Effect of Heat Treatment on the Magnetic Properties of Hydrothermally Grown ZnO Crystals

ISSN： 0020-1685

Source： Inorganic Materials, Vol.39, Iss.10, 2003-10, pp. : 1052-1057

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Abstract

The magnetic susceptibility of ZnO single crystals annealed in vacuum, in an oxygen atmosphere, and in the presence of Li₂CO₃ is measured from 4.2 to 300 K. The susceptibility versus temperature curves of the crystals are similar in shape and differ by a roughly constant value, which is interpreted in terms of Van Vleck (temperature-independent) paramagnetism. The anomalies found below 30 K are due to paramagnetic defects such as Li_Zn and V_O, whose concentration depends on the growth and annealing conditions. Some other features of the susceptibility data are attributable to exchange interactions in X_i V_Zn (X = Zn, Si), Li_ZnZn_i , and V_OLi_Zn donor–acceptor pairs, which lead to magnetic saturation in the corresponding defect subsystem. The effect of annealing on the 300-K susceptibility of the crystals is attributable to Van Vleck paramagnetism, which results from the mixing of the ground and excited electronic states caused by defect-induced local strain fields.