${\mathrm{Er}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ has been suggested to be a realization of the frustrated $〈111〉\mathrm{XY}$ pyrochlore lattice antiferromagnet, for which theory predicts fluctuation-induced symmetry breaking in a highly degenerate ground state manifold. We present a theoretical analysis of the classical model compared to neutron scattering experiments on the real material, both below and above $T_N=1.173\mathrm{}\left(2\right)\mathrm{}\mathrm{K}.$ The model correctly predicts the ordered magnetic structure, suggesting that the real system has order stabilized by zero-point quantum fluctuations that can be modeled by classical spin wave theory. However, the model fails to describe the excitations of the system, which show unusual features.

Results of ac-susceptibility, specific-heat, magnetization, and electron-spin-resonance studies of a $\left[{\text{Gd}}_2{\left(\text{fum}\right)}_3{\left({\text{H}}_2\text{O}\right)}_4\right]\cdot 3{\text{H}}_2\text{O}$ ($\text{fum}=\text{fumarate}$, ${\text{C}}_4{\text{H}}_2{\text{O}}_4$) powder samples are reported. The results of these measurements enabled us to identify the studied compound as a three-dimensional $S=7/2$ Heisenberg magnet with $T_N=0.19\text{K}$ and dominant crystal-field anisotropy. The susceptibility studies conducted at audio frequencies and temperatures from 2 to 30 K revealed that the application of static magnetic fields induces a slow spin relaxation. The relaxation is not associated with an anisotropy energy barrier and is explicable assuming resonant phonon trapping. The magnetic field dependence of the relaxation time is consistent with the proposed scenario and suggests that a strong spin-lattice interaction may be the mechanism governing the relaxation properties in the studied system.

Magnetocaloric properties of ${\text{KEr}\left({\mathrm{MoO}}_4\right)}_2$ single crystals were investigated using magnetization and specific heat measurements in the magnetic field applied along the easy and hard axis. Large conventional magnetocaloric effect was found around 10 K ($-\mathrm{\Delta }{S}_{\max }=14$ J/kg K for 5 T) in the field applied along the easy axis. What is more, a huge magnetic anisotropy in the $ab$ plane leads to a large anisotropy of magnetocaloric effect, $-\mathrm{\Delta }{S}_{\mathrm{R},\max }=10$ and 13 J/kg K obtained by a simple rotating of the single crystal within the $ab$ plane in the constant magnetic field 2 and 5 T, respectively. Large $\mathrm{\Delta }{S}_{\mathrm{R}}$ values with no hysteresis losses and rather wide working temperature spans imply that ${\text{KEr}\left({\mathrm{MoO}}_4\right)}_2$ may serve as a promising candidate for the implementation of a compact rotary magnetic cryorefrigerator.

The magnetocaloric effect of polycrystalline samples of pure and Y-doped dipolar spin ice ${\mathrm{Dy}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ was investigated at temperatures from nominally $0.3\text{to}6\mathrm{K}$ and in magnetic fields of up to $2\mathrm{T}$. As well as being of intrinsic interest, it is proposed that the magnetocaloric effect may be used as an appropriate tool for the qualitative study of slow relaxation processes in the spin ice regime. In the high-temperature regime the temperature change on adiabatic demagnetization was found to be consistent with previously published entropy vs temperature curves. At low temperatures $(T<0.4\mathrm{K})$ cooling by adiabatic demagnetization was followed by an irreversible rise in temperature that persisted after the removal of the applied field. The relaxation time derived from this temperature rise was found to increase rapidly down to $0.3\mathrm{K}$. The data near $0.3\mathrm{K}$ indicated a transition into a metastable state with much slower relaxation, supporting recent neutron-scattering results. In addition, magnetic dilution of 50% concentration was found to significantly prolong the dynamical response in the mK temperature range, in contrast with results reported for higher temperatures at which the spin correlations are suppressed. These observations are discussed in terms of defects and loop correlations in the spin ice state.