New relaxation processes in diluted Ho2Ti2O7Ho2Ti2O7

We have studied the spin relaxation in diluted spin ice Ho2-xRxTi2O7Ho2-xRxTi2O7(R=LaorY) by means of neutron scattering. Remarkably, doping with nonmagnetic ions does not relieve the geometrical frustration and the dynamics of the freezing is unaltered whilst the cubic unit cell is maintained. When the nonmagnetic substitution starts to distort the lattice, a new relaxation process is revealed. We present new data from several diluted spin ice samples where Arrhenius behaviour observed in the parent compound, Ho2Ti2O7Ho2Ti2O7 is superseded by other processes including a quantum tunnelling process.