New measurement of the critical exponentβfor nickel by microwave transmission

We measure the critical exponent β for spontaneous magnetization in thin foils of polycrystalline and single-crystal nickel, with results, β=0.357±0.008 for a reduced temperature range of 10^-2<ε<10^-1 and 0.358 ±{} 0.003 for a reduced temperature of 5×10^-3<ε<10^-1, respectively. These values lie significantly lower than values obtained by such nuclear hyperfine probe methods as angular correlation and M\"ossbauer absorption, and somewhat larger than values obtained by applied-field methods extrapolated to zero or NMR methods. Since this experiment employs "zero applied field" resonance observed by microwave transmission at 9.232 GHz and requires a theory to relate the resonance signal to the magnetization, we discuss the question of fit to theory, determination of necessary parameters, etc., and conclude that the errors quoted here are statistical and not theory dependent. We determine a value for the critical amplitude B of 1.27 ±{} 0.03 and 1.23 ±{} 0.02 for the two samples, respectively.