NANOPARTICLES IN METERORITES: THE CONTRIBUTION OF SURFACES TO THE MAGNETIC CURIE TEMPERATURE AND MAGNETIC RECORDING FIDELITY

Lead Research Organisation: Imperial College London
Department Name: Earth Science and Engineering

Abstract

In meteoritic magnetism, the Curie temperature (the mineral dependent ferromagnetic ordering temperature) is routinely measured to identify magnetic mineralogy. The Curie temperature marks the break in a short-range nearest-neighbour ordering energy called the exchange energy, which causes the magnetic moments of atoms to align with each other in ferromagnetic materials. For crystals larger than 10-20 nm in size, the effect of atoms on the surface of a crystal that have fewer nearest neighbour atoms is relatively unimportant. However, for magnetic minerals less than 10 nm, the reduction in the number of nearest neighbour atoms leads to a reduction in the Curie temperature. To determine this effect we numerically solve the Hamiltonian describing the exchange interaction between atomic spins and their interaction with an external field (Figure 1). Variations in the exchange energy should theoretically also affect the recording fidelity of small particles; this is some that we wish to investigate. Starting with an existing three-dimensional numerical algorithm written for metallic iron, the project will develop the code for magnetite and other minerals of geological interest, for realistic three-dimensional geometries. Previous published calculations have only been for one-dimensional systems.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
ST/N504312/1 30/09/2015 29/09/2021
1665128 Studentship ST/N504312/1 30/09/2015 29/09/2019 Charles John PENNY
 
Description Density functional theory calculations of exchange energies in magnetite using Wien2k 
Organisation Vienna University of Technology
Country Austria 
Sector Academic/University 
PI Contribution Provided the initial idea of the problem to be tackled. Set-up and running calculations, data analysis, direction of project. Use of High Performance Computing services at Imperial College.
Collaborator Contribution Provided training in Vienna of the software package Wien2k in March 2017. Continue to provide expertise in overcoming persistent problems arising from the software.
Impact This work is a collaboration between the fields of Earth Science and Theoretical/Materials Chemistry.
Start Year 2017