NaCaCo 2 F 7 : A single-crystal high-temperature pyrochlore antiferromagnet

摘要: We report the magnetic characterization of frustrated transition metal pyrochlore ${\text{NaCaCo}}_{2}{\mathrm{F}}_{7}$. This material has high spin Co${}^{2+}$ in CoF${}_{6}$ octahedra a lattice and disordered nonmagnetic Na Ca on large-atom sites structure. Large crystals grown by floating zone method were studied. The susceptibility is isotropic; Co moment larger than spin-only value; spite large Curie Weiss theta (\ensuremath{-}140 K), freezing system, as characterized peaks ac dc specific heat, does not occur until around 2.4 K. yields frustration index $f\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}\ensuremath{-}{\ensuremath{\theta}}_{\mathrm{CW}}/{T}_{f}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}56$, an indication that system highly frustrated. observed entropy loss at low, indicating remains present 0.6 compound may be realization antiferromagnet with weak bond disorder. interaction strength, strong frustration, availability single makes ${\text{NaCaCo}}_{2}{\mathrm{F}}_{7}$ interesting alternative to rare earth oxide pyrochlores for study geometric lattices.