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.

11 pages, 8 figures