Magnetic and structural investigations on as-grown and oxygen annealed PLD SnO2 : Co thin films

Abstract

Detailed structural and magnetic characterization has been performed on dilute magnetic oxide SnO2 : Co thin films deposited on R-cut sapphire substrates via pulsed laser deposition from a doped target of 5 at.% nominal Co concentration. These studies demonstrate that the films are highly crystalline, composed of single phase SnO2 : Co grains, with no formation of Co nanoclusters in the oxide matrix, and are ferromagnetic at room temperature. It was found that ferromagnetism and electrical conduction are strongly dependent on the growth rate, film thickness and post deposition annealing protocols and suggest that the magnetic properties are related to the number of defects, and thus the crystallinity of the films. For thicknesses above 70 nm, films are electrically conducting and ferromagnetic, with a relatively constant MS of about 20 emu cm−3 at room temperature. Moreover, the moment per unit area varies linearly with the film thickness, showing that the ferromagnetism of the studied materials is a volume property. Samples annealed in conditions similar to their growth display a dramatic increase of MS in the first 5 min of annealing. Temperature dependent magnetization measurements reveal that approximately one third of the cobalt couples ferromagnetically with the remaining two thirds existing in the form of paramagnetic isolated cobalt spins. Experimental evidence supports the conclusion that films are formed of single crystal grains of SnO2 doped with Co, held together by defect-rich grain boundaries.