Ohio researchers make MRI breakthrough

As well as biomedical imaging, the development is said to hold promise in data storage applications.

Chris Hammel, Ohio Eminent Scholar in Experimental Physics, and his colleagues took a magnetic disk measuring two micrometres wide and 40 nanometres thick and were able to obtain magnetic resonance images of its interior.

The resulting image – with each ‘pixel’ one-tenth the size of the disk itself – is claimed to be the highest-resolution image ever taken of the magnetic fields and interactions inside of a magnet.

Studying the material’s behaviour at these scales is key to incorporating them into computer chips and other electronic devices.

In 2008, Hammel’s team debuted a new kind of high-resolution scanning system that combines MRI, ferromagnetic resonance and atomic force microscopy.

Ferromagnets were used in this study. Because ferromagnets retain a particular polarisation once magnetised, they are already essential components in computers and other electronics, where they provide data storage alongside computer chips. Smaller magnets built directly into a computer chip could do even more, Hammel said.

‘We know that shrinking these magnets to the nanoscale and building them directly inside electronics would enable these devices to do more, and with less power consumption,’ he added. ‘But a key barrier has always been the difficulty of imaging and characterising nanomagnets.’

Typical MRI machines work by inducing a magnetic field inside non-magnetic objects, such as the body. Since ferromagnets are already magnetic, conventional MRI can’t see inside them.

The combination technique that the Ohio State researchers invented is called ‘scanned probe ferromagnetic resonance imaging,’ or scanned probe FMRI, and it involves detecting a magnetic signal using a miniscule silicon bar with a magnetic probe on its tip.

The Ohio team imaged the inside of the magnetic disk 0.2 micrometres at a time. They used a thin film of a commercially available nickel-iron magnetic alloy called Permalloy for the disk.

‘In essence, we were able to conduct ferromagnetic resonance measurements on a small fraction of the disk, then move our probe over a little bit and do magnetic resonance there, and so on,’ said Denis Pelekhov, director of the ENCOMM NanoSystems Laboratory at Ohio State. ’Using these results, we could see how the magnetic properties vary inside the disk.’

Experts suspect that computer chips equipped with tiny magnets might one day provide high-density data storage. Computers with magnets in their central processing units (CPUs) would never have to boot up. The entire computer would be contained inside the CPU, making such devices smaller and less power hungry.

Hammel believes that the technique could one day be a useful tool in biomedical research labs. Researchers could use it to study tissue samples of the plaques that form in brain tissues and arteries, and perhaps develop better ways of detecting them in the body. Knowing how these plaques form could advance studies of many diseases, including Alzheimer’s and atherosclerosis.

The researchers report their findings in the 12 August issue of the journal Nature.