Classical Antiferromagnet on a Hyperkagome Lattice

Motivated by recent experiments on Na4Ir3O8 [Y. Okamoto, M. Nohara, H. Aruga-Katori, and H. Takagi, arXiv:0705.2821 (unpublished)], we study the classical antiferromagnet on a frustrated three-dimensional lattice obtained by selectively removing one of four sites in each tetrahedron of the pyrochlore lattice. This “hyperkagome” lattice consists of corner-sharing triangles. We present the results of large-N mean field theory and Monte Carlo computations on ON classical spin models. It is found that the classical ground states are highly degenerate. Nonetheless a nematic order emerges at low temperatures in the Heisenberg model (N = 3) via “order by disorder,” representing the dominance of coplanar spin configurations. Implications for ongoing experiments are discussed.

John M. Hopkinson,1 Sergei V. Isakov,1 Hae-Young Kee,1 and Yong Baek Kim1,2
1Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada
2Department of Physics, University of California, Berkeley, California 94720, USA