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

TL;DR

This study demonstrates that silicon substitution in Dy$_2$Ge$_{2-x}$Si$_x$O$_7$ systematically reduces the lattice constant, alters magnetic interactions, and influences the spin-ice phase, providing insights into tuning magnetic properties in pyrochlore oxides.

Contribution

It introduces a method to tune magnetic interactions in spin-ice materials via silicon substitution, affecting the balance between exchange and dipolar interactions.

Findings

Lattice constant decreases with silicon substitution.

Exchange interaction strength increases with reduced lattice constant.

The spin-ice phase approaches the boundary of long-range order.

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.