  Quantum criticality of the spin-1/2 ferromagnetic-leg ladder 3-I-V
[=3-(3-iodophenyl)-1,5-diphenylverdazyl] has been examined with respect to the
antiferromagnetic to paramagnetic phase transition near the saturation field
$H_{c}$. The phase boundary $T_{c}(H)$ follows the power-law $T_{c}(H)\propto
H_{c}-H$ for a wide temperature range. This characteristic behavior is
discussed as a quasi-one-dimensional (quasi-1D) Bose-Einstein condensation,
which is predicted theoretically for weakly coupled quasi-1D ferromagnets.
Thus, 3-I-V provides the first promising candidate for this attractive
prediction.
