SITE-BOND CORRELATIONS IN THE 3-DIMENSIONAL HEISENBERG-MODEL - APPLICATION TO KNIPMG1-PF3

Site-bond-correlated dilution pictures have been successfully proposed to account for the striking differences experimentally observed by nu clear-magnetic-resonance (NMR) measurements between random-diluted KNi pMg1-pF3 and the isostructural system KMnpMg1-pF3. The present work ma kes use of a variational principle for the free energy to treat the cr itical behavior of the system KNipMg1-pF3 in the three-dimensional Hei senberg model by considering the interaction of the nearest neighbor a nd next-nearest neighbor in the spin system. The calculated phase diag ram in the T-p plane for the Heisenberg model is in good accordance wi th experimental data obtained by NMR, and the value of the correlation parameter is estimated.