We report on first perturbed angular correlation (PAC) measurements in the 2D triangular antiferromagnet CuFe${\mathrm{O}}_2$. The implanted ${}^{111}$In PAC probes resides on Fe sites and sense the combined hyperfine interaction of the structural electric field gradient and an antiferromagnetic internal field which is surprisingly small as compared to other ferromagnetic or antiferromagnetic oxides. This is explained by a local change in the frustrated triangular lattice leads to a perfect cancellation of the magnetic hyperfine fields of the probe's next-neighbor hexagon. As a consequence the observed small magnetic hyperfine field gives access to second-neighbor and/or interplane interactions in the frustrated lattice.

• Received 31 October 1995

DOI:https://doi.org/10.1103/PhysRevLett.76.4829