  We report 75As-nuclear quadrupole resonance (NQR) studies on
(Ca_4Al_2O_{6-y})(Fe_2As_2) with Tc=27K, which unravel unique normal-state
properties and point to unconventional nodeless superconductivity (SC).
Measurement of nuclear-spin-relaxation rate 1/T_1 has revealed a significant
development of two dimensional (2D) antiferromagnetic (AFM) spin fluctuations
down to Tc, in association with the fact that FeAs layers with the smallest
As-Fe-As bond angle are well separated by thick perovskite-type blocking layer.
Below Tc, the temperature dependence of 1/T_1 without any trace of the
coherence peak is well accounted for by an s(+-)-wave multiple gaps model. From
the fact that Tc=27K in this compound is comparable to Tc=28K in the
optimally-doped LaFeAsO_{1-y} in which AFM spin fluctuations are not dominant,
we remark that AFM spin fluctuations are not a unique factor for enhancing Tc
among existing Fe-based superconductors, but a condition for optimizing SC
should be addressed from the lattice structure point of view.
