There has been a long standing fascination in the physics community with placing antiferromagnetically coupled spins on lattices with triangular motifs. The question of the role of the lattice in determining the ground state can be extended to the three dimensions by examining a network of corner sharing tetrahedra. The ground state

of this system is an open theoretical question even for classical spins. On the surface, the system should have a macroscopically degenerate ground state. However, questions remain about the role of quantum fluctuations.

In spinels, with characteristic stoichiometry AB₂O₄, the B sublattice forms a network of corner sharing tetrahedra. The most frustrated spinel, ZnCr₂O₄, undergoes a spin-Peierls-like phase transition at 12.5 K from a gapless cubic spin liquid to a tetragonal Neel state with a local resonance at 4.5 meV. We have performed polarized and unpolarized neutron diffraction measurements on polycrystalline samples and single crystals to determine the magnetic structure of the Neel state.

Our data can be explained by a complex spin structure in which multiple domains with

different characterestic wave vectors vary in fraction from sample to sample. However, the resonance at 4.5 meV is robust against such variations. This suggests that the cubic spin liquid state of ZnCr₂O₄ is in proximity to a critical point in the macroscopically degenerate ground state manifold.

Name : William Ratcliff
Division: 856 
Laboratory: NCNR
Room and Building address: Rm A122, Bldg 235 
Mail Stop:  8562
Telephone  301-975-4316
FAX:  921-9847
email:  ylem@nist.gov
Sigma Xi member?  No

Category: Physics