PERTURBED-ANGULAR-CORRELATION MEASUREMENTS IN 2D SPIN-FRUSTRATED CUFEO2

We report on first perturbed angular correlation (PAC) measurements in the 2D triangular antiferromagnet CuFeO2. The implanted In-111 PAC pr obes resides on Fe sites and sense the combined hyperfine interaction of the structural electric field gradient and an antiferromagnetic int ernal field which is surprisingly small as compared to other ferromagn etic or antiferromagnetic oxides. This is explained by a local change in the frustrated triangular lattice leads to a perfect cancellation o f the magnetic hyperfine fields of the probe's next-neighbor hexagon. As a consequence the observed small magnetic hyperfine field gives acc ess to second-neighbor and/or interplane interactions in the frustrate d lattice.