  We report low-temperature susceptibility and magnetisation data for the cubic
pyrochlore Er2Ti2O7. By performing the measurements on single crystals we are
able to establish the degree of magnetic anisotropy present in this compound
and to determine the critical values for magnetic field induced transitions
below the magnetic ordering temperature of 1.2 K. We also present a magnetic
H-T phase diagram of this quantum XY antiferromagnet for different directions
of an applied field.

Strongly Correlated Electrons