An anomaly in the magnetic susceptibility of the Mg1-xCuxO solid solutionswith 0.01 <= x <= 0.20

The problem of localized superconductivity has motivated the preparation of Mg1-xCuxO solid solutions with NaCl structure and 0.01 less than or equal to x less than or equal to 0.20, as well as a study of the magnetization an d magnetic susceptibility chi in the 2-400 K temperature range and in magne tic fields of up to 5 T. The temperature dependence of chi is described for all compositions by the Curie-Weiss law, chi = C/(T - theta), where the co nstant C is close to the value calculated for each composition for mu(eff) = 1.7-1.9 mu(B) , and theta is close to zero. For T < 30 K, chi(T) deviates for all compositions toward lower chi, which can be attributed to magnetic ordering of exchange-coupled clusters in the solid solution. At T similar to 320-330 K, an anomaly of a diamagnetic type, i.e., a decrease of chi by 6-30% of its paramagnetic value, has been observed for all compositions aga inst the background of the generally paramagnetic chi(T). A discussion is p resented of alternative reasons for this anomaly and of its possible connec tion with localized superconductivity. (C) 2000 MAIK "Nauka/ Interperiodica ".