Absence of moment fragmentation in the mixed $B$-site pyrochlore Nd$_{2}$GaSbO$_{7}$

TL;DR

This study investigates the absence of moment fragmentation in the Nd-based pyrochlore Nd$_{2}$GaSbO$_{7}$, revealing that chemical pressure influences this phenomenon more than B-site disorder, which does not induce spin glass behavior.

Contribution

The paper demonstrates that in Nd pyrochlores, chemical pressure rather than B-site disorder determines the presence of moment fragmentation, challenging previous assumptions.

Findings

No evidence of moment fragmentation in Nd$_{2}$GaSbO$_{7}$

B-site disorder does not induce spin glass state

All-in-all-out magnetic order persists

Abstract

Nd-based pyrochlore oxides of the form Nd$_{2}B_{2}$O$_{7}$ have garnered a significant amount of interest owing to the moment fragmentation physics observed in Nd$_{2}$Zr$_{2}$O$_{7}$ and speculated in Nd$_{2}$Hf$_{2}$O$_{7}$. Notably this phenomenon is not ubiquitous in this family, as it is absent in Nd$_{2}$Sn$_{2}$O$_{7}$, which features a smaller ionic radius on the $B$-site. Here, we explore the necessary conditions for moment fragmentation in the Nd pyrochlore family through a detailed study of the mixed $B$-site pyrochlore Nd$_{2}$GaSbO$_{7}$. The $B$-site of this system is characterized by significant disorder and an extremely small average ionic radius. Similarly to Nd$_{2}$Sn$_{2}$O$_{7}$, we find no evidence for moment fragmentation through our bulk characterization and neutron scattering experiments, indicating that chemical pressure (and not necessarily the $B$-site disorder) plays a key role in the presence or absence of this phenomenon in this material family. Surprisingly, the presence of significant $B$-site disorder in Nd$_{2}$GaSbO$_{7}$ does not generate a spin glass ground state and instead the same all-in-all-out magnetic order identified in other Nd pyrochlores is found here.