NaCaCo 2 F 7 : A single-crystal high-temperature pyrochlore antiferromagnet
NaCaCo 2 F 7 : A single-crystal high-temperature pyrochlore antiferromagnet
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DOI：
10.1103/physrevb.89.214401
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发表时间：
2014-05
影响因子：
3.7
通讯作者：
J. Krizan;R. J. Cava
中科院分区：
文献类型：
--
作者：
J. Krizan;R. J. Cava
We report the magnetic characterization of the frustrated transition metal pyrochlore ${\text{NaCaCo}}_{2}{\mathrm{F}}_{7}$. This material has high spin Co${}^{2+}$ in CoF${}_{6}$ octahedra in a pyrochlore lattice and disordered nonmagnetic 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 (\ensuremath{-}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 $f\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}\ensuremath{-}{\ensuremath{\theta}}_{\mathrm{CW}}/{T}_{f}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}56$, 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 ${\text{NaCaCo}}_{2}{\mathrm{F}}_{7}$ an interesting alternative to rare earth oxide pyrochlores for the study of geometric magnetic frustration in pyrochlore lattices.
We report the magnetic characterization of the frustrated transition metal pyrochlore ${\text{NaCaCo}}_{2}{\mathrm{F}}_{7}$. This material has high spin Co${}^{2+}$ in CoF${}_{6}$ octahedra in a pyrochlore lattice and disordered nonmagnetic 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 (\ensuremath{-}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 $f\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}\ensuremath{-}{\ensuremath{\theta}}_{\mathrm{CW}}/{T}_{f}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}56$, 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 ${\text{NaCaCo}}_{2}{\mathrm{F}}_{7}$ an interesting alternative to rare earth oxide pyrochlores for the study of geometric magnetic frustration in pyrochlore lattices.