Study of Weak Ferromagnetism in Zn[sub 1-x]Co[sub x]O

The temperature dependencies of the magnetization and the thermal diffusivity of Zn1‐xCoxO have been conducted. Zn1‐xCoxO (x = 0.03) thin films were deposited on Si (100) substrates by using ultrasonic spray pyrolysis. Magnetization M(H) measurements show a hysteresis loop which indicates an existence of ferromagnetism in Zn0.97Co0.03O. 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 Zn0.97Co0.03O shows a pronounced λ shaped minimum at 130K, which indicates an existence of a second‐order phase transition at this temperature. The low value of the phase transition entropy shows that only a small part of Co ions is involved in ferromagnetic ordering.

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