Tuning interactions in the spin-ice materials Dy${}_2$Ge${}_{2-x}$Si${}_x$O${}_7$ by silicon substitution

Abstract

We report that the lattice constant of Dy${}_2$Ge${}_{2-x}$Si${}_x$O${}_7$ ($x=0,0.02,0.08,0.125$) can be systematically reduced by substituting the non-magnetic germanium ion in the cubic pyrochlore oxide with silicon. A multi-anvil high-pressure synthesis was performed up to 16 GPa and 1100 ${}^{\circ }$C to obtain polycrystalline samples in a solid-state reaction. Measurements of magnetization, ac susceptibility, and heat capacity reveal the typical signatures of a spin-ice phase. From the temperature shift of the peaks, observed in the temperature-dependent heat capacity, we deduce an increase of the strength of the exchange interaction. In conclusion, the reduced lattice constant leads to a changed ratio of the competing exchange and dipolar interaction. This puts the new spin-ice compounds closer towards the phase boundary of short-range spin-ice arrangement and antiferromagnetic long-range order consistent with an observed reduction of the monopole energy scale.

6 pages, 6 figures