RENORMALIZATION GROUP CALCULATIONS FOR THE DILUTE HEISENBERG MAGNET

A position-space renormalisation group calculation based on the Migdal approximation is presented for a randomly diluted Heisenberg magnet. A crossover from percolative to thermal critical behaviour was found at low temperatures and the associated crossover exponent has been calculated. To investigate the behaviour at higher temperatures, an approximate recursion formula was used for the spin system. The calculated variation in the reduced Curie temperature with the concentration of impurities is in fairly good agreement with series-expansion results.