Study On The Doping Modification Of Silver Selenide Materials Of Large Positive Linear Magnetoresistance

The nonstoichiometric silver selenide(Ag2+δSe) with only a small amount ofexcess silver has been reported to possess very large linear magnetoresistance(LMR)in a very broad range of temperature(1K-300K) and magnetic field(1mT-60T) withno sign of saturating, this can not be explained by the classical transport theory of thenarrow-gap semiconductor. The present explanations for the mechanism behind thelarge LMR fall into two general categories: the quantum magnetoresistance and theclassical disorder model. The former emphasizes the zero-gap property and lineardispersion of the material, the magnetoresistance become linear with the field whenthe system reaches the quantum limitation, which means all the electrons coalesceinto the first Landau level; wheras the latter emphasize the disordered current in thematerial caused by the inhomogeneous structure, hence large fluctuations in mobilityarise, which directly leads to large LMR. The property of linear response to magneticfield make self-doped Ag2+δSe a promising candidate in magnetic sensor.In the previous studies of our group, the resistivity of Ag2+δSe was found too lowand the carrier density too high, which both lead to a high electrical noise, hence limitits application in magnetic sensor. In order to improve the application performance ofthe material, two series of Ag2Se based samples doped by indium and cobaltrespectively were prepared by the hydrothermal method. The indium doped sampleswere found to be Ag2Se-AgInSe2composite material by the X-ray diffraction andX-ray fluorescence method. The morphology of the samples was characterized byTEM and SEM, showing two kinds of grains with different sizes, corresponding toAg2Se and AgInSe2phases respectively. The cobalt doped samples were found to besubstitutional solid solution with cobalt atoms occupying mainly the AgIsite by theX-ray diffraction, X-ray fluorescence method and Rietveld profile refinement, themaximum solubility was found to be40%.At last, tranverse magnetoresistance(TMR) measurement was done on a series ofAg2Se-AgInSe2composite materials with different indium content, all samples exhibit a quadratic field dependence of TMR at low field and a linear and nonsaturating oneat high field up to50T, and TMR increases with decreasing indium content, themaximum was found to be400%, this should be attribute to the disorder in themacrostructure of the material, which is corresponding to the the classical disordermodel. The existenss of AgInSe2phase will increase the resistivity of the material,which can decrease the electrical noise in the application of magnetic fieldmeasurement, however the TMR will be decreased simultaneously. Therefore, addingan appropriate amount of AgInSe2phase can increase the performance of the materialin the magnetic field measurement.