Length and time scales in magnetism
Modern magnetic materials are structured on the nanometre lengthscale to achieve the desired magnetic behaviour. For example, a computer hard drive records information on a storage layer comprised of magnetic grains around 7-8nm in diameter. Information is read back using magnetic sensors which contain films on the order of 10 atoms thick. Magnetism on this lengthscale, in complex magnetic structures, is a challenging theoretical and experimental problem. Additionally, magnetism poses a difficult problem in terms of the timescales of interest. Currently, experiments using high energy lasers are investigating magnetic properties on a femtosecond timescale. This is an important frontier in solid state physics. At the same time, the data stored in a hard drive must be stable for at least 10 years. Consequently we have to consider dynamic magnetisation processes over some 24 orders of magnitude! These challenges are central to the research of the York computational magnetism group.
Applications in magnetic recording
Magnetic materials are everywhere! Our work relates to magnetic recording.
A hard drive contains:
- Magnetic recording medium.
- Magnetic read and write transducers.
- Motors for disc rotation and head movement also contain high performance magnets.
- More information storage in the home.
- Hard drives in mobile phones.
- Biomedical applications (e.g. drug targeting and delivery).
- Long term - Spin electronics. Enhances electronics using the spin of the electron rather than merely the charge.
Our Research
We are developing new computational and theoretical approaches to the study of magnetic materials, recognising the physical and technical challenges of nanomagnetism. The aim is to link quantum ideas arising from density functional theory with a statistical mechanical formalism capable of describing phase transitions.
Some of our current projects:
- Investigations of laser heating of magnetic materials in the sub-picosecond regime.
- Development of the theoretical basis of multiscale models linking ab-initio, atomistic and micromagnetic lengthscales.
- Exchange bias - an important phenomenon arising in coupled ferro- and antiferro- magnetic materials.
- Models of the structure of magnetic nanoparticles and the effect of morphology and surfaces on magnetic properties.
- Theory of "spin torque" - the interaction between polarised electrons and magnetism. Important for the development of spin electronics.
- "Opto-magnetism" - the exciting recent discovery of the ability to reverse the magnetisation on the sub-picosecond timescale using circularly polarised laser light.