INVESTIGATION OF MAGNETITE THIN-FILMS PRODUCED BY PULSED-LASER DEPOSITION

Thin films of magnetite (Fe3O4) with thicknesses in the range 10-1000 nm have been produced by the XeCl excimer laser (lambda = 308 nm) abla tion of both Fe3O4 and metallic Fe-57 targets. Deposition conditions h ave been investigated in an attempt to fabricate films reproducibly at low laser fluences so as to minimize ablation bouldering. The ablatio n 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 betwee n the two target materials. The use of single-crystal, lattice-matchin g substrates was found to be necessary at lower fluences (1-3 J cm(-2) ) for the ablation of metallic Fe, whereas polycrystalline, non-lattic e-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 be en established that the films produced from a metallic target containe d a significant amount of metallic Fe, together with secondary oxide p hases. The influence of him thickness on the Verwey transition has bee n investigated via electrical conductivity and SQUID magnetometry. It is found that there is a systematic reduction of Verwey temperature wi th decreasing film thickness; this is attributed to the effect of stra in. (C) 1997 Elsevier Science B.V. All rights reserved.