Absence of moment fragmentation in the mixed B -site pyrochlore Nd2GaSbO7

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.

Field-temperature phase diagram of the enigmatic Nd2(Zr1−xTix)2O7

“…In addition, the ordered magnetic moment is larger along the z direction, thus corresponding to a lower θ angle, which indicates that the disorder tends to tilt the pseudospins back toward the local 111 z axes. This picture is consistent with recent observations on Nd-based pyrochlores with a much stronger disorder on the B site [34][35][36], namely, Nd 2 NbScO 7 and Nd 2 GaSbO 7 .…”

“…The level of disorder introduced in the present study on the nonmagnetic site is not strong enough to destabilize thẽ z-AIAO ordering, and on the contrary seems to reinforce it. As previously mentioned, recent studies show that the AIAO state resists to an even stronger disorder [34][35][36]. Consequently, it may be relevant to directly make a substitution on the magnetic site to test the stability of the AIAO state on dilution and to possibly reach the predicted quantum spin liquid ground state when the ratioJz/Jx decreases [12,41].…”

Traversing the pyrochlore stability diagram; microwave-assisted synthesis and discovery of mixed B-site Ln$_2$InSbO$_7$ family

“…However, often these methods are insufficient to produce phase-pure powders. Such is the case for Ln 2 InSbO 7 [80,88], and some select Ln 2 GaSbO 7 compositions [80,82], where impurities persist indefinitely. As an attempt to circumvent the limitation of slow reaction kinetics, we incorporated mechanochemical methods (see Methods § II A), creating extremely fine, homogenous, glassy precursor phases.…”

“…Part of the historical hesitation behind the mixed Bsite pyrochlores comes from the negative connotation of "disorder" and its association with "dirty" samples [81]. Recently, however, there has been a surge of renewed interest in the mixed B-site pyrochlores [82][83][84][85][86][87], driven by the emerging picture of the profound effects that disorder can play on cooperative magnetic properties. Recent experimental studies on Pr 2 Zr 2 O 7 suggest the possibility that disorder may in fact provide a key route in the realization of both exotic, and possibly novel magnetic ground states [55,81].…”

“…Recent experimental studies on Pr 2 Zr 2 O 7 suggest the possibility that disorder may in fact provide a key route in the realization of both exotic, and possibly novel magnetic ground states [55,81]. The studies that do exist for mixed B-site pyrochlores are fascinating in their own right, and the most thorough investigations have indicated that the mixed Ga 3+ Sb 5+ compositions are remarkably similar to the Ln 2 Ti 2 O 7 titanates in both structure and properties [80,[82][83][84]. As such, we postulate that the richness of the Ln 2 B 2 O 7 phases may be mirrored in their mixed B-site counterparts, but with additional chemical degrees of freedom.…”