Tb₂Ti₂O₇: a ‘spin liquid’ single crystal studied under high pressure and high magnetic field

Abstract

Tb2Ti2O7 is a very intriguing case of a geometrically frustrated compound where the short range correlated moments still fluctuate down to extremely low temperatures. We studied this compound by means of single-crystal neutron diffraction for an unprecedented range of thermodynamical parameters combining high pressures (up to 2.8 GPa), high magnetic fields (up to 7 T) and low temperatures (down to 0.14 K). We also investigated the effects of several conditions: a hydrostatic pressure, a uniaxial stress and a combination of the two. We show that a long range antiferromagnetic phase can be induced under pressure. The Néel temperature and the ordered magnetic moment may be tuned by means of the direction of the anisotropic pressure component. Under an applied field, the antiferromagnetic structure transforms into a non-collinear ferromagnetic one at a low field of 0.3 T; then the spin canting persists up to very high fields (above 7 T). Thermal and field hysteresis phenomena are observed at low fields and low temperatures. We show the pressure and magnetic field magnetic phase diagram deduced from our data. We also present microscopic models for the neutron correlations deduced from a refinement of the neutron intensities, using both symmetry analysis and simulated annealing processes. We discuss the implications of these results for the understanding of the mysterious spin liquid phase stabilized at ambient pressure.