Letters 08/2004; · 3.84 Impact Factor
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ABSTRACT: The effect of oxygen incorporation on the crystallographic, magnetic, and recording performance of perpendicular magnetic recording (PMR) oxide media was investigated. The media were prepared by dc-magnetron sputtering of CoCrPt-SiO<sub>2</sub> targets in an Ar/O<sub>2</sub> gas mixture. X-ray photoelectron spectroscopy (XPS) detected Cr-O peaks in the sputtered film, whereas no strong evidence of SiO<sub>2</sub> is seen. Moderate oxygen incorporation in the film (∼15 at%) promotes Cr-O formation in the grain boundary and results in a dramatic increase of coercivity H<sub>c</sub> and signal-to-noise ratio (SNR). However, as the O<sub>2</sub> content is further increased, oxide incorporates into the core of the grains, resulting in decreased H<sub>c</sub>, magnetization and SNR.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
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ABSTRACT: The thermal stability and read-write properties of synthetic ferrimagnetic media (SFM) are compared with conventional media (CM) of the same stability factor KuV/kT and Mrδ (remanent magnetization and thickness product). SFM are found to be more stable than the equivalent CM, suggesting that the thermal stability advantage does not arise simply from an "increased effective volume." The overwrite properties (OW) and nonlinear transition shift (NLTS) are better for CM. However, for media with the same signal decay rate, the OW is similar over a wide head field range and the NLTS match at larger fields.
IEEE Transactions on Magnetics 10/2003; · 1.36 Impact Factor
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ABSTRACT: Signal-to-noise ratio (SNR) and thermal stability issues are addressed to evaluate synthetic ferrimagnetic media (SFM) for achieving areal densities >100 Gb/in<sup>2</sup>. Thermally stable SFM is obtained at M<sub>r</sub>δ values as low as 0.15 memu/cm<sup>2</sup>, utilizing a higher magnetic anisotropy for the stabilization magnetic layer. The SNR relations for SFM are decided by the effective M<sub>r</sub>δ and coercivity, similar to conventional media. The recording characteristics of a low M<sub>r</sub>δ medium was compared with a higher M<sub>r</sub>δ medium used for the 106-Gb/in<sup>2</sup> demonstration. Lower medium noise and higher signal resolution of the lower M<sub>r</sub>δ medium indicate an areal density extension to beyond ∼150 Gb/in<sup>2</sup>.
IEEE Transactions on Magnetics 04/2003; · 1.36 Impact Factor
