Abstract
In this paper we report on a study, using neutron scattering techniques, of the spin fluctuations in the random magnetic-nonmagnetic antiferromagnets, and , with close to the percolation concentration . The results for are consistent with the multicritical point picture for the percolation point with the temperature scale determined by the inverse correlation length of the appropriate linear chain. This approach gives a very satisfactory account of the spin-space crossover from Heisenberg-like to Ising-like behavior observed in tetragonal . The exponent describing the temperature dependence of the inverse correlation length is found to be 0.85 ± 0.10 for this system and, with rather less certainty, we infer for the cubic . The results for show two unexpected features. Firstly the diffuse scattering does not show any critical scattering associated with the onset of long-range order. We suggest this may be because only a small fraction of spins are in the backbone of the infinite cluster. Secondly in the long-range order decreases on cooling below 6 K. We suggest that this may result from the random magnetic dipole-dipole forces producing a type of spin-glass phase.
- Received 7 May 1980
DOI:https://doi.org/10.1103/PhysRevB.22.4412
©1980 American Physical Society