XRD, HRTEM and magnetic properties of mixed spinel nanocrystalline Ni-Zn-Cu-ferrite

Nanocrystalline Ni0.4Zn0.4Cu0.2Fe2O4 Samples with different particle sizes are prepared by simple co-precipitation method. The mixed spinel phases of the nanocrystalline materials have been confirmed by X-ray diffractograms (XRD). The sizes of the nanoparticles are estimated from the (3 1 1) peaks of the XRD patterns using Debye-Sherrer equation and are lying in the range of 7-32 nm. High-resolution TEM observations also support the findings obtained from XRD. Specific saturation magnetizations measured by vibrating sample magnetometer (VSM) are found to increase steadily with the increase of average particle size. Nature of variations of the magnetization curves of the different particle sizes samples are of typical superparamagnetic behaviours up to 16 nm beyond which ferrimagnetic ordered particles are dominating over superparamagnetic particles. The coercive field for a sample of particle size 12 rim is interestingly low (87 A/m) where the saturation magnetization is also moderately high (similar to 50 A m(2)/kg). The coercive fields of the different samples obtained from low frequency hysteresis loops observations show that even in case of sample with lowest particle size, a small fraction of particles are not relaxed within the experimental time window. (C) 2008 Elsevier B.V. All rights reserved.