When Exposed to Air, New Nanomaterial Becomes Magnetic at High Temperatures

Researchers at the University of Washington (UW) have created two new magnetic materials made of silver, chromium and selenium ions, one of which transforms into the other simply by being exposed to air — and the transformation dramatically boosts how hot the material can get while remaining magnetic.

Both materials belong to a family of crystal structures called spinels, in which atoms sit in a repeated lattice built from three types of atomic sites, generically labelled A, B and X. The UW team's spinels are among the first to place a silver ion in the "A" site, the position that determines how the material responds to stimuli such as light, heat or air, the researchers report in the Journal of the American Chemical Society.

When the original silver-containing spinel is exposed to air, it loses silver ions and converts into a second spinel structure. The original material loses its magnetism at 152 Kelvin, or minus 185 degrees Fahrenheit, but the second, air-exposed spinel stays magnetic up to 400 Kelvin, or 260 degrees Fahrenheit — the largest change ever documented in what scientists call the Curie temperature, the highest temperature at which a material remains magnetic.

The researchers say they plan to keep studying both materials to learn more about the fundamentals of magnetism. The findings, led by Ezra K. Bacon-Gershman, are published in the Journal of the American Chemical Society.