title: Kinetically inhibited order in a diamond-lattice antiferromagnet.
abstract: Frustrated magnetic systems exhibit highly degenerate ground states and strong fluctuations, often leading to new physics. An intriguing example of current interest is the antiferromagnet on a diamond lattice, realized physically in A-site spinel materials. This is a prototypical system in three dimensions where frustration arises from competing interactions rather than purely geometric constraints, and theory suggests the possibility of unusual magnetic order at low temperature. Here, we present a comprehensive single-crystal neutron scattering study of CoAl(2)O(4), a highly frustrated A-site spinel. We observe strong diffuse scattering that peaks at wavevectors associated with Néel ordering. Below the temperature T(∗) = 6.5 K, there is a dramatic change in the elastic scattering lineshape accompanied by the emergence of well-defined spin-wave excitations. T(∗) had previously been associated with the onset of glassy behavior. Our new results suggest instead that T(∗) signifies a first-order phase transition, but with true long-range order inhibited by the kinetic freezing of domain walls. This scenario might be expected to occur widely in frustrated systems containing first-order phase transitions and is a natural explanation for existing reports of anomalous glassy behavior in other materials.
authors: Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. macdougallgj@ornl.gov
authors: Gregory J
authors: GJ
authors: MacDougall
authors: Delphine
authors: D
authors: Gout
authors: Jerel L
authors: JL
authors: Zarestky
authors: Georg
authors: G
authors: Ehlers
authors: Andrey
authors: A
authors: Podlesnyak
authors: Michael A
authors: MA
authors: McGuire
authors: David
authors: D
authors: Mandrus
authors: Stephen E
authors: SE
authors: Nagler
mesh_terms: D000465:Algorithms; D000537:Aluminum Oxide / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D003460:Crystallization; D005296:Ferrous Compounds / Q000737:chemistry; D007700:Kinetics; D008280:Magnetics; D008903:Minerals / Q000737:chemistry; D008956:Models, Chemical; D009502:Neutrons; D010087:Oxides / Q000737:chemistry*; D044367:Phase Transition; D012542:Scattering, Radiation; D013696:Temperature; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D005296:Ferrous Compounds; D008903:Minerals; D010087:Oxides; D003035:Cobalt; D000537:Aluminum Oxide; C060728:cobalt oxide