Inthisstudy,nanocrystallineCo–Ni–MgferritepowderswithcompositionCo0.5Ni0.5-xMgxFe2O4aresuccessfullysynthesizedbytheco-precipitationmethod.Asystematicinvestigationonthestructural,morphologicalandmagneticpropertiesofun-dopedandMg-dopedCo–Niferritenanoparticlesiscarriedout.Thepreparedsamplesarecharacterizedusingx-raydiffraction（XRD）analysis,Fouriertransforminfraredspectroscopy（FTIR）,fieldemissionscanningelectronmicroscopy（FESEM）,andvibratingsamplemagnetometry（VSM）.TheXRDanalysesofthesynthesizedsamplesconfirmtheformationofsingle-phasecubicspinelstructureswithcrystallitesizesinarangeof32nmto36nm.ThelatticeconstantincreaseswithincreasingMgcontent.FESEMimagesshowthatthesynthesizedsamplesarehomogeneouswithauniformlydistributedgrain.TheresultsofIRspectroscopyanalysisindicatetheformationoffunctionalgroupsofspinelferriteintheco-precipitationprocess.ByincreasingMg2+substitution,roomtemperaturemagneticmeasurementshowsthatmaximummagnetizationandcoercivityincreasefrom57.35emu/gto61.49emu/gand603.26Oeto684.11Oe（1Oe=79.5775A·m-1）,respectively.ThehighervaluesofmagnetizationMsandMrsuggestthattheoptimumcompositionisCo0.5Ni0.4Mg0.1Fe2O4thatcanbeappliedtohigh-densityrecordingmediaandmicrowavedevices.
