Professor Stephen Blundell

Abstract:

Critical exponents closely matching those of the N=2 chiral universality class have been obtained for the layered magnetic system cobalt glycerolate using muon spin relaxation. This class was originally introduced to represent geometrically frustrated triangular stacked-layer XY magnets with chiral noncollinear spin structures. Since the present magnetic system is a canted XY system without geometrical frustration or chiral degeneracy, the results indicate that the order parameter for canting in this system plays a similar role to the chiral order parameter in the geometrically frustrated systems, strongly suggesting that both types of noncollinear system share the same universality class.

Abstract:

TmAgGe is an antiferromagnet in which the spins are confined to distorted kagome-like planes at low temperatures. We report angle-dependent measurements of the magnetization M in fields of up to 55 T that show that there are two distinct and separate energy scales present in TmAgGe, each responsible for a set of step-like metamagnetic transitions: weak exchange interactions and strong crystalline-electric-field (CEF) interactions. Simulations of M using a three-dimensional, free-energy minimization technique allow us to specify the physical origin of the metamagnetic transitions in low, in-plane fields. We also show that the transitions observed with the field perpendicular to the kagome planes are associated with the CEF-split multiplet of Tm. © 2007 The American Physical Society.