Local critical behavior in the Ni -Ta system

We compare the critical behavior of the hyperfine field on tantalum nuclei in a nickel matrix and the critical behavior of the bulk magnetization of the matrix itself. The hyperfine critical exponents are βₕ=0.407±0.003 and δₕ=4.6±0.3, whereas the macroscopic critical exponents measured on the same series of samples are β=0.379±0.003 and δ=4.48±0.09. The hafnium content was very low ({} 1 at.ppm) and the nickel was very pure. Therefore, we think that this discrepancy between the critical exponents βₕ and β must be explained in the framework of a one-impurity model.