NEUTRON-SCATTERING STUDY OF THE 2-DIMENSIONAL FRUSTRATED ANTIFERROMAGNET RB2CU0.12CO0.88F4

Quasielastic neutron scattering is performed on a single crystal of th e two-dimensional antiferromagnet Rb2Cu0.12Co0.88F4, whose magnetic st ructure is frustrated by the admixture of ferromagnetic bonds. From th e critical scattering, the in-plane inverse correlation length is foun d to decrease linearly with the temperature, with a critical exponent nu = 1.02 +/- 0.04. At the onset of the sublattice magnetization, whic h occurs at T(N) = 88.1 +/- 0.1 K, however, the in-plane correlations have not yet become long ranged. At T(N), the planar domain size has g rown to only 14 lattice spacings. Below T(N), the planar domains size increases further, to attain length scales beyond resolution at about 75 K. Conversely, the domains break up into smaller ones in this tempe rature range upon warming up. For the critical exponent of the suscept ibility we find gamma = 1.5 +/- 0.2 after correction for the finite co rrelation remaining at T(N). The sublattice magnetization obeys the cr itical exponent beta = 0.16 +/- 0.04. The critical exponents found com pare with the Ising values nu = 1, gamma = 7/4, and beta = 1/8. Anothe r manifestation of the frustration is the failure to reach true equili brium below T(N). This is reflected in a dependence of the c-axis corr elations on the cooling rate, and in a small increment of the intralay er and in-layer correlation lengths over long times.