Percolation limit and stability conditions for the spin glass state in the spinel families based on the two matrices CuCr(2)S(4) and CuCr(2)Se(4) doped by Sb ions

The percolation limit of the appearance of the spin glass state in the compounds under study has been obtained experimentally. The conditions of stability of the spin glass state have been analyzed here on the basis of the de Almeida-Thouless theory for two spinels differing in the magnetic coupling constants. It turned out that for the higher value of the coupling constant the magnetic field influences the freezing temperature more strongly. Moreover, the greater the coupling constant the broader the range of the possible values of freezing temperatures, in other words the greater the temperature range of the appearance of the spin glass states. It was proved that for the stability of the spin glass state the existence of a small magnetic field is necessary. In our case the value of this field is equal to 3.46 × 10(-23)T(G). For the compounds under study the value of the magnetic coupling constant J cannot exceed 130 K for the spin glass state to appear.