WEAK FERROMAGNETISM IN Zn 1-X Co X O
To study the origin of ferromagnetism in Zn 1-x Co x O thin films the thermal diffusivity, additionally, to the magnetization
measurements has been conducted. The thin films of Zn 1-x Co x O (x = 0.03) were deposited on Si (100) substrate by using
ultrasonic spray pyrolysis. Magnetization M(H) measurements at low temperature show a hysteresis loop which indicates an
existence of ferromagnetic ordering in Zn 0.97 Co 0.03 O. However, the magnetic moment per Co ion is much lower than expected.
A comparison of M(T) measured at zero-field-cooled (ZFC) and field-cooled (FC) conditions shows a superparamagnetic- like
behavior and the blocking temperature is about 130K. Temperature dependence of the thermal diffusivity of Zn 0.97 Co 0.03 O
shows a pronounced lambda shaped minimum at 130K, which indicates an existence of a second-order phase transition at this
temperature. The weak ferromagnetism in the Zn 0.97 Co 0.03 O with the Curie temperature of 130 K is ascribed to the
uncompensated magnetic moment at the surface of CoO nanoclusters.
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