K. J. Lee

Kink-free design of submicrometer MRAM cell

Full micromagnetic simulations have been performed to investigate the origin of a kink in a magnetoresistive curve and to design a kink-free magnetoresistive random access memory (MRAM) cell. The kink in an at-field curve can originate from the 2/spl pi/-wall or the vortex formation, which is strongly dependent on the magnetic properties and the geometry of a free layer. The kink originating from the 2/spl pi/-wall formation was found to disappear in a remanent magnetization curve; therefore, it should not affect the selectivity of a MRAM array. It turned out that the vortex formation was the major origin of the kink when the free layer has the high saturation magnetization and the thick layer thickness. This vortex state is a local minimum state even after removing the external field. Finally, we found kink-free criteria for various saturation magnetizations, thicknesses, and aspect ratios of a free layer.

Transition and DC noise characteristics of longitudinal oriented media

Transition and DC noise characteristics of longitudinal recording media were studied as a function of orientation ratio (OR). With increasing OR, a substantial decrease of DC noise is observed against the gradually increasing transition noise, resulting in the reduced media total noise. The increase in the media transition noise with OR is attributed to the increase in the cross-track correlation length s. The experimentally estimated s for the media with OR=1.8 is significantly larger than that of the media with OR=1.25, possibly resulting from the difference in magnetostatically coupled Co grains aligned to the track direction. For high-density low M/sub r/t designs, reducing DC noise by increasing OR, in spite of an increase in transition noise, becomes an effective means to increasing areal density.

Magnetic and recording characteristics of perpendicular magnetic media with different anisotropy orientation dispersions

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 Δθ50 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.

New design of perpendicular magnetic recording media: hybrid media

To achieve both the high anisotropy energy and high SNR performance at ultra high areal recording density, we have studied paired recording layered PMR media named as hybrid media. Hybrid media consist of 1/sup st/ recording layer and 2/sup nd/ recording layer. 1/sup st/ recording layer and 2/sup nd/ recording layer have low noise properties and high anisotropy energy, respectively. 1/sup st/ and 2/sup nd/ recording layer are continuously and coherently stacked on the top of the underlayer.

Kink-free design of submicron MRAM cell

In this work, full micromagnetic simulations with comparing experimental measurements have been performed for broad range of Ms (400/spl sim/1600 emu/cm/sup 3/), thickness of free layer (1/spl sim/5 nm) and aspect ratio of MRAM cell (1.5/spl sim/3). We used cell with round edge, since perfect rectangular or elliptical shape is hardly obtained from conventional lithography technology. For the round cell, edge radius was 80 nm and short width was 0.2 /spl mu/m.

The effect of hybrid media to achieve both good thermal stability and excellent read/write performance

In this paper, hybrid media to achieve both good thermal stability and excellent read/write performance were analyzed. Hybrid media consist of 1/sup st/ recording layer having low noise properties and 2 /sup nd/ recording layer having high anisotropy energy.

Step-like energy barrier variations of high K/sub u/ material

Summary form only given. In this work, we have focused on the rotation mode and the energy barrier of material with K/sub u/ larger than 10/sup 7/ erg/cm/sup 3/. The Landau-Lifshitz-Gilbert equation was solved to find the mode. To consider incoherent mode properly, a magnetic grain was subdivided into lots of cubic cells with volume of (1 nm)/sup 3/. The energy barrier was determined as the maximum energy difference during switching.

Ti grain cutting layer and Pt underlayer for CoCr based single magnetic layered perpendicular magnetic recording media

Summary form only given. For CoCr based perpendicular magnetic recording (PMR) disks, a Ti underlayer has been commonly used because it is known to improve the c-axis preferred orientation of the recording media. However, it has also been reported that a magnetically unstable initial layer exists between the Ti underlayer and the CoCr based recording layer because of large lattice mismatch between Ti and the recording layer. In this work, we propose a new underlayer structure composed of Ti/Pt double layers for a CoCrPtX magnetic film, which was found to successfully reduce the grain/domain size and exchange coupling in the recording layer, maintaining excellent c-axis preferred orientation of the film.