Alexander M. Shukh

Use of a permanent magnet in the synthetic antiferromagnet of a spin-valve

A spinvalve using a permanent magnet as the pinned layer in a synthetic antiferromagnet of a spinvalve is described here. Permanent magnet materials can have the following advantages over antiferromagnetic materials: superior corrosion resistance, a large switching field even at relatively high temperatures, and not needing a high temperature anneal to set its magnetic orientation. The giant magnetoresistance, high field switching, and switching at high temperatures was investigated for various spinvalves using the following film stacks as the pinned layer: CoCrPt (CCP); CCP\CoFe, CCP\Ru\CoFe; and CCP\CoFe\Ru\CoFe. It was found that a thin CoFe layer between the CCP and Cu and between the CCP and Ru enhances giant magnetoresistance and antiferromagnetic coupling, respectively. When the CCP is used in a synthetic antiferromagnet, the CCP coercivity increases compared to a single layer of CCP. The switching field of CCP at 425 °C is >1000 Oe, at the same temperature the switching field for an antiferromagne...

Writability of perpendicular recording heads

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.

Micromagnetic modeling of low noise perpendicular media

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 ...

Write field gradient effect on perpendicular recording

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 h...

Stray field sensitivity of perpendicular recording heads

An effect of stray field on perpendicular head performance was studied by three-dimensional finite-element method modeling. Perpendicular writers in a drive are exposed to the stray field up to 20 Oe, which generates an erase field in double layer media. The coefficient of a stray field magnification by writer can be of several dozens. Main and return poles of the writer generate the same polarity erase field in the media but the field is stronger under the main pole due to considerably smaller pole size at an air-bearing surface (ABS). The erase field depends on parameters of the media such as keeper permeability μK and head-keeper spacing (HKS) but is not sensitive to keeper thickness. The erase field exhibits a maximum at μK≈20 and decreases with μK or HKS increase. An incident angle of the stray field relatively to a medium plane substantially affects the field strength exhibiting a maximum at about 30° from normal for conventional single pole writer. The recess of the return pole from the ABS causes ...

Effect of Storage Layer on Writeability of a Perpendicular Magnetic Recording Head

The effect of the storage layer on the writeability of a magnetic head for perpendicular recording was studied through micromagnetic and finite-element-method modeling. The results suggest that the permeability of the storage layer of double-layer perpendicular recording medium monotonically increases with the intergranular exchange. Increase of the storage layer permeability improves the writeability of the single-pole recording head and the gradient of the write field in the storage layer.

Storage Layer Effect on Writability of Perpendicular Recording Head

Micromagnetic and 3D FEM modeling were used to study the storage layer effect on writability of perpendicular magnetic recording head. The magnetic hysteresis loops of the perpendicular storage layer were obtained. The effect of intragranular exchange on storage layer permeability and the latters effect on the perpendicular component of the write field were also investigated.