Towards a Model System for Lamellar Magnetism by Atomic Layer Deposition

Abstract

We have developed the first atomic layer deposition (ALD) processes for thin films of iron in a +2 oxidation state (Fe2+), as well as nickel titanate (NiTiO3). These materials are important for the understanding and realization of exotic magnetic properties useful in computer technology. Pushing modern computer technology forward requires insight into more complex materials than bar magnets. With a constant drive towards making devices smaller, producing components in the form of thin films is often the solutions. However, before utilizing desirable properties, they must be understood in order to make the required materials in a controlled manner. An example of materials with interesting magnetic properties are naturally formed rocks from Modum, Norway. They consist of two different minerals, namely hematite (Fe2O3) and ilmenite (FeTiO3). These compounds are quite uninteresting separately, but show fascinating and sought-after magnetic properties when combined. These unique features arise from super-thin alternating layers, with thicknesses down to 1 nanometer. ALD is a technique for making ultra-thin films, much like the layers in the rocks from Modum. The problem is making FeTiO3, which contains iron (Fe) in a +2 oxidation state. Iron is easily oxidized to +3, which is the oxidation state it has in Fe2O3. We have developed the first ALD process to directly deposit thin films with only Fe2+. We then used this process to make FeTiO3. However, the films also contained unwanted substances, and could not be used in combination with Fe2O3. To learn more about the properties of the Modum rocks, another approach was chosen: swapping iron for nickel (Ni), as nickel is easier to keep in oxidation state +2 than iron. This was used in combination with Fe2O3 to create thin, alternating layers with NiTiO3, just as in the rocks from Modum. The magnetic properties of the samples were investigated, and though some interesting features were observed, a full understanding of their origin remains a mystery.