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The form of the magnetic isothermals of a bulk specimen of the ferrite CoO 0.18 ZnO 0.75 Fe 2 O 3 between 77° K and room temperature indicates the presence of strongly magnetic particles of maximum diameter about 40 Å in a superparamagnetic state dispersed in a non-magnetic matrix. Cooling in an applied field down to 4.2° K produces a displaced hysteresis loop characteristic of unidirectional exchange anisotropy. The coercivity at 4.2° K after cooling in zero field is about 5000 Oe.
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Booth et al. (1962) studied this question.
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