First order metamagnetic transition in Ho2Ti2O7 observed by vibrating   coil magnetometry at milli-Kelvin temperatures
  We report vibrating coil magnetometry of the spin ice system Ho2Ti2O7 down to ~0.04 K for magnetic fields up to 5 T applied parallel to the [111] axis. History dependent behavior emerges below T*_0 ~ 0.6 K near zero magnetic field, in common with other spin ice compounds. In large magnetic fields we observe a magnetization plateau followed by a hysteretic metamagnetic transition. The temperature dependence of the coercive fields as well as the susceptibility calculated from the magnetization identify the metamagnetic transition as a line of first order transitions terminating in a critical endpoint at T*_m ~ 0.37 K, B*_m ~ 1.5 T. The metamagnetic transition in Ho2Ti2O7 is strongly reminiscent of that observed in Dy2Ti2O7, suggestive of a general feature of the spin ices. 
C. Krey, S. Legl, S. R. Dunsiger, M. Meven, J. S. Gardner, J. M. Roper   and C. Pfleiderer
cond-mat.str-el