Dopant distribution, oxygen stoichiometry and magnetism of nanoscale Sn0.99Co0.01O2

In recent work, we have shown that chemically synthesized Sn1-xCoxO2 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 degrees 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 Sn0.99Co0.01O2 particles when prepared at lower annealing temperatures of 350-600 degrees 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 degrees C destroys the room-temperature ferromagnetic behavior and reduces the Curie temperature to < 300 K. (c) 2006 Elsevier Ltd. All rights reserved.