Visualized effect of oxidation on magnetic recording fidelity in pseudo-single-domain magnetite particles

Abstract

Magnetite (Fe3O4) is an important magnetic mineral to Earth scientists, as it carries the dominant magnetic signature in rocks, and the understanding of its magnetic recording fidelity provides a critical tool in the field of palaeomagnetism. However, reliable interpretation of the recording fidelity of Fe3O4 particles is greatly diminished over time by progressive oxidation to less magnetic iron oxides, such as maghemite (γ-Fe2O3), with consequent alteration of remanent magnetization potentially having important geological significance. Here we use the complementary techniques of environmental transmission electron microscopy and off-axis electron holography to induce and visualize the effects of oxidation on the magnetization of individual nanoscale Fe3O4 particles as they transform towards γ-Fe2O3. Magnetic induction maps demonstrate a change in both strength and direction of remanent magnetization within Fe3O4 particles in the size range dominant in rocks, confirming that oxidation can modify the original stored magnetic information.

On the ‘centre of gravity’ method for measuring the composition of magnetite/maghemite mixtures, or the stoichiometry of magnetite-maghemite solid solutions, via57Fe Mössbauer spectroscopy

“…It is a natural parameter to measure with Mössbauer spectroscopy in these samples, given that Mössbauer is an atom-based experimental technique, wherein, to a good approximation, every Fe atom contributes an equally-weighted absorption signal 6 . In the case of a magnetite/maghemite mixture, when expressed as a percentage, α may be considered to be the atomic percentage (at.%) of Fe atoms present in the form of magnetite in the mixture:…”

“…Indeed, magnetite is the most magnetic of all the naturally occurring oxides on Earth, having a room temperature saturation magnetisation by mass of M s = 92 Am 2 kg −1 , while maghemite is also strongly magnetic, with M s = 76 Am 2 kg −1 at room temperature [2]. These phases play a significant role in geomagnetism and palaeomagnetism [3][4][5][6], and are also important markers in archaeomagnetism, largely due to their presence in clays and clay products such as pottery [7][8][9]. Maghemite is an oxidation product of magnetite, and as such the interplay and balance between the two phases is often informative, both in centuries-old samples [10] and in more contemporary materials, such as the corrosion products of carbon steels [11][12][13].…”

Multiscale differential phase contrast analysis with a unitary detector

“…Such characterization is also of paramount importance for biomedical applications like hyperthermia treatment or local drug delivery [12,13]. Other examples are paleomagnetism, environmental magnetism or biomagnetism [14][15][16][17].…”

Mapping the magnetic and crystal structure in cobalt nanowires

“…[22][23][24][25][26][27] In this matter, TEM offers the possibility to combine specialized techniques to investigate structure-property relationships at scales ranging from a few microns to a few nanometers. [28][29][30][31][32][33] For instance, off-axis electron holography affords the study of the magnetization distribution inside nanostructures in a detailed manner, while the coupling of nano-probe scanning and precession electron diffraction is a powerful technique developed to automatically obtain crystallographic orientation/phase maps of nanosized polycrystalline structures. 34 Precession electron diffraction (PED) is a technique that collects electron diffraction patterns under a conical oscillation of the electron beam leading in a significant reduction of the dynamical effects due to the thickness of the sample.…”