Study On Magnetic Property And Modification Of Silver Selenide Doped By Magnetic Ion

Ag₂Se and Ag₂Te are multifunctional materials, high-temprature a-Ag₂Se ?Ag₂Te? is superionic conductor, low-temperature ?-phase Ag₂Se is a non-magnetic narrow-gap semiconductor and important thermochromics material. Normally, the magnetoresistance effect of ?-Ag₂Se and Ag₂Te is not noticeable, but, slightly altering the stoichiometry, Ag_2+?Se and Ag_2+?Te ?? is excess of Ag? will show noticeable positive linear magnetoresistance, and the linear magnetoresistance do not saturate in magnetic fields up to near 100T. As for this phenomenon, Abrikosov proposed a quantum MR ?QMR? in silver chalcogenides (Ag_2+?Se and Ag_2+?Te) based on the assumption of the gapless linear spectrum caused by metal Ag cluster. Parish and Littlewood thought that the spatial distribution of the charge carrier mobility were tuned by excess metal ions and eventually leaded to the unusual MR behaviors when the averaged mobility was zero. Zhang et al have speculated theoretically that silver chalcogenides may be a topological insulator based on first principles, so MR may come from highly anisotropic surface states.Co-doped Ag₂Se nanoparticles and Ni-dopped Ag₂Se have been prepared through solvothermal ?ethylenediamine or diethylamine? method by Yu et al, and good ferromagnetic properties were found in these material, so our work will continue the before, preparing Fe, Ni, Co-doped Ag₂Se by simple and safe hydrothermal method and studying their magnetic properties were expected.In our work, firstly, preparing a serial of Co-doped Ag₂Se nanorods and Ni doped Ag₂Se nanoparticles through simple and available hydrothermal method. Changing the concentration of NaOH to control the size of nanorods and nanoparticles; changing the ratio of Ag and CoCl2·6H2O?NiCl2·6H2O? to adjust the solubility of Co?Ni? in Ag₂Se lattice. Lastly, determined the optimum experimental scheme, i.e., when the concentration of NaOH is 0.9mol/l and 1.0mol/l, the ratio of Ag and Co?Ni? is 9:1 and 8:2, the samples are the best.A serial characterizations were implemented for all of the samples, such as XRD, XRF, SEM, XPS, UV-Vis and TG-DTA. The result of UV-Vis release that Co-doped Ag₂Se materials are narrow-gap semiconductors. For the most pure samples, temperature dependence of dc zero-field-cooling?ZFC? and field-cooling?FC? magnetizations under 500 Oe were implemented. Among the Co doped Ag₂Se nanorods, the solubility of Co of the most pure samples is up to 26.62%. For the pure Co doped Ag₂Se nanorods, Co element exists in Ag₂Se lattice in the form of Co2+ mainly. The normalized magnetic moment of per Co atom of the nanorods synthesized under 0.8M NaOH is up to 0.01594?B·Co-1 at 2.92K. With the increase of the concentration of NaOH, the normalized magnetic moment of per Co atom decreased. All the samples tested undergo a magnetic phase transition. The Ni-doped Ag₂Se prepared by hydro thermal method are nanoparticles, but little NiSe2 and Ag were found in the samples. The solubility of Fe in Fe-doped Ag₂Se prepared by hydrothermal method is not very high.