ABSTRACT
When a ferrimagnetic or ferromagnetic material is placed in a static magnetic bias field it absorbs electromagnetic radiation. The frequency at which this absorption occurs depends on the material and the bias field strength. This phenomenon is known as ferromagnetic resonance (FMR) and is the electron analogue of nuclear magnetic resonance (NMR), the principle behind MRI machines (refer to Blakemore (1985) and Soohoo (1985) for a more detailed description). In the early stages of corrosion, the initial iron oxides formed are lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) which at room temperature are paramagnetic and antiferromagnetic, respectively (Cornell & Schwertmann 2003). Over time, ferrimagnetic magnetite (Fe3O4), and to a lesser extent maghemite (γ-Fe2O3) and weakly paramagnetic haematite (α-Fe2O3) are formed. All the corrosion products exhibit, to a greater or lesser extent, FMR behavior.
