Randall Victora, Principal Investigator

Micromagnetic Simulations Including Thermal Fluctuations

Current magnetic recording technology has approached several new technical barriers that may limit the further increase of hard disk recording density. Examples of these barriers include fundamental limitations in the thermal stability and switching speed of the magnetic domains. Instead of the current longitudinal recording method, one of the alternatives has been to record the media perpendicularly, which, however, may require significant technological changes.

These researchers have developed a micromagnetic model that simulates the characteristics of perpendicular recording media and recording heads, and have already demonstrated the accuracy of the media simulation. They are now using the model to solve two important problems. The first is the prediction of hysteresis loops for materials exhibiting defects and strongly exchange-coupled grains. The second problem is the design of a recording head that can develop adequate field, gradient and switching speed to be useful at densities of a terrabit/inch2. Both of these problems require large computational resources either because the sample region must be finely divided (the media problem) or because the sample region must be relatively large (the head problem).

Another, related topic of research for this group is micromagnetic predictions of bit decay caused by thermal fluctuations over long time scales. Thermal decay in magnetic recording media increases with time, consequently decreasing the signal-to-noise ratio. The new scaling technique was used to predict bit decay over long time scales. An ideal square-wave field was used to record bits in thin film magnetic recording media. Comparison of bit thermal stability for longitudinal and perpendicular thin film media with similar KuV/kT was carried out at recording densities from 50 to 400 Gbit/in2. Bit decay in a Co/Pd superlattice film at ~80 Gbit/in2 was studied as well.

Research Group

Mohammed Patwari, Graduate Student Researcher
Jianhua Xue, Graduate Student Researcher