Experiments to challenge theorists

Abstract

“Geometrically frustrated” magnets have interested physicists for many years for the intriguing diversity of elec tronic and magnetic phenomena they reveal [I]. A frustrated magnet is one that contains magnetic moments on units whose geometry inhibits the formation of an ordered state Magnetic frustration is most easily pictured for a triangle of magnetic moments (“spins”) connected by antiferromagnetic interactions that cause nearest neighbor moments to prefer an antiparallel “up-down” spin arrangement (see Figure 1). In this situation, any two moments can align antiparallel, but the third spin cannot be positioned such that it is antiparallel to both its neighbors. Frustrated magnets usually consist of macroscopic array of such frustrated units. It was shown in the mid-90's that ferromagnetically interacting bonds with a large easy axis anisotropy are also highly frustrated sys tems [2].