Investigation of magnetite thin films produced by pulsed laser deposition

Abstract

Thin films of magnetite (Fe 3O 4) with thicknesses in the range 10–1000 nm have been produced by the XeCl excimer laser ( λ = 308 nm) ablation of both Fe 3O 4 and metallic 57Fe targets. Deposition conditions have been investigated in an attempt to fabricate films reproducibly at low laser fluences so as to minimize ablation bouldering. The ablation of metallic Fe has been shown to produce a smaller concentration of boulders than the ablation of bulk magnetite. It is believed that this is mainly due to the difference in primary ablation mechanisms between the two target materials. The use of single-crystal, lattice-matching substrates was found to be necessary at lower fluences (1–3 J cm −2) for the ablation of metallic Fe, whereas polycrystalline, non-lattice-matching substrates were adequate for deposition with moderate laser fluences (5–6 J cm −2). Film quality has been assessed by a range of techniques including XRD, SEM, AFM/MFM and CEMS. Using CEMS it has been established that the films produced from a metallic target contained a significant amount of metallic Fe, together with secondary oxide phases. The influence of film thickness on the Verwey transition has been investigated via electrical conductivity and SQUID magnetometry. It is found that there is a systematic reduction of Verwey temperature with decreasing film thickness; this is attributed to the effect of strain.