Physicists at Ohio State University have developed a new kind of MRI technique that allows scientists to see inside a ferromagnet that’s smaller than the head of a pin.

Chris Hammel, Ohio Eminent Scholar in Experimental Physics at Ohio State University, explained: “The magnets we study are basically the same as a refrigerator magnet, only much smaller.”

The disk-shaped magnets used in this study measure just two micrometers in diameter.

Hammel continued: “Because ferromagnets generate such strong magnetic fields, we can’t study them with typical MRI. A related technique, ferromagnetic resonance, or FMR, would work, but its net sensitive enough to study individual magnets that are this small.”

The new technique combines three different kinds of technology: MRI, FMR, and atomic force microscopy. Dubbed ‘scanned probe ferromagnetic resonance force microscopy’, or scanned probe FMRFM, it involves detecting a magnetic signal using a tiny silicon bar with an even tinier magnetic probe on its tip.

As the probe passes over a material, it captures a bowl-shape imaged: a curved cross-section of an object. The magnetic signal is more intense in the middle (the ‘bottom’ of the bowl), and fades towards the edges – this is why the new technique works.

Every atom emits radio waves at a particular frequency, but to know where those atoms are, scientists need to be able to localise where the radio waves are coming from.

Large-scale MRI machines, such as those in hospitals, get around this problem by varying the magnetic field by precise amounts as it sweeps over an object. The computer controlling the MRI knows that where the magnetic field equals X, the location equals Y. Sophisitcated software combines the data, and doctors get a 3D view inside a patient’s body.

For Hammel’s tiny magnets, no methods were previously known that would image the inside of them, much less allow for precise localisation. But since the new probe system generates a magnetic field that varies naturally, the physicists discovered that they could sweep the probe over an array of magnets and get a 2D view that is similar to a medical MRI.

Experts believe that one day, tiny magnets could be implanted on a computer’s central processing unit (CPU) chip. Because system data could be recorded on the magnets, such a computer would never need to boot up. It would be very small; essentially the entire computer would be contained in the CPU.

The technique could also be used for biomedical research. Many diseases are associated with plaques that form in brain tissues and in arteries in the body. Many diseases are associated with plaques, including Alzheimer’s and atherosclerosis. Currently, researchers are trying to study the structure of plaques in detail to understand how they form and how they affect conventional MRI images.