A single crystal high-temperature pyrochlore antiferromagnet

Abstract

We report the magnetic characterization of the frustrated transition metal pyrochlore NaCaCo${}_2$F${}_7$. This material has high spin Co${}^{2+}$ in CoF${}_6$ octahedra in a pyrochlore lattice, and disordered non-magnetic Na and Ca on the large-atom sites in the structure. Large crystals grown by the floating zone method were studied. The magnetic susceptibility is isotropic, the Co moment is larger than the spin-only value, and in spite of the large Curie Weiss theta (-140 K), freezing of the spin system, as characterized by peaks in the ac and dc susceptibility and specific heat, does not occur until around 2.4 K. This yields a frustration index of f = $-{\theta }_{CW}$/$T_f$ $\approx$ 56, an indication that the system is highly frustrated. The observed entropy loss at the freezing transition is low, indicating that magnetic entropy remains present in the system at 0.6 K. The compound may be the realization of a frustrated pyrochlore antiferromagnet with weak bond disorder. The high magnetic interaction strength, strong frustration, and the availability of large single crystals makes NaCaCo${}_2$F${}_7$ an interesting alternative to rare earth oxide pyrochlores for the study of geometric magnetic frustration in pyrochlore lattices.

Submitted to PRL; 14 pages, 4 figures, 2 tables

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• Magnetic Pyrochlore Oxides
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Cited by in corpus (21)

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• Single-ion properties of the $S_{eff}$ = 1/2 XY antiferromagnetic pyrochlores, Na$A^{\prime }$Co${}_2$F${}_7$ ($A^{\prime }=$ Ca${}^{2+}$, Sr${}^{2+}$)
• Static and dynamic XY-like short-range order in a frustrated magnet with exchange disorder
• NaSrMn2F7, NaCaFe2F7, and NaSrFe2F7: novel single crystal pyrochlore antiferromagnets
• Frustrated Magnetism in Fluoride and Chalcogenide Pyrochlore Lattice Materials
• Competing phases and topological excitations of spin-one pyrochlore antiferromagnets
• Spin freezing in the disordered pyrochlore magnet NaCaCo${}_2$F${}_7$: NMR studies and Monte-Carlo simulations
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• Real-space investigation of short-range magnetic correlations in fluoride pyrochlores NaCaCo${}_2$F${}_7$ and NaSrCo${}_2$F${}_7$ with magnetic pair distribution function analysis
• Unusual double-peak specific heat and spin freezing in a spin-2 triangular lattice antiferromagnet FeAl${}_2$Se${}_4$
• $\mu$SR study of spin freezing and persistent spin dynamics in NaCaNi${}_2$F${}_7$
• Magnetic interactions and spin dynamics in the bond-disordered pyrochlore fluoride NaCaCo${}_2$F${}_7$
• Structural and spin-glass properties of single crystal $J_{eff}$ = 1/2 pyrochlore antiferromagnet NaCdCo${}_2$F${}_7$ : correlating $T_f$ with magnetic-bond-disorder
• Softening of breathing elastic mode and trigonal elastic mode in disordered pyrochlore magnet NaCaCo${}_2$F${}_7$
• Absence of long-range order in an $XY$ pyrochlore antiferromagnet Er${}_2$AlSbO${}_7$
• Glassy disordered ground states in the frustrated pyrochlore and fluorite antiferromagnets NaCd$M_2$F${}_7$ ($M$ = Ni${}^{2+}$, Mn${}^{2+}$)
• Low-temperature high-frequency dynamic magnetic susceptibility of classical spin-ice Dy${}_2$Ti${}_2$O${}_7$