Field Induced Order and Spin Waves in the Pyrochlore Antiferromagnet Tb 2 Ti 2 O 7

1. Field Induced Order and Spin Waves in the Pyrochlore Antiferromagnet Tb2Ti2O7 K.C. Rule1, J.P.C. Ruff1, B.D. Gaulin1, S.R. Dunsiger1, J.P. Clancy1, M.J. Lewis1, H.A. Dabkowska1, I. Mirebeau2, P. Manuel3, J.S. Gardner4, Y. Qiu4,5, and J.R.D. Copley4 1McMaster U. (Canada), 2CEA Saclay (France), 3ISIS (UK), 4CHRNS, 5U. Maryland DMR-0454672 Tb2Ti2O7 is a geometrically frustrated antiferromagnet in which magnetic Tb3+ ions are located at the vertices of a network of corner-sharing tetrahedra. High resolution time-of-flight experiments using the CHRNS DCS with long wavelength (5 Å and 9 Å) neutrons, in “fields” as high as 9 T, reveal a complex magnetic-field vs temperature phase diagram; a cooperative paramagnet, a polarized paramagnet, and a high field long range ordered phase. Panels a, b and c show the measured diffuse intensity at 1K, integrated over low energies (-0.5 to 0.5 meV); panel d shows the elastic and near-elastic scattering integrated over Q, including the (002) position. As the field is increased additional Bragg peaks appear and the diffuse scattering around (002) disappears. Other measurements, at 0.4 K, show that in the ordered phase (above ~2 T) there are well-defined spin-wave excitations. These new observations of complex behavior in Tb2Ti2O7 will hopefully motivate theoretical study aimed at a more complete understanding of this enigmatic material. K.C. Rule, J.P.C. Ruff, B.D. Gaulin, S.R. Dunsiger, J.S. Gardner, J.P. Clancy, M.J. Lewis, H.A. Dabkowska, I. Mirebeau, P. Manuel, Y. Qiu, and J.R.D.Copley, Phys. Rev. Lett. 96, 177201 (2006).