Geometrically frustrated antiferromagnets

In many materials, Coulomb interactions between electrons lead to an insulating state, in which the erstwhile conduction electrons now become localized on individual orbitals. Their spin degree of freedom leads to local moments, which interact via antiferromagnetic exchange interactions. If the geometry of the crystal lattice causes the leading exchange interactions to compete, the result is often a macroscopic degeneracy of minimum energy configurations at the classical level. The low temperature physics of such systems is then controlled by the interplay of quantum and thermal fluctuations and subdominant interactions. In this talk, I will first review this physics, and then describe one specific class of magnets, triangular lattice Ising antiferromagnets in a transverse field, focusing on an interesting prediction of a low-field divergence in the intermediate-temperature **ferromagnetic** susceptibility of such **antiferromagnets**.