In this work, we are showing the results of the X- and Q-band electron magnetic resonance measurements of ultra-small Zn1-xMnxFe2O4 nanoparticles (ca. 8 nm) with a very narrow size distribution. The chosen synthetic route allows for precise structural modifications with a broad concentration range (x = 0, 0.2, 0.5, 0.8, 1). The crystal structure was evaluated by means of X-ray diffraction, while cell parameters were calculated using Rietveld refinement. EMR spectral studies indicated that the prepared nanoparticles were superparamagnetic. The linewidth of EMR signal for any ferrite material generally originates from two sources: (a) magnetic dipole-dipole interactions among particles and (b) interparticle superexchange interactions between magnetic ions through oxygen ions. Observed effects are more complex interactions than in pure zinc and manganese ferrites. As a result of the study, a relationship was observed between the composition of the material and the magnetic properties with striking antiferromagnetism and ferrimagnetism change. Hence, by structural modification of materials, the magnetic character (FM-AFM-FiM) can be controlled.