Abstract
NMR, muon spin rotation magnetization, and specific-heat measurements in powders and single crystals are reported. Specific-heat and magnetization measurements evidence that is a frustrated two-dimensional Heisenberg antiferromagnet on a square lattice with a superexchange coupling along the sides of the square, almost equal to the one along the diagonal with At a phase transition to a low-temperature collinear order is observed. and the sublattice magnetization, derived from NMR and were found practically independent on the magnetic field intensity up to 9 T. The critical exponent of the sublattice magnetization was estimated β≃0.235, nearly coincident with the one predicted for a two-dimensional system on a finite size. The different magnetic properties found above and below are associated with the modifications in the spin Hamiltonian arising from a structural distortion occurring just above
- Received 19 December 2000
DOI:https://doi.org/10.1103/PhysRevB.64.024409
©2001 American Physical Society