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.