Yong-su Kim

Head design scheme for perpendicular recording with single layered media

For ultra high areal recording density, we suggest the perpendicular recording scheme with ring head and single layered media for easy implementation. To improve the perpendicular head field and its gradient, conventional ring head is modified by cutting the top pole edge. Head field was calculated with nonlinear finite element method. The write process was simulated with micromagnetics using the calculated head field of two heads (original and modified) at each magnetic grain of recording disk, instead of using Karlqvist head field. Both simulated and measured MFM images show that the transition of modified head is clearer than original one. Also, TAA and SNR of modified head are higher than results of original head. With simple modification, currently used ring head can be easily applied to high density perpendicular recording HDD system.

Multibit MRAM using a pair of memory cells

Magnetic random access memory (MRAM) is one of the most promising candidates to provide energy-efficient and nonvolatile memory. We present a new MRAM design using a pair of cells where each cell can store two bits of information. The pair cells have a parallelogram shape to induce broken-shape magnetic anisotropy along the short axis of the cell. One important advantage of the pair cells is that they can share the same word- and bit-lines intersection in the MRAM architecture. This means that the number of electrical current lines can be reduced and lead to higher recording density. Such design is successfully demonstrated using finite-element micromagnetic simulation.

Optimal Side Shield Write Head Design for Ultra-High Recording Density

In magnetic writing heads, one of the most important factors for ultra-high recording density is the skirt width of write field along cross track direction without degradation of head field and field gradient. The side shield design is known to be the most powerful design for reducing the skirt width. However, the side shields reduce write field and field gradient weak. By finite-element method simulation, we propose the floating (separated) side shield to reduce skirt width without field degradation of write head. As a result, we were able to reduce skirt width from 350 to 250 nm with almost no head field degradation. In addition to increasing the recording density, the separated side shield design provides other benefits to head fabrication by reducing the topography of wafer process. We used design of experiment (DOE) tools, especially response surface method (RSM), to optimize the design. In the simulation, we took into account all soft magnetic materials (write head and soft magnetic underlayer). To verify the results, we checked the correlation between the head field of each shape and adjacent track encroachment (ATE).

New Type Side Shield Head for Ultrahigh Density Recording

In magnetic writing heads, one of the most important factors for ultrahigh recording density is the skirt width of write field along cross track direction without degradation of head field and field gradient. The side shield design is known to be the most powerful design for reducing the skirt width. However, the side shields make write field and field gradient weak. By FEA simulation, we propose the shell type side shield to reduce skirt width without field degradation. As a result, we could reduce track width from 255 to 190 nm with no head field degradation, at 7060 Oe. We used design of experiment (DOE) tools, especially response surface method (RSM), to optimize the design. In the simulation, we took into account all soft magnetic materials (write head and soft magnetic underlayer). To verify the results, we checked the correlation between the head field of each shape and ATE.

Simulation of the Effect of Soft Underlayer Domain Wall Structure on Output Signal in Perpendicular Magnetic Recording

Controlling magnetic domains in soft underlayer (SUL) of perpendicular magnetic recording (PMR) is an important issue for the application of PMR in HDD. We studied the magnetic domain structures in SUL using the finite element based micromagnetic simulation (FEMM) for the SUL models with different thicknesses. The purpose is to simulate the magnetic domain wall noise when the SUL thickness and saturation magnetization are changed. The simulation results show that a 15 ㎚ SUL forms simpler Neel wall domain wall pattern and 40 ㎚ SUL forms complex Bloch wall. To visualize the effect of these domain walls stray field at a read sensor position, the magnetic stray field of the domain walls at air bearing surface (ABS) which is 50 ㎚ above the SUL was simulated and the results imply that Bloch walls have stronger stray field with more complicated field patterns than Neel walls and this becomes a significant noise source. Therefore, the thickness of the SUL should be controlled to avoid the formation of Bloch walls.

Dynamic recording property simulations of perpendicular magnetic recording with ring head and single layered media

Summary form only given. Perpendicular magnetic recording is one of the promising candidates of the next-generation magnetic recording system for ultra high recording density. Perpendicular magnetic recording with a ring head and single layered media has strong merits because of its easy implementation in conventional hard disk technology. In spite of these small changes, the perpendicular recording system shows quite different dynamic recording behavior when compared with the longitudinal system because the media demagnetization field has an opposite effect.

Simulation of writing head in perpendicular magnetic recording system

For perpendicular magnetic recording system, we suggest the modeling scheme combining finite element method and the fine field analysis. We did not use the Karlqvist head field but simulated a head field by the finite element method with precise simulation. For this purpose, we developed a Laplace program to calculate the head field at micromagnetic domains. We simulated the write process for a conventional head with a single layer perpendicular media and compared magnetic force microscopy images of simulated written bit patterns and tested patterns.