Thespinelferritenanoparticlesdue tocharacteristicssuch ashigh permeabilityandlow coercivity,have beenwidely usedinindustryand medicine.But, a simple,reproducibleand low cost fabrication method by whichmagnetic nanoparticlesaresynthesizedwithhighhomogeneity andpurityhasalwaysbeen aconcern ofresearchers. Therefore,inthis study, nanocrystallineNi x Zn 1-x Fe 2 O 4 ferrites,themost commonly usedmagneticmaterials among the spinel ferrites, have been synthesized via sol–gel auto-combustion method usingEDTA as a complexion agent, thatpreventsoxidationand interaction ofmetal cationswiththesurroundingions and causes the formation of finer particles. Thisstudyconsists of threeparts. In thefirst part,we have investigated the effect of Znsubstitutiononstructureand magneticpropertiesof nickelferrite and in the second part,the effect of sinteringtemperatureand thenin thethird part, the effect of polyvinyl alcohol (PVA) coating on structural, magnetic properties and spin dynamics of Ni 0.3 Zn 0.7 Fe 2 O 4 ferrite nanoparticles have been studied usinganalysissuch asX-ray diffraction(XRD),Furier Transform Infrared(FTIR),microscopic imaging(FE-SEM)and(TEM),vibrating sample magnetometer (VSM)andac susceptibility measurements. The XRD patterns indicated that the crystalline structure is single phase cubic spinel for all samples and the MAUD results indicate that the synthesized nickel ferrite (NiFe 2 O 4 ) and the zinc ferrite (ZnFe 2 O 4 ) nanocrystals have inverse and normal spinel structure, respectively. Ni 1-x Zn x Fe 2 O 4 ferrites (0 x 1) have a mixed spinel structure. TheVSM data showed that by increasing Zn doping level up to x = 0.3, the magnetization was increased and it was decreased by further increase in x ,due to the weakening of the superexchange interaction at the octahedral sites.The magnetocrystalline anisotropy constant of Ni ferrite is larger than that of Zn ferrite. Therefore, the magnetocrystalline anisotropy constant decreases with the replacement of Zn 2+ ion by Ni 2+ ion, which implies an decrease in H c .The XRD patterns of the samplesannealedat different temperatures350-1200 °C,showed the peaks width reduces by increasing sintering temperature indicating the crystallite size enhancement during sintering process at elevated temperatures. Saturation magnetization ( M s )increaseswith increasingsinteringtemperature andcanbecaused due tothree reasons: (1)In the larger nanoparticles, high crystallinity and a low amount of microstructure defects allow domain walls to move easily in the magnetization process, (2) In the Core-shell morphology, the higher core/shell ratio of large particles leads to eliminations of surface effects and consequently enhancement of M s and (3) by increasing the sintering temperature, the extra Fe 3+ ions in the A sites, start distributing into the B sites and hence the number of Fe 3+ ions at A site is reduced. Consequently, the n B increases with increasing sintering temperature due to a decrease in fraction of magnetic moment of A site and an increase in the net magnetic moment of B sites. Of course, thethirdreason was confirmed byfitting ofXRDpatterns using theMAUDsoftware. XRDpatterns oftwo samples withand withoutPVAannealedat 375°Cindicated that the crystalline structure is single phase cubic spinel and in which the spinel structure is retained after PVA coating and the increase in M s after PVA coating could be attributed partly to the nanoparticle’s crystal growth after polymer coating. The analysis of acsusceptibilitycurveswith critical slowing down model showed that, the interparticle interaction leads to the superspin glass-likebehavior in these nanoparticle samples. Key words: Spinel ferrites, Sol-gel, EDTA, Znsubstitution effect, Temperature effect, Cation distribution, Core-shell model, Critical size, PVA.