Johannes van Ek

The Physics of Ultra-High-Density Magnetic Recording

1 Introduction to Micromagnetic Recording Physics.- 2 Microstructure of Longitudinal Media.- 3 Magnetization Dynamics and Thermal Fluctuations in Fine Grains and Films.- 4 Measurement of Dynamic Properties in Thin-Films.- 5 Thermal Effects in High-Density Recording Media.- 6 Dynamic Effects in High-Density Recording Media.- 7 Patterned Media.- 8 Perpendicular Recording Media.- 9 Self-Assembled Magnetic Nanoparticle Arrays.- 10 Theory of Magnetotransport for Magnetic Recording.- 11 Recording Head Design.

Giant magnetoresistance properties of patterned IrMn exchange biased spin valves

Giant magnetoresistance (GMR) responses were studied in micron-sized IrMn pinned spin valve stripes. As the stripe height is decreased both the pinning field and free layer bias field increase while the GMR ratio stays almost constant. The free layer coercivity becomes zero for the shortest stripe while the pinned layer coercivity drops slightly at high aspect ratio. The pinned layer switching field is enhanced in the patterned films, indicating a strong magnetostatic coupling between the free and pinned layer that was further simulated micromagnetically.

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 ...

Variation of magnetoresistive sensitivity maps of patterned giant magnetoresistance sensors

A scanning probe microscope which combines probe contacts for the supply of current with a magnetic force microscope (MFM) for fully automated imaging of electrically active, patterned sensor-like devices across a wafer was developed. This was used for magnetoresistive sensitivity mapping (MSM) of giant magnetoresistive sensors with different stabilization schemes. Multiple measurements of sensors showed that the MSM images were very repeatable. The complex image patterns varied significantly from sensor to sensor across a wafer. With MFM tips magnetized perpendicular to the ferromagnetic films in the sensor, MSM signals at the top and bottom of the sensor were significantly more intense than signals at the sensor interior. Results from micromagnetic calculations were found to be consistent with the experimental observations.