NaSrMn2F7, NaCaFe2F7, and NaSrFe2F7: novel single crystal pyrochlore antiferromagnets

TL;DR

This study reports the synthesis and characterization of three new pyrochlore antiferromagnets, revealing their frustrated magnetic behavior and potential for studying geometric magnetic frustration.

Contribution

The paper introduces three novel single crystal pyrochlore compounds with detailed magnetic property analysis, highlighting their weak bond disorder and spin glass behavior.

Findings

High effective magnetic moments and large Curie-Weiss temperatures observed.

Spin freezing occurs only at low temperatures despite strong magnetic interactions.

Materials exhibit characteristics of frustrated pyrochlore antiferromagnets.

Abstract

The crystal structures and magnetic properties of three previously unreported A2B2F7 pyrochlore materials, NaSrMn2F7, NaCaFe2F7, and NaSrFe2F7 are presented. In these compounds, either S=2 Fe2+ or S=5/2 Mn2+ is on the B site, while nonmagnetic Na and Ca (Na and Sr) are disordered on the A site. The materials, which were grown as crystals via the floating zone method, display high effective magnetic moments and large Curie-Weiss thetas. Despite these characteristics, freezing of the magnetic spins, characterized by peaks in the susceptibility or specific heat, is not observed until low temperatures. The empirical frustration index, f=- {\theta}cw/Tf, for the materials are 36 (NaSrMn2F7), 27 (NaSrFe2F7), and 19 (NaCaFe2F7). AC susceptibility, DC susceptibility, and heat capacity measurements are used to characterize the observed spin glass behavior. The results suggest that the compounds are frustrated pyrochlore antiferromagnets with weak bond disorder. The magnetic phenomena that these fluoride pyrochlores exhibit, in addition to their availability as relatively large single crystals, make them promising candidates for the study of geometric magnetic frustration.