A comparative analysis of the writability of trailing pole (TP) and leading pole (LP) writers on double-layer perpendicular media was done by three-dimensional finite-element method modeling. The writability of the writers was estimated by a maximal strength of effective write field that was defined by the Stoner-Wohlfarth model. The LP writer revealed a weaker perpendicular but stronger longitudinal component of the write field and bigger write angle. The longitudinal component and write angle minimize the difference in writability between the two writer designs. The writers showed a different writability dependence on initial permeability and saturation flux density of a soft magnetic keeper. An increase of the keeper permeability improves the writability of the TP writer but marginally affects performance of the other. Modeling results suggest that the LP writer might outperform the writer with the TP if the keeper permeability is below 100. The TP writer did not show a noticeable sensitivity to the saturation flux density of the keeper in a range from 10 to 24 kG. The writability of the LP writer decreases monotonically with the saturation flux density of the keeper. Received results imply that the TP and LP writers might have different requirements to properties of the keeper material.
The dependence of the giant magnetoresistance (GMR) on the thickness of the Co layers in Co/Cu multilayers was investigated experimentally. The thickness of the Cu layer was held constant at tCu=19 Å, which corresponds to the second maximum of the GMR ratio oscillating dependence on tCu. The Co layer thickness was varied from 4.8 to 79.0 Å. High resolution transmission electron microscopy showed the existence of the two-dimensional artificial superstructure with defined periodicity as well as sharp and flat interfaces. From wide angle x-ray diffraction it was concluded that at Co layer thickness below 40 Å the multilayers are polycrystalline with mainly fcc lattice structure and (111) texture. In the case of thicker Co layers indications of hcp Co could be found. The GMR ratio reaches a maximum at Co layer thickness about 11 Å. It was shown that the GMR in sputtered Co/Cu multilayers is due to spin scattering at the interfaces and resistance is strongly influenced by interface scattering.
Tunneling magnetoresistive (TMR) readers capable of 150 Gb/in 2 of areal density magnetic recording for hard disk drive were demonstrated with bit-error-rate performance. The head design used is basically a bottom type stack of Ta/PtMn/CoFe/ Ru/CoFe/oxide barrier/CoFe/NiFe/Ta cap with abutted hard bias stabilization. The electrical reader width is about 4 to reach a very high track density and shield-to-shield spacing is about 700 A for high linear density. On-track bit error floor is better than 10 5 at a linear density of 900 KBPI and the recording system noise is dominated by the media. The best areal density achieved (using 4 OTC reference level) is 143 Gb/in 2 using symmetric squeeze and 152 Gb/in 2 using asymmetric squeeze method, respectively. It was found that the TMR head has several decibels more signal-to-noise ratio gain over spin valve readers at 150 Gb/in 2 and beyond. The TMR head is also suitable for perpendicular recording application.Index Terms-Areal density, current-perpendicular-to-plane (CPP) geometry, perpendicular recording, signal-to-noise ratio (SNR), tunneling magnetoresistive (TMR) heads.
The effect of magnetic anisotropy constants and inter-granular exchange coupling on properties of hcp CoCrX perpendicular media was studied by micromagnetic modeling. It was found that the second anisotropy constant K2 reduces the energy barrier, coercivity HC, saturation field HS and, as a result, promotes writeability of the media for fixed anisotropy field HK. HC inversely decreases with the increase of K2/K1 ratio. Exchange coupling modifies a domain structure of the media in a virgin state and slope of hysteresis loop by reducing the coercivity and saturation field, and marginally increasing the nucleation field. Magnetic domains were found even in the decoupled media. The minimal domain size is about 2.5⋅dG, where dG is an average grain size of the media. The domain size increases exponentially with the inter-granular exchange. The transition parameter and dc noise is reduced with increased exchange coupling. At a specific exchange coupling the dependence of the transition parameter on the exchange almost disappears, approaching a minimum value of dG/3.
An effect of the write field gradient on perpendicular recording has been studied by three-dimensional finite-element method and micromagnetic modeling. Two conceptual writer designs were compared: the conventional trailing pole (TP) writer with the main pole serving as the trailing pole and the leading pole (LP) writer, where the main pole operates as the leading pole. Both writers record transitions on double-layer media by the trailing edge of the main pole. The LP writer allows effective control of the write field gradient by positioning the trailing edge adjacent to the write gap. The dependencies of the perpendicular HPERP and longitudinal HLONG components of the write field along with a gradient of the perpendicular component HPERP/dx and write angle on write gap length g and write current IW were computed. The LP writer revealed higher HPERP/dx than the TP writer at g⩽2 μm. The HPERP/dx has a maximum at IW=15–20 mA for both writers and decreases with the current increase. The LP writer exhibited higher HPERP/dx and write angle Θ, as well weaker dependence of these parameters on write current than the TP writer in all ranges of current. Micromagnetic modeling of recorded patterns has shown that the LP writer provides better writeability, and a sharper and less curved transition. Both writers demonstrated the best performance at IW=15–20 mA where HPERP/dx and the write angle have the maximum. Severe transition distortion was observed for the TP writer at IW>30 mA.
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