Version du 21 avril 2015 à 10:24

Introduction :
L’intention est d’offrir une compréhension des liens intimes qui existent entre la chimie et le magnétisme des minéraux composant les roches terrestres et celles de notre univers. Les notions transmises verront une utilité et une complémentarité dans diverses domaines de recherche des doctorants de l’ED560, que se soit la géochimie des enveloppes externes, des eaux, ou des enveloppes internes de la terre ou la géophysique expérimentale, en plus des domaines évidents que sont le paléomagnétisme, le géomagnétisme ou encore la tectonique et la volcanologie.
This course will be taught in English.

Ce cours est programmé dans le cadre des cours scientifiques de l'EDSTEP'UP est financé par l'accord cadre entre l’IPGP et l’University of Minnesota – Twin Cities.

Description :

The term Magnetochemistry was popular in the middle part of the 20th century when physical chemistry became a strong influence on magnetic study of ionic compounds. In rock magnetism the more recent trend has been to treat magnetic oxides as ‘black boxes’ whose properties are mainly influenced by size, internal spin structure and inter-particle interactions.

The present short course will be structured in four parts where one objective may be treated as a corrective to this prevailing view.

The first part will focus on Fe ions in spinel and trigonal crystal lattices and work progressively through the topics of their ionic or ‘Goldschmidt size’, the origin of their magnetic moments, the spin-orbit coupling and the effect of local structure and crystal field (meaning electric field from non-cubic local oxygen structure). The focus on Fe ions will end with familiarity of the site preferences of common ions in iron oxides, pure and substituted with transition metal ions such as aluminium, chromium, titanium.

In the second part we consider compositions of the most relevant iron oxides and their characteristic properties such as saturation magnetization, crystalline anisotropy, Curie and Néel points. The replacement by diamagnetic and paramagnetic ions resulting in changes in these properties will also be explored. We will briefly discuss the techniques for measuring these parameters and their magnetic field and temperature dependences. Finally, we will familiarize ourselves with the common solid solutions of found in nature. In the third part, our focus will be on cation distribution and types of analyses (magnetic and non-magnetic) that yield cation distributions. Such techniques may include low temperature magnetization, X-ray diffraction, neutron diffraction, Mössbauer spectroscopy and X-ray magnetic circular dichroism (XMCD). The fourth and final part will examine how the knowledge above can and does help us answer geological and geochemical questions. This will be achieved by choosing selected journal articles from various systems of interest reflecting the diverse research interest of the participants. We will also point to important unsolved problems that are worthy of future research. Examples of pertinent research areas are:

    •	Examples of pertinent research areas are:

o Paleoclimate and paleoenvironmental studies from sedimentary archives (continental, marine, lacustrine, …)
o Biomineralization
o Iron oxides in igneous systems (volcanism, alteration of the oceanic crust,…)
o Meteorites (e.g. carbonaceous chondrites)
o Anthropogenic pollution (airborne particle, fluvial contaminants, soil remediation,…)
o Mineral Physics (mantle and crustal spinels,…)

Inscription :
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