Magnetite is, as its name implies, one of the most naturally magnetic materials on earth. Millennia ago, it was what first clued scientists in to magnetism. But magnetite is also something of a mystery. At low temperatures, the rock completely stops all electricity. At last scientists have figured it out why.
Superconductors have a perpetually interesting, and potentially massively lucrative, quality; when their temperature is dropped down to a certain temperature, they have no more electrical resistance. Electricity flows through them uninterrupted, perpetually, without any applied voltage. People have been investigating them since their discovery, pouring money into the quest to discovery their properties and expand their applications. Magnetite, the 'anti-superconductor', has not received the same attention. It had its research uses, once upon a time. It's the most magnetic naturally-occurring mineral, and provided the study material that gave rise to the first concepts of magnetism. It conducts electricity, like most metals. Unlike most metals, though, when the temperature drops below a certain degree, electric flow is choked off.
The flip from conductor to insulator, at minus 150 degrees Celsius, discovered by Evert Verwey in 1939, has puzzled scientists ever since. Recently, though, a team from the University of Edinburgh was able to peer inside a crystal of magnetite by aiming an X-ray beam at it. The crystal was half the diameter of a human hair. The team dropped the temperature of the crystal, and saw that the entire structure rearranged itself when brought down to negative 150 degrees. The iron atoms, until then happy to let the electrons proceed, suddenly shifted into organized groups of three, pinning the electron between them. The electrons were trapped, and unable to flow, stopping all current through the magnetite.
Understanding the property may help magnetite regain its scientific and engineering significance. Materials that suddenly insulate, switching 'off' at a certain temperature, may be useful, especially if low-temperature superconductor use expands. If not, scientists have still found the answer to a seventy year old mystery involving one of the oldest research materials out there.
Image: Robert Lavinsky