Investigations of the Magnetic Properties in the Pyrochlore Ho₂Ti₂O₇

Pyrochlore compounds such as R₂Ti₂O₇ (where R is Ho or Dy) have an highly degenerate ground state where the R³⁺ moments obey the "ice rules". This provides access to study extraordinary physical phenomena, like the formation of magnetic monopoles. Recent publications evidence monopoles which can be probed using high frequency (adiabatic) susceptibility measurements [1]. We performed ac susceptibility measurements on a single-crystal Ho₂Ti₂O₇ sample at low temperatures down to 30 mK and magnetic fields up to 14 T. Based on isothermal frequency sweeps we were able to determine spin relaxation rates. Both the real and imaginary parts of the temperature-dependent magnetic susceptibility measurements show the spins freezing below 1 K and provide insight into the magnetic-monopole density.