Dopant distribution, oxygen stoichiometry and magnetism of nanoscale Sn_0.99Co_0.01O₂

In recent work, we have shown that chemically synthesized Sn_1-xCo_xO₂ nanoscale powders with x ≤ 0.01 are ferromagnetic at room temperature when prepared by annealing the reaction precipitate in the narrow temperature window of 350-600 ^{{ring operator}}C. Combined high resolution x-ray photoelectron spectroscopy (on as-prepared and Ar⁺ ion sputtered samples), x-ray diffraction and magnetometry measurements showed that the Co distribution is more uniform throughout the individual Sn_0.99Co_0.01O₂ particles when prepared at lower annealing temperatures of 350-600 ^{{ring operator}}C and this uniform dopant distribution is essential to produce stable high temperature ferromagnetism. However, surface segregation of the dopant atoms in samples annealed at >600 ^{{ring operator}}C destroys the room-temperature ferromagnetic behavior and reduces the Curie temperature to <300 K.