Constrained Magnetic Vector Inversion of Scanning Magnetic Microscopy Data for Modelling Magnetization of Multidomain Mineral Grains

Author(s):  
Peter Lelièvre ◽  
Zeudia Pastore ◽  
Nathan Church ◽  
Madeline Lee ◽  
Hirokuni Oda ◽  
...  

<p>We are using 3D magnetic vector inversion (MVI) of scanning magnetic microscopy (SMM) data to investigate the fine‐scale magnetization of rock samples, and particularly of their remanence carriers, which can record geologically meaningful information. Previous investigations of magnetite grains suggest variable remanence intensities and directions coherent with multidomain behaviour. This research seeks to improve our understanding of the contribution of different microstructures on remanence acquisition.</p><p>SMM offers a spatial resolution down to tens of micrometers, allowing detailed investigation of discrete magnetic mineral grains, or magnetic textures and structures. However, all magnetic measurements are, at some scale, bulk measurements. Further analysis of the data is required to extract information about the magnetization within the samples: for this, we employ state-of-the-art MVI methods. The MVI problem suffers from a high degree of nonuniqueness. Additional constraints are required to obtain accurate, reliable and interpretable results. Such constraints are readily available for this application.</p><p>SMM instruments use magnetic shields or Helmholtz coils to allow collection of data in controlled magnetic fields, enabling the removal of induced magnetization effects. Measurements can be taken both above and below the sample. Individual magnetized mineral grains are easily outlined through optical and electron microscopy. The internal geometry of the oxide mineral phases and compositions can also be constrained. Physical property information constrains the range of magnetization intensity. As such, there is a tremendous amount of constraining information invaluable for reducing the nonuniqueness of the inverse problem. We use a highly flexible and functional inversion software package, MAGNUM, developed jointly at Mount Allison University and Memorial University of Newfoundland, that allows incorporation of all available constraints.</p><p>We take a multitiered approach for investigating specific magnetized grains. First, coarse regional inversions are performed to assess and remove any effects of other magnetized grains in the vicinity. The entire grain is then modelled with a homogeneous magnetization to obtain an approximate but representative bulk magnetization. The grain is then modelled as a collection of independent subdomains, each with a different homogeneous magnetization direction. Subsequently, more heterogeneous scenarios are considered by relaxing inversion constraints until the data can be fit to the desired degree.</p><p>Obtaining reliable information about the magnetic mineralogy of rock samples is vital for an understanding of the origin of rock bulk behaviour in both the laboratory and larger scale magnetic surveys. This work is among the first to simultaneously invert SMM data collected above and below a thin sample, which is critical for improving depth resolution on thicker samples. It is also the first time we have been able to incorporate all available constraints into inverse modelling to improve results.</p>

Geophysics ◽  
2020 ◽  
Vol 85 (3) ◽  
pp. J33-J49 ◽  
Author(s):  
Dominique Fournier ◽  
Lindsey J. Heagy ◽  
Douglas W. Oldenburg

Magnetic vector inversion (MVI) has received considerable attention over recent years for processing magnetic field data that are affected by remanent magnetization. However, the magnetization models obtained with current inversion algorithms are generally too smooth to be easily interpreted geologically. To address this, we have reviewed the MVI formulated in a spherical coordinate system. We tackle convergence issues posed by the nonlinear transformation from Cartesian to spherical coordinates by using an iterative sensitivity weighting approach and a scaling of the spherical parameters. The spherical formulation allows us to impose sparsity assumptions on the magnitude and direction of magnetization independently and, as a result, the inversion recovers simpler and more coherent magnetization orientations. The numerical implementation of our algorithm on large-scale problems is facilitated by discretizing the forward problem using tiled octree meshes. All of our results are generated using the open-source SimPEG software. We determine the enhanced capabilities of our algorithm on a large airborne magnetic survey collected over the Kevitsa Ni-Cu-platinum group elements (PGE) deposit. The recovered magnetization direction inside the ultramafic intrusion and in the host stratigraphy is consistent with laboratory measurements and provides evidence for tectonic deformation.


