Effective critical behaviour of diluted Heisenberg-like magnets

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In agreement with the Harris criterion, asymptotic critical exponents of three-dimensional (3d) Heisenberg-like magnets are not influenced by weak quenched dilution of non-magnetic component. However, often in the experimental studies of corresponding systems concentration- and temperature-dependent exponents are found with values differing from those of the 3d Heisenberg model. In our study, we use the field--theoretical renormalization group approach to explain this observation and to calculate the effective critical exponents of weakly diluted quenched Heisenberg-like magnet. Being non-universal, these exponents change with distance to the critical point Tc as observed experimentally. In the asymptotic limit (at Tc) they equal to the critical exponents of the pure 3d Heisenberg magnet as predicted by the Harris criterion.