Nanoparticle Magnetic Characterization and Comparison of Rock Anisotropy Methods

  • Author / Creator
    Snow, Brendan
  • The mass susceptibility and associated Curie temperatures were determined for a series of ternary manganese and zinc ferrite nanoparticles (Mn–Zn ferrite NPs) with ratios of Mn:Zn ranging from 0.67-2.33. Variations in the Mn:Zn ratio of these Mn–Zn ferrite nanoparticles largely unaffected the particle size with the average grain diameter for the samples studied being 7nm. At room temperature (20°C) and low applied field strength the mass susceptibility remains relatively consistent as the Mn:Zn ratio increases from 0.67 to 2.33 with the further increase in the amount of manganese resulting in a slight decrease of the mass susceptibility. A similar trend is also observed in the saturation magnetization for each particle, where the saturation magnetization decreases slightly with increased Mn content. At elevated temperatures (125°C) both the saturation magnetization and magnetic susceptibility increase with the relative Mn content, both at a relatively similar ratio of 5x stronger magnetization saturation and susceptibility for a ratio of 2.33 than 0.67. Mn rich compositions have a significantly lower temperature dependence which makes them more suitable for downhole conditions of over 100°C with a response greater than 6.5 times that of nanomagnetite (nMag). The correlations between anisotropy of magnetic susceptibility (AMS), anisotropy of isothermal remanent magnetization (AIRM), gyroremanent magnetization (GRM) and acoustic anisotropy were investigated for a set of metasediments and metavolcanics and plutonic rocks from a ductile shear zone in the Flin Flon Belt of the Trans-Hudson Orogen. Ultrasonic laboratory measurements of shear wave velocities were carried out at various polarizations under atmospheric pressure conditions to characterize shear wave anisotropy and verify alignment to visible textural elements within the rock sample. The fastest shear wave velocities observed systematically had a polarization within the bedding plane and parallel to any visible lineation while the slowest shear wave propagation direction was found to be perpendicular to the bedding plane. These results were then compared to various magnetic fabric measurement techniques where the anisotropy of magnetic susceptibility was compared to the anisotropy of isothermal remanent magnetization and gyroremanent magnetization. Comparisons between these different magnetic methods determined that there was a clear foliation visible in the magnetic fabric with the bulk of the fabric being sourced from the diamagnetic to paramagnetic components which aligned with the lattice preferred orientation (LPO) observed via acoustic anisotropy. Some samples included a ferrimagnetic component largely due to multidomain ferrimagnetic grains. One sample was observed to contain stable single domain grains due to the retention of a GRM. This sample was shown to have a clear foliation in the XY plane which agreed with the visible fabric. This sample was originally thought to be quasi isotropic based on p-wave measurements however this is not the case due to the magnetic and s-wave anisotropies supporting a magnetic and acoustic rock fabric. The observed AMS and AIRM principle axes displayed a high degree of correlation with the elastic coefficients previously measured for each sample by Cholach et al. (2005). The orientation of s-wave splitting was also well aligned with the declination of the AMS principle axes with the maximum magnetic susceptibility axis having a similar declination to the azimuth of the fast polarity. The minimum principle magnetic susceptibility axis was aligned with the azimuth of the slow s-wave polarity.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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