NaSrCo₂F₇, a Co²⁺ pyrochlore antiferromagnet

We report the crystal growth, by the Bridgeman-Stockbarger method, and the basic magnetic properties of a new cobalt-based pyrochlore, NaSrCo₂F₇. Single-crystal structure determination shows that Na and Sr are completely disordered on the non-magnetic large atom A sites, while magnetic Co²⁺ fully occupies the pyrochlore lattice B sites. NaSrCo₂F₇ displays strong antiferromagnetic interactions (), a large effective moment (), and no spin freezing until 3 K. Thus, NaSrCo₂F₇ is a geometrically frustrated antiferromagnet with a frustration index . Ac susceptibility, dc susceptibility, and heat capacity are utilized to characterize the spin freezing. We argue that NaSrCo₂F₇ and the related material NaCaCo₂F₇ are examples of frustrated pyrochlore antiferromagnets with weak bond disorder.