Non-magnetic materials combine into megagauss sensors

A University of Chicago led research team has reported combining non-magnetic materials into megagauss sensors, the most sensitive magnetic sensors developed for extremely large fields.

A research team led by physicists at the University of Chicago have reported in the journal Nature that they have combined non-magnetic materials into megagauss sensors, the most sensitive magnetic sensors ever developed for extremely large fields.

The sensors’ potential applications range from medical imaging to better understanding the physics of high-temperature superconductivity.

The researchers have used silver chalcogenides to make extremely precise measurements of magnetic fields as high as 600,000 Gauss, or more than a million times the Earth’s magnetic field, at the National High Magnetic Field Laboratory at Los Alamos National Laboratory.

Conventional techniques are said to have difficulty measuring magnetic fields more than approximately 250,000 Gauss, and they do so with less accuracy.

In the medical arena, the megagauss sensors would serve as a more sensitive detector for high-field Magnetic Resonance Imaging applications.

‘If you need to know the magnetic field very accurately, and if the field changes a lot over a small region of space, then these sensors would be very good,’ said Thomas Rosenbaum, the James Franck Professor in Physics at the University of Chicago.

The sensors also could be useful for studying the physics that underlies high-temperature superconductors, which have been touted for potential applications ranging from superfast computers to levitating trains.

‘One way to do that is to apply a magnetic field that kills the superconductivity and ask, what’s left? What does that so-called normal state look like? The magnetic fields you need for that are huge,’ Rosenbaum said. ‘These large magnetic fields let you get at physics that you otherwise just can’t get at.’

The study was led by Anke Husmann, formerly a postdoctoral researcher at the University of Chicago, now with Toshiba Research Laboratory in Cambridge, England.

‘The drive to obtain the highest possible magnetic fields cuts across disciplinary boundaries, but it has particularly potent implications for materials science,’ wrote Husmann and her colleagues in their Nature article. That’s because magnetic fields change the way electrons move through solids. ‘The nature of these changes reveals information about the electronic structure of a material and, in auspicious circumstances, can be harnessed for applications,’ they wrote.

The research team knew from previous experiments that silver chalcogenides — which consist of two parts silver, one part selenium and one part tellurium — showed no response to magnetic field.

‘But if you went with a tiny bit extra silver, say one part in 10,000, or a little more tellurium or selenium, all of a sudden the material was incredibly sensitive to magnetic field,’ Rosenbaum said.

The team had originally planned to study silver chalcogenides to see if they could probe the structure of glassy materials by looking at the movement of electrical charge. But when they applied a magnetic field to the material, they observed an unexpectedly large response.

Rosenbaum noted that the sensors are small, cheap and sensitive. The sensors measure approximately one cubic millimetre, about the size of a pencil tip. The materials cost only pennies in those quantities, and they are said to be capable of measuring extremely large magnetic fields with an accuracy of a fraction of a percent.