Magnetic properties of oxidized iron thin films grown by sputtering at very low temperatures

Iron thin films have been grown by DC magnetron sputtering using Si(100) wafers as substrates, and then oxidized in a well-controlled oxygen atmosphere in the vacuum chamber. Film thickness is about 50 nm, and grains forming these samples do not exceed 20 nm. In order to control structural properties such as size and shape of these grains, growth conditions can be modified, like deposition rate or substrate temperature, varying from 150 to 300 K. Two sets of samples have been prepared considering deposition rate: (i) films grown at 0.6 nm/min and (ii) at 1.2 nm/min. In order to prevent iron films from natural oxidation, all the sample series were covered with a gold layer. Analysis of their magnetic behaviour shows a strong dependence on grain size and temperature, resulting in a more effective oxidation for samples prepared at higher deposition rates and lower substrate temperatures, which behaves as a Fe/Fe oxide granular system.