title: Low-temperature activation and deactivation of high-Curie-temperature ferromagnetism in a new diluted magnetic semiconductor: Ni2+-Doped SnO2.
abstract: We report the synthesis of colloidal Ni(2+)-doped SnO(2) (Ni(2+):SnO(2)) nanocrystals and their characterization by electronic absorption, magnetic circular dichroism, X-ray absorption, magnetic susceptibility, scanning electron microscopy, and X-ray diffraction measurements. The Ni(2+) dopants are found to occupy pseudooctahedral Sn(4+) cation sites of rutile SnO(2) without local charge compensation. The paramagnetic nanocrystals exhibit robust high-Curie-temperature (T(C)) ferromagnetism (M(s)(300 K) = 0.8 mu(B)/Ni(2+), T(C) >> 300 K) when spin-coated into films, attributed to the formation of interfacial fusion defects. Facile reversibility of the paramagnetic-ferromagnetic phase transition is also observed. This magnetic phase transition is studied as a function of temperature, time, and atmospheric composition, from which the barrier to ferromagnetic activation (E(a)) is estimated to be 1200 cm(-1). This energy is associated with ligand mobility on the surfaces of the Ni(2+):SnO(2) nanocrystals. The phase transition is reversed under air but not under N(2), from which the microscopic identity of the activating defect is proposed to be interfacial oxygen vacancies.
authors.affiliation: Department of Chemistry, University of Washington, Seattle, WA 98195-1700, USA.
authors.forename: Paul I
authors.initials: PI
authors.lastname: Archer
authors.forename: Pavle V
authors.initials: PV
authors.lastname: Radovanovic
authors.forename: Steve M
authors.initials: SM
authors.lastname: Heald
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Gamelin
mesh_terms: D003102:Colloids / Q000138:chemical synthesis / Q000737:chemistry; D003460:Crystallization; D008280:Magnetics; D049329:Nanostructures / Q000737:chemistry; D009532:Nickel / Q000737:chemistry*; D012666:Semiconductors; D013696:Temperature; D013997:Time Factors; D017971:Tin Compounds / Q000737:chemistry*
chemical_list: D003102:Colloids; D017971:Tin Compounds; D009532:Nickel; C045358:stannic oxide