Modification of magnetic ferrite nanoparticles (NPs) could open new avenues for their applications in many fields. SnxFe3-2x/3O4 NPs were synthesized using precipitation under reflux by Sn2+ doping (x = 0.000-0.150) and characterized using a host of morphological, structural, magnetic, and surface characterization techniques. Sn2+ doping increases the NPs-size (12-50 nm) and protects them from oxidation and transformation to the -Fe2O3 phase, thus making them more suitable for many applications. From Rietveld refinement data, dopant Sn2+ ions, while preferentially occupying the B sites at equilibrium, initially started with A site occupation. The randomly-oriented spins on the surface of these nanoparticles, together with oxidation to maghemite, explain the observed decrease in magnetization for Fe3O4 nanoparticles, but not for the doped samples, where spin canting in B sites was preferred. In addition, an unusual and new magnetic feature was found after high-temperature annealing of these NPs. Detailed characterizations during the heating-cooling cycles revealed the possibility of tuning the unusual observed magnetization dipping temperature/amplitude, irreversibility, and Curie point of these NPs by doping with Sn2+. A phenomenological expression that combines both modified Bloch law and a modified Curie–Weiss law was developed to explain the observed M-T behaviors. Additionally, hydrothermally-synthesized needle-shaped Sn2+ doped uncoated and C-coated α-Fe2O3 nanorods (NRs) (Sn2+ % of 0, 1.5, 3, and 5%) were observed to be destroyed in shape by Sn2+ doping. By calcination (600 C), the shape of the nanorods is retained. The magnetic study (at a temperatures range of 2-900 K, and fields from 10 to 200 Oe,showed field-dependent magnetization at the same warming– cooling rates, thermal hysteresis (15-30 K) of the Morin temperature, and Sn2+ dependent susceptibility. In this study, we explain the suppression of the Morin transition for nanosized particles with c/a of  2.74. Furthermore, the evaporation technique was used to synthesis iron-based nanoclusters (NCs) and make an iron-coating layer, on MWCNTs and Si substrates. The Fe/MWCNTs NCs were found to be large, forming a core/shell structure. An electron transfer between NCs and MWCNTs was evident. A shift in the binding energy of XPS core ionization levels and the valence band maximum (VBM) were observed, confirming the formation of a semi-metallic phase. The saturation magnetization increased five times in clustering, compared to coating with a noticeable negative exchange bias in the Fe/Si coated sample.