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

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.