Single-phase nanoparticles of MnZnFe O (MZF) with improved magnetic properties were prepared from the precursor (formed by chemical route) by microwave processing technique at 500 C in only 3 min. Crystallographically, these were found to be of spinel phase. Using Debye-Scherrer formula, the particle size of conventionally sintered powder is estimated to be about 20 nm, whereas that of microwave processed is nearly 50 nm with improved grain size. The field emission scanning electron (FESEM) and transmission electron (TEM) micrographs revealed the particles in microwave-processed samples to be spherical in shape and confirmed the sample size (to be nearly 50 nm). Room temperature magnetization measurement of conventionally sintered samples (by vibrating sample magnetometer (VSM)) showed their superparamagnetic nature with saturation magnetization of nearly 19 emu/g. The microwave-processed samples showed improved saturation magnetization of nearly 36 emu/g, which is even better than the reported value. [ABSTRACT FROM AUTHOR]