Hiroshi Maeda1, Masayuki Hijikata1, Shigeru Kitahara1 and Ichiro Morimoto1
1National Research Institute for Metals, Tokyo
Plasma jet spray deposition was applied to the preparation of a few spinel type ferrite films, such as Mn-Zn, Mg-Zn, Mn-Mg ferrite, on alumina substrates. The optimum deposition conditions were studied under which the films as deposited agree with bulk material in properties, and were also studied on the diciding microsturctural factor affecting magnetic properties of the films. The results obtained are summarized as follows.
The properties of films depend largely on the substrate temperature during deposition and little on the spraying conditions such as the operating current, the deposition period, and the distance between a plasma jet torch nozzle and substrate. In the films deposited on a non-heated substrate, a large amount of a W\"ustite structure phase ((Fe~Mg)O,~FeO) exists, and so the saturation magnetization is considerably smaller than bulk values. Annealing in oxygen atmosphere at 900°C results in a perfect recovery from both these structural and magnetic faults. While coercive force, HC, decreases rapidly to about 20 Oe, as the annealing temperature rises above 900°C.
On the other hand, in the films deposited on a heated substrate, HC decreases almost linearly with rise in substrate temperature and reaches a value of 1.5 Oe above 1200°C, which is much small compared with that in the case of annealing. Therefore, it is advisable to heat the substrate at about 1200°C in order to get almost the same magnetic properties of the film as deposited as those of bulk materials.
The roughness of film surface also shows the same tendency as HC. No difference between films and bulk materials is recognized in the other microstructural properties. Namely, the diciding microstructural factor affecting the magnetic properties is smoothness of the film surface which is achieved only by heating substrates during deposition.
In the case of ferrite including zinc, a large amount of zinc content volatilizes during deposition.
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