Micromagnetics

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Magnets are prevalent throughout daily life:
– Cars contain magnets in starter motors, electric windows, and door-locking systems
– Kitchens have magnetic motors in refrigerators, microwave ovens, and washing machines
– Entertainment systems: video recorders, CD/DVD players, and audio tape recorders
– Televisions and monitors use magnetics to deflect and position electron beam used to create an image
– Electric bells in telephones, alarms, and doorbells contain magnetic ringers
– Medical applications: magnetic fluids in eye surgery and drug delivery, prosthetics, cancer therapy, and magnetic resonance imaging
– Credit cards, cooling fans, power station generators, audio speakers
– Data storage in computers – hard disk drives!

For hard disk drive manufacturers, greater areal density corresponds to greater storage capacity. Present methods of hard disk production are approaching physical limits and sooner it will not be possible to increase capacity. Micromagnetics studies the behavior of magnets at microscopic scales and involves the research of novel materials and designs to improve modern hard disks.

Static micromagnetics: minimizing magnetic energy and finding the magnetization direction vector everywhere

Four competing terms:

Exchange energy: favors configurations where the magnetization varies slowly across the sample

Anisotropy energy: directional dependence of a material’s magnetic properties, favors magnetic configurations where the magnetization is everywhere aligned along an easy axis

Zeeman energy: interaction energy between magnetization and any externally applied field, favors alignment of the magnetization parallel to the applied field

Demagnetizing field: magnetic field created by the magnetic sample upon itself, favors magnetic configurations that minimize magnetic charges

Dynamic micromagnetics: predicting time evolution of the magnetic sample by solving the Landau-Lifshitz-Gilbert equation: