K. C. Rule

Structural Fluctuations in the spin-liquid state of Tb2Ti2O7.

High-resolution x-ray scattering measurements on single crystal Tb2Ti2O7 reveal finite structural correlations at low temperatures. This geometrically frustrated pyrochlore is known to exhibit a spin-liquid or cooperative paramagnetic state at temperatures below approximately 20 K. Parametric studies of structural Bragg peaks appropriate to the Fd3[over ]m space group of Tb2Ti2O7 reveal substantial broadening and peak intensity reduction in the temperature regime 20 K to 300 mK. We also observe a small, anomalous lattice expansion on cooling below a density maximum at approximately 18 K. These measurements are consistent with the development of fluctuations above a cooperative Jahn-Teller, cubic-tetragonal phase transition at very low temperatures.

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

High resolution time-of-flight neutron scattering measurements on Tb(2)Ti(2)0(7) reveal a rich low temperature phase diagram in the presence of a magnetic field applied along [110]. In zero field at T = 0.4 K, Tb(2)Ti(2)0(7) is a highly correlated cooperative paramagnet with disordered spins residing on a pyrochlore lattice of corner-sharing tetrahedra. Application of a small field condenses much of the magnetic diffuse scattering, characteristic of the disordered spins, into a new Bragg peak characteristic of a polarized paramagnet. At higher fields, a magnetically ordered phase is induced, which supports spin wave excitations indicative of continuous, rather than Ising-like, spin degrees of freedom.

Magnetic Soft Modes in the Distorted Triangular Antiferromagnet α-CaCr2O4

In this Letter, we explore the phase diagram and excitations of a distorted triangular lattice antiferromagnet. The unique two-dimensional distortion considered here is very different from the isosceles-type distortion that has been extensively investigated. We show that it is able to stabilize a 120° spin structure for a large range of exchange interaction values, while new structures are found for extreme distortions. A physical realization of this model is α-CaCr(2)O(4), which has a 120° structure but lies very close to the phase boundary. This is verified by inelastic neutron scattering which reveals unusual rotonlike minima at reciprocal space points different from those corresponding to the magnetic order.

Instability of magnons in two-dimensional antiferromagnets at high magnetic fields

Spin dynamics of the square lattice Heisenberg antiferromagnet,

Magnetic excitations of the gapped quantum spin dimer antiferromagnet Sr 3 Cr 2 O 8

{text{Ba}}_{2}{text{MnGe}}_{2}{text{O}}_{7}

Magnetic and crystal structure of azurite Cu3(CO3)2(OH)2as determined by neutron diffraction

, is studied by a combination of bulk measurements, neutron diffraction, and inelastic neutron-scattering techniques. Easy plane type antiferromagnetic order is identified at

The dynamics of azurite Cu3(CO3)2(OH)2 in a magnetic field as determined by neutron scattering

Tensuremath{le}4.0text{ }text{K}

Asymmetric thermal line shape broadening in a gapped 3D antiferromagnet: evidence for strong correlations at finite temperature.

. The exchange interactions are estimated as

Magnetoelastic and structural properties of azurite Cu 3 ( CO 3 ) 2 ( OH ) 2 from neutron scattering and muon spin rotation

{J}_{1}=27.8(3)text{ }ensuremath{mu}text{eV}

Neutron scattering investigations of the partially ordered pyrochlore Tb2Sn2O7

and