Phase diagram of ZnCr2pAl2-2pS4 and Zn1-pCdpCr2Se4

We compute the phase diagram of the non-metallic compounds ZnCr2pAl2-2pS4 ( I) and Zn1-pCdpCr2Se4 (II). We consider the bond-diluted Ising model on the spinel B site (S.B.S.) lattice with competitive exchange interactions, i.e . the ferromagnetic exchange interaction J(1) between nearest neighbours (n .n.) and the antiferromagnetic superexchange interaction J(2) between next- nearest neighbours (n.n.n.) (or and the more distant superexchange interact ions J(i) (i > 1)). Dilution and competition are found to be responsible of the spin glass phase and the percolation behaviour.