  In order to investigate physical properties around a ferromagnetic (FM)
quantum transition point and a tricritical point (TCP) in the
itinerant-electron metamagnetic compound UCoAl, we have performed the $^{59}$Co
nuclear quadrupole resonance (NQR) measurement for the Fe-substituted
U(Co$_{1-x}$Fe$_x$)Al ($x$ = 0, 0.5, 1, and 2%) in zero external magnetic
field. The Fe concentration dependence of $^{59}$Co-NQR spectra at low
temperatures indicates that the first-order FM transition occurs at least above
$x$ = 1%. The magnetic fluctuations along the $c$ axis detected by the nuclear
spin-spin relaxation rate $1/T_2$ exhibit an anomaly at $T_\mathrm{max}$ $\sim$
20 K and enhance with increasing $x$. These results are in good agreement with
theoretical predictions and indicate the presence of prominent critical
fluctuations at the TCP in this system.