2021 ◽  
Vol 23 (1) ◽  
pp. 195-211
Author(s):  
I.M. Okiyi ◽  
S.I. Ibeneme ◽  
E.Y. Obiora ◽  
S.O. Onyekuru ◽  
A.I. Selemo ◽  
...  

Residual aeromagnetic data of parts of Southeastern Nigerian sedimentary basin were reduced to the equator and subjected to magnetic vector inversion and spectral analysis. Average depths of source ensembles from spectral analysis were used to compute depth to magnetic tops (Z), base of the magnetic layer (Curie Point t Depth (CPD)), and estimate geothermal gradient and heat flow required for the evaluation of the geothermal resources of the study area. Results from spectral analysis showed depths to the top of the magnetic source ranging between 0.45 km and 1.90 km; centroid depths of 4 km - 7.87 km and CPD of between 6.15 km and 14.19 km. The CPD were used to estimate geothermal gradients which ranged from 20.3°C/km to 50.0°C/km 2 2 and corresponding heat flow values of 34.9 mW/m to 105 mW/m , utilizing an average thermal conductivity -1 -1 of 2.15 Wm k . Ezzagu (Ogboji), Amanator-Isu, Azuinyaba, Nkalagu, Amagunze, Nta-Nselle, Nnam, Akorfornor environs are situated within regions of high geothermal gradients (>38°C/Km) with models delineated beneath these regions using 3D Magnetic Vector Inversion, having dominant NW-SE and NE-SW trends at shallow and greater depths of <1km to >7 km bsl. Based on VES and 2D imaging models the geothermal system in Alok can be classified as Hot Dry Rock (HDR) type, which may likely have emanated from fracture systems. There is prospect for the development of geothermal energy in the study area. Keywords: Airborne Magnetics, Magnetic Vector Inversion, Geothermal Gradient, Heat Flow, Curie Point Depth, Geothermal Energy.


Nanomaterials ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 752 ◽  
Author(s):  
Thomas Saerbeck ◽  
Henning Huckfeldt ◽  
Boris P. Toperverg ◽  
Arno Ehresmann

We present a detailed analysis of the in-plane magnetic vector configuration in head-to-head/tail-to-tail stripe domain patterns of nominal 5 μm width. The patterns have been created by He-ion bombardment induced magnetic patterning of a CoFe/IrMn3 exchange bias thin-film system. Quantitative information about the chemical and magnetic structure is obtained from polarized neutron reflectometry (PNR) and off-specular scattering (OSS). The technique provides information on the magnetic vector orientation and magnitude along the lateral coordinate of the sample, as well as the chemical and magnetic layer structure as a function of depth. Additional sensitivity to magnetic features is obtained through a neutron wave field resonance, which is fully accounted for in the presented analysis. The scattering reveals a domain width imbalance of 5.3 to 3.7 μm of virgin and bombarded stripes, respectively. Further, we report that the magnetization in the bombarded stripe significantly deviates from the head-to-head arrangement. A domain wall of 0.6 μm with homogeneous magnetization direction is found to separate the two neighboring domains. The results contain detailed information on length scales and magnetization vectors provided by PNR and OSS in absolute units. We illustrate the complementarity of the technique to microscopy techniques for obtaining a quantitative description of imprinted magnetic domain patterns and illustrate its applicability to different sample systems.


2013 ◽  
Vol 669 ◽  
pp. 46-50
Author(s):  
Y.N. Han ◽  
X.F. Han ◽  
H.L. Liu

The crystallographic structural characteristics and magnetic properties of Ho3Fe29-xTx (T=V and Cr) compounds have been investigated by using Rietveld refinement analysis of X-ray diffraction (XRD) pattern and magnetic measurements. The calculated results indicate that among the 11 different kinds of Fe sites in these Ho-Fe compounds the preferential sites of the stabilizing elements V and Cr are quite different. The refined lattice parameters of these compounