Azar Eyvazov
Department of Physics, Cornell University
“Magnetic Glass-Forming Liquid Characteristics in Pyrochlore Titanates Ho2Ti2O7 and Dy2Ti2O7”
Abstract :
In pyrochlore structure the rare-earth ions with large magnetic moments are situated at the corners of the corner sharing tetrahedral network of spins. Due to strong crystal field interactions, at low temperatures the spins in Dysprosium Titanate and Holmium Titanate are forced to point toward the center of one of the tetrahedra that share it. The dipolar interaction between the magnetic moments is comparable to the nearest neighbor ferromagnetic exchange and the combined interaction leads to a low energy state where for each tetrahedron two spins point toward the center and two point away from the center. The spin configuration can be mapped to the proton disorder in the hexagonal ice and low temperature entropy in agreement with Pauling result for hexagonal ice was reported. Very long wait times are necessary to let the spin system relax at low temperatures, indicating slow magnetic dynamics because of the magnetic frustration. To explore the actual magnetic phase formed by cooling these materials, we measure their magnetization dynamics using toroidal, boundary-free magnetization transport techniques. We find the same distinctive phenomenology by the magnetic susceptibility in both compounds that is indistinguishable in form, from that of the dielectric permittivity of dipolar glass-forming liquids. Moreover, Ho2Ti2O7 and Dy2Ti2O7 both exhibit microscopic magnetic relaxation times that increase along the super-Arrhenius trajectories comparable to those observed in glass-forming dipolar liquids. Thus, upon cooling below about 2K, Dy2Ti2O7 and Ho2Ti2O7 both appear to enter the same state with characteristics of a glass-forming spin-liquid. The differences between the glass forming liquid characteristics in two materials can be understood in terms of their known magnetic properties.