Physical properties of spinel iron oxide thin films
- PDF / 866,094 Bytes
- 7 Pages / 593.28 x 841.68 pts Page_size
- 58 Downloads / 231 Views
I. INTRODUCTION There is general interest in developing thin-film magnetic storage media with the goal of increasing the storage density. Two general kinds of thin-film materials are mostly studied, either metallic cobalt alloys or insulating oxides. We are interested in the latter class of materials and in particular in gaining a basic material understanding of the crystallographically isomorphous spinel iron oxides, Fe 3 O 4 (magnetite) and gamma Fe 2 O 3 (maghemite). While the normal spinels have the bigger divalent metal atoms on the B sites and the trivalent atoms on the smaller A sites, Fe 3 O 4 is different in that it has iron atoms with two different valencies ( + 2 and + 3) randomly distributed at room temperature in the same kind of lattice sites, the octahedral B sites. This fact is responsible for its conductive character.' Gamma Fe 2 O 3 is a metastable ferrimagnetic oxide spinel with the same composition as the more stable hexagonal structure alpha Fe 2 O 3 phase that has antiferromagnetic properties. Gamma Fe 2 O 3 can only be obtained by having kinetics overrule thermodynamics. In other words, in order to obtain gamma, we have to further oxidize Fe 3 O 4 to increase the oxygen content while conserving the same spinel skeleton structure. In this new configuration the F e + 2 atoms will either oxidize to F e + 3 or move to another site leaving iron vacancies behind2 due to the fact that the former atoms have the lowest binding energy. Our experimental work is divided in two steps: first, the deposition process to obtain a film of Fe3O4, and then the postdeposition or annealing process that will enable this oxide under specific experimental conditions to oxidize to gamma Fe 2 O 3 . In the first part of the paper, we will discuss the
a>
Also at Magnetic Recording Institute.
344
J. Mater. Res. 3 (2), Mar/Apr 1988
http://journals.cambridge.org
results of the deposition process. A structural characterization is reported correlating the deposition parameters, substrate temperature, and oxygen flow with the optical and magnetic properties of the material. The second part will discuss the properties of the annealed oxides in relation to the postdeposition parameters as well as the initial deposition conditions.
II. EXPERIMENTAL Films of Fe 3 O 4 are obtained by reactive rf sputtering onto Si (100) substrates, in an S-gun magnetron deposition system (Varian). The substrates were placed on a planetary holder where the rotation speed was fixed at 60 rpm. The substrate temperature was monitored by a thermocouple located near the rear side of the holder. The film thickness was 1000 A. The target was iron doped with 0.75 at. % osmium in order to increase the coercivity of the samples. The sputtering gas was argon and the reactive gas was oxygen. The partial pressures of both gases were monitored before and during the deposition by an Inficon residual gas analyzer. Two mass flow transducers regulated the argon and oxygen flow rates, whereby the argon rate was always fixed at 80 seem (standard cubic cm). In th
Data Loading...
