  We study the Cr_(1-x) Re_x phase diagram finding that its phase transition
temperature towards an antiferromagnetic order T_N follows a quantum
[(x_c-x)/x_c ]^{\psi} law, with {\psi}=1/2, from the quantum critical point
(QCP) at x_c=0.25 up to T_N=600K. We compare this system to others in order to
understand why this elemental material is affected by the QCP up to such
unusually high temperatures. We determine a general criterion for the
crossover, as function of an external parameter such as concentration, from the
region controlled solely by thermal fluctuations to that where quantum effects
become observable. The properties of materials with low coherence lengths will
thus be altered far away from the QCP.
