Ferromagnetic Resonance of Interacting Particles: A Theoretical Study

North Carolina State University, Raleigh NC

Investigators

Abstract

Magnetotactic bacteria are a taxonomically diverse group of bacteria that have chains of ferromagnetic crystals inside. These bacteria mostly live in the oxic-anoxic interface (OAI) of aquatic environments. The magnetic chains orient the bacteria parallel to the Earth's magnetic field and help them to maintain their position near the OAI. These chains show the fingerprint of natural selection acting to optimize the magnetic moment per unit iron. This is achieved in a number of ways: the alignment in chains, a narrow size range, crystallographic perfection and chemical purity. Because of these distinctive characteristics, the particles can still be identified after the bacteria have died. Such magnetofossils are useful both as records of bacterial evolution and environmental markers. They can most reliably be identified by microscopy, but that is very labor-intensive. A number of magnetic measurements have been developed to identify magnetofossils quickly and non-invasively. However, the only test that can specifically identify the chain structure is ferromagnetic resonance (FMR), which measures the response to a magnetic field oscillating at microwave frequencies. No theory has been developed to predict the FMR spectra for chains of magnetic particles. The goal of this project is to develop such a theory. The objectives of the proposed work are as follows: 1. To calculate the signature of particle interactions on FMR spectra of magnetosome chains, 2. To determine the effects on FMR spectra of chain disruption and oxidation, 3. To explore possible enhancements of the current FMR methods, and 4. To create resources for analyzing FMR spectra. This project is supported by the Geophysics and Geobiology & Low Temperature Geochemistry Programs and the Office of Cyberinfrastructure's CI-Reuse Venture Fund.