Investigation On The Ferromagnetism Origination And Related Properties Of Magnetic Ions Doped CeO₂

Diluted magnetic semiconductor (DMS) is a key material for spintronics andrelated devices.Via this type of functional materials,the spins of electrons can beutilized,as the spin transportation and spin injection would be realized.Especially therecently developed diluted magnetic oxide,its high curier temperature (T_C) which iswell above room temperature,via which spin filtering-effect can be realized at roomtemperature,fundamentally facilitate the progress of spintronic-related devices onpractical aspect,and thus this field is being paid more and more attentions.Firstly,based on first principle calculations,several transitional elements (such as V,Cr,Mn,Fe,Co,Ni) doped CeO₂ systems are investigated with LDA+U methods in WIEN2kpackage.By calculating the electronic structure and density of state,the doped systemswith ferromagnetism (FM) are predicted,and the exchange coupling mechanism amongthe doped magnetic ions are further investigated,mainly focusing on the oxygenvacancy (V_O) related ferromagnetic exchange coupling mechanism.It is found thatmagnetic ions forms ferromagnetic coupling via Vo,which is well consistent withVo-induced ferromagnetic exchange coupling mechanism.And then from experimentalaspects,doped CeO₂ bulk and thin films with different elements and varied dopingcontents are synthesized by equilibrium methods (including solid-state reaction) andnon-equilibrium methods (including magnetron sputtering,pulsed laser deposition-PLD,and E-beam evaporation).With varied technology parameters and adopted postannealing,magnetic properties,micro-morphologies,as well as X-ray photoelectronspectroscopy (XPS) and Raman spctra of different samples are measured,to investigatethe influential factors for room temperature (RT)- FM.It is found experimentally thatthe FM is best for samples with the stoichiometry of Ce_0.97Co_0.03O_2-δ,with a highestCurier temperature of 625K and 760K for its bulk and thin films,respectively.The V_Orelated FM can be well explained by Vo-induced ferromagnetic coupling mechanism,and further experiments of co-doping and Ar⁺-bombardment methods are carried out forfurther investigation.At last,a three layered- structure of Ni(80nm)/Ce_0.97Co_0.03O_2-δ(dnm)/Co₅₀Fe₅₀(80nm) with viaried thickness of the inter layer (d=1,3,5,10 nm, respectively) are fabricated via four-targes magnetron sputtering system.Magneticresistance measurements indicate a 5% MR value in the sample with d=5nm thickness.This results provide a provement of the RT-spin filtering effect of Ce_0.97Co_0.03O_2-δ thinfilms,exhibiting a wide potential applications in spin-related devices.