Supplying power to the world's strongest long-pulse magnet at Los Alamos' National High Magnetic Field Laboratory is a 1.4 billion-watt generator, itself the largest among magnetic power sources. It can produce enough energy to power the entire state of New Mexico. Photo by Kevin N. Roark, Public Affairs
Using a new and exotic material called Silver 2-Selenium, a metal that exhibits a uniform sensitivity to a variety of magnetic field intensities, coupled with Los Alamos-designed digital signaling hardware and software, scientists have created "MegaGauss Sensors" capable of taking nearly noise-free measurements in extremely high magnetic fields. This new development will be highlighted in today's issue of Nature, the prestigious British scientific journal. The sensors were developed by a team of scientists from the National High Magnetic Field Laboratory, the University of Chicago and Argonne National Laboratory.
The work included Los Alamos researchers Jon Betts, Al Migliori and Greg Boebinger of MST-NHMFL and was led by Anke Husmann, formerly a postdoctoral researcher at the University of Chicago, now with Toshiba Research Laboratory in Cambridge, England.
"In addition to having a striking new phenomenon whose physical origin is not yet understood, we have apparently solved a technological problem associated with measuring transient magnetic fields accurately," said Boebinger.
In a previous Nature paper, physicists from Chicago and Argonne investigated the Silver 2-Selenium, which was discovered to have a linear magnetoresistance. This, in essence, means that the material's resistance varies linearly with the magnetic field. The research in this week's Nature demonstrates that this linear dependence persists to above 50 Tesla (a million times the Earth's magnetic field).
Measurements at these conditions are possible in the pulsed magnets at the NHMFL and show that Silver 2-Selenium's sensitivity to a small magnetic field is the same as its sensitivity to a large magnetic field. This characteristic makes this material an ideal candidate for a magnetic field sensor.
In order to characterize linear magnetoresistance, both the resistance and the Hall voltage, that is the voltage perpendicular to the applied current, often an indication of the number of charge carriers in a material, must be measured. For these measurements, the NHMFL developed digital signal processing hardware and software that would enable researchers to retrieve data that were clean and noise free in a 60 Tesla short pulse magnet - as if taken in a direct current magnetic field.
"As a leading pulsed magnet lab, the NHMFL was a logical place to do this kind of work," said Boebinger. "The NHMFL is equipped with high-field pulsed magnets (50 and 60 Tesla) wherein these type of measurements are easily taken."
Measurement of magnetic fields becomes more and more difficult as the fields increase in strength because of the length of the pulse. As the field increases, the magnet is only able to reach that field during a very short pulse - usually microseconds. Therefore, it is advantageous to use a magnetic field sensor that is sensitive enough to detect the field as quickly as possible, and in extreme conditions, like those found above 50 Tesla.
The article in this week's issue of Nature argues that Silver 2-Selenium is uniquely capable of sensing the magnetic field relatively simply and accurately, better than any other competing technology.
To read a University of Chicago news release, click here.