Spin liquid and spin ice under high pressure: a neutron study ofR2Ti2O7 (R = Tb,Ho)

Abstract

The rare earth titanates show unusual types of short range magnetic order, known as spinliquid and spin ice states, which arise from the geometrical frustration of the pyrochlorelattice. We have investigated the effect of applied pressures on these magneticstates by means of powder neutron diffraction, up to 8 GPa. In the spin liquidTb2Ti2O7, pressureinduces a long range antiferromagnetic order, coexisting with the spin liquid state below the Néel temperature(TN = 2.1 K). The onset of long range order coincides with a strong decrease of the diffuse intensity,due to a gradual transfer from the liquid to the ordered state as the temperaturedecreases. The short range correlations are also modified under pressure, even aboveTN. Incontrast, in Ho2Ti2O7 the spin ice state remains stable under pressure, as was checked up to 6 GPa, and down to1.4 K. The short range correlations are unaffected here. The possible origins of thisbehaviour are discussed.