日本物理学会九州支部特別講演会
題目：Crystalinity and stability of single/bi-layer epitaxial Fe3O4 thin films
講師：Prof. N.-T.H. Kim-Ngan (Pedagogical University)
日時：2019 年 5 月 13 日(月) 14:00～15:00
場所：九州大学伊都キャンパス ウエスト 1 号館 A-711(理学部物理学科会議室)
主催：日本物理学会九州支部
Abstract
Magnetite (Fe3O4) is one of the most known magnetic materials. Due to its fascinating properties andespecially its wide application as recording media and in catalyst, it has attracted a large attention since
1960s. Recently, due to the fact that Fe3O4 is referred as a half-metallic material having a full spinpolarization at the Fermi level and has a high critical temperature, it is considered as a promising candidate
for technical applications as spintronic devices at room temperature.
Spintronic devices are based on a thin film technology and thus it is highly required to obtain thinfilms with a high crystalline quality (crystallinity) and controllable physical properties. The difficulty inusing magnetite thin films is that their properties are strongly dependent on the layer properties as well ason the interaction between the layers and the substrates. Thus, it is very important to have a deep
understanding of not only the surface as well as the entire film properties but also the influence of different
processes at the interfaces of the magnetite films on those properties.
We focus on investigating the crystalinity and stability of the single and bi-layer films grown
epitaxially on MgO(001) substrates (Fe3O4/MgO(001), Fe3O4/Fe/MgO(001), Fe/Fe3O4/MgO(001)) withdifferent layer thickness in the range of 10-100nm. The influence of interdiffusion during the film-growthand of external conditions (e.g. ageing, thermal annealing, and 1MeV Ar+, Kr+ and Au+ ion irradiation)on the film crystalinity, on the layer structure and composition have been thoroughly studied by means of
Rutherford backscattering spectrometry (RBS), channeling experiments (RBS-C) and X-ray reflectometry(XRR). TRIM/SRIM SIMNRA computer code were used for data estimation and analysis.
The single-layer has always a good crystalinity. However, a pure magnetite layer could be found on
the surface of singler-layer film in the case if the layer thickness is larger than 20 nm. In the case of bilayer films, independently on the layer thickness, on the film surface is always the stoichiometric Fe3O4layer. However, their crystalinity is lower.
Thermal annealing promotes Mg out-diffusion and consequently the surface layer composition change
into a spinel one.
The magnetite composition in the single-layer films was easily modified even if upon ion irradiations
by small ions fluence.
The important outcome is our finding the high stability of the surface Fe3O4 layer of the bi-layer film
upon ion irradiations. For all bi-layer films, the stoichiometric Fe3O4 layer on the film surface is wellpreserved at a quite high rare-gas (Ar+ and Kr+) ion as well as upon metallic (Au+) ion irradiations, despiteof some decreasing in the layer thickness, strong intermixing at the interfaces and a partial or complete
oxidization of the buffer Fe layer.
The research has been realized within the scope of cooperation between NanoLab-UP Krakow (author,M. Krupska, S. Sowa. A. Duda) and other research groups in Krakow (led by J. Korecki), FrankfurtDamstadt (A.G. Balogh) and in Prague (A. Mackova, P. Malinsky).
連絡先: 九州大学大学院理学研究院物理学部門 和田 裕文
E-mail: wada@phys.kyushu-u.ac.jp