Kinetically inhibited order in a diamond-lattice antiferromagnet
|Title||Kinetically inhibited order in a diamond-lattice antiferromagnet|
|Publication Type||Journal Article|
|Year of Publication||2011|
|Authors||MacDougall GJ, Gout D, Zarestky JL, Ehlers G, Podlesnyak A, McGuire MA, Mandrus D, Nagler SE|
|Journal Title||Proceedings of the National Academy of Sciences of the United States of America|
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 Neel ordering. Below the temperature T* = 6.5 K, there is a dramatic change in the elastic scattering line-shape 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.