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

References in corpus (4)

• Low Temperature Spin Freezing in Dy2Ti2O7 Spin Ice
• Spin Freezing in Geometrically Frustrated Antiferromagnets with Weak Disorder
• Spin-glass transition in bond-disordered Heisenberg antiferromagnets coupled with local lattice distortions on a pyrochlore lattice
• Kagome-Triangular Lattice Antiferromagnet NaBa2Mn3F11