Ssc. Burnett et S. Gartenhaus, PHENOMENOLOGY, SPECIFIC-HEAT, AND CORRECTIONS TO SCALING IN COPPER AMMONIUM BROMIDE, Physical review. B, Condensed matter, 49(2), 1994, pp. 1137-1145
Experimental data near the critical point for the spontaneous magnetiz
ation, the zero-field susceptibility, and the specific heat of the (S
= 1/2) insulating Heisenberg ferromagnet Cu (NH4)(2)Br(4)2H(2)O are co
mpared with two extensions of asymptotic scaling. One is a previously
described phenomenology which is equivalent to the predictions of the
renormalization group (RG) when all irrelevant variables are neglected
. The second results if one adds to the asymptotic scaling formulas th
e confluent singularities due to the leading irrelevant variable. We f
ind that both sets of formulas are consistent with the data for all th
ree quantities: the spontaneous magnetization, the aero-field suscepti
bility, and the specific heat, but that overall, the phenomenology req
uires fewer parameters. A discrepancy between the experimental and the
oretical values for the susceptibility exponent. is discussed.