Magnetic And Transport Properties Of Amorphous Carbon Films Doped With Rare Earth Metals

Amorphous carbon films doped with granular metals have important practical applications in optical devices,high density magnetic recording and magnetic sensors.Carbon atoms can form various structures in amorphous carbon.The sp2/sp3 ratio,which has strong effects on the optical and transport properties of amorphous carbon matrix,can be modulated by changing the fabrication conditions or doping rare earth metal.Gd/C granular films were fabricated by facing-target magnetron sputtering at room temperature and annealed at 300~650 oC.The diameter of Gd particles becomes larger with the increase of annealing temperature.Meanwhile,the annealing temperature leads to the aggregation and crystallization of Gd particles in a-C matrix.The Raman images indicate that the degree of graphitization rapidly increases when the annealing temperature is above 500 oC.The graphitization networks seem to bridge the Gd particle clusters.The MR ratio displays a sign change from negative to positive,then to negative with the increasing temperature.The tunneling conduction,wave function shrinkage and grain boundaries scattering effect dominate in different temperature regions and compete with each other at the boundaries of temperature regions.The range of positive MR can be expanded by annealing.The nonmagnetic rare earth metal Lu was doped into amorphous carbon matrix for excluding the effect of magnetic metals.The conduction mechanism is variable range hopping at the low temperatures(T ?(16)(15)(15)(42)).The room temperature conductivity increases rapidly after annealing.When the temperature falls in the range of 100~300 K(high temperature region),the conduction mechanism changes to grain boundaries scattering.The magnetoresistance of Lu/C granular films is dominated by different conduction mechanisms.The negative magnetoresistance is caused by grain boundaries scattering effect at high temperatures.Spin blockade effect causes the positive magnetoresistance of the Lu/C granular films,which becomes more obvious after annealing.