How can 2 Metals that are Non-Magnetic Combine to make a Magnet?

Rice University researchers (from left) Emilia Morosan, Eteri Svanidze and Jiakui Wang revealed their discovery of the first itinerant antiferromagnet. Credit: Jeff Fitlow/Rice University

Combining Titanium and Gold to make 1st itinerant antiferromagnet: TiAu. This is not the kind of magnet one would stick to a refrigerator. Magnetic order only appears in TiAu when the metal is cooled to 36K = -395F. “Magnetization is a function of temperature,” said lead author Eteri Svanidze. “The magnet’s ordering temperature appears as an anomaly in the smooth curve we see in such magnetization measurements.” For common magnets, it is generally 100s of degs F, way hotter than any kitchen. But the energy and temperature scale in unconventional magnets, like the few that have no magnetic elements, are drastically reduced.

Magnets will enhance studies of other important physics, like phase ransitions (as in solid-to-liquid or liquid-to-gas) that take place at absolute zero, called quantum phase transitions. TiAu is only the 3rd known itinerant magnetic metal made with no magnetic elements. The other 2, both ferromagnets that activate their magnetic order at temperatures even colder than TiAu, were discovered half a century ago. Part of the reason for the long gap is that TiAu is challenging to make.

Materials usually become magnetic when exposed to a field that brings the magnetic moments of its atoms into alignment. The magnetic moment of a material can be local (tied to a specific atom) or itinerant (not bonded to a single atom). Itinerant wanderers can extend their influence over more than one atom, facilitating communications between their “up” or “down” spin states. They also allow for handy things like electrical conductivity in metals.

Temperature-dependent magnetization of TiAu.

Atomic moments in local-moment ferromagnets ie common magnetic materials – align all of their spins in the same direction. In an antiferromagnet, the atomic moments align in opposite directions.

“Theoretically we understand local-moment magnetism quite well, and we have some understanding of the itinerant moment, but most true systems really live in between,” she said. “We have to understand the extremes in order to figure out the physics of what’s going on in between.”
“This is the first time such an antiferromagnetic material has been discovered, so it is fundamentally significant. It makes our understanding of magnetism deeper.” http://news.rice.edu/2015/07/14/nonmagnetic-duo-form-unique-magnet/