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Ultrafine particles of nickel-zinc ferrite have been formed from solutions of metal nitrates by coprecipitation with hydrazine, foHowed by aging at 90 DC. The crystallites either aggregate into much larger dusters or form single particles, depending upon the preparation conditions, and vary in size from 30 to z 300 A. Saturation magnetizations (Ms) of the ferrites varied from 40 to 65 emu/g and the coercivities from 1 to z 100 Oe. Increasing hydrazine concentrations tended to produce particles with lower M,. However, for hydrazine/metal ratios below unity, decreasing the hydrazine concentration dramatically lowered the M, value. Particles formed without hydrazine (e.g., by aging hydroxides precipitated with potassium hydroxide) did not appear to be magnetic. Variations of the magnetic properties and lattice parameters as a function of preparation conditions will be discussed.3786

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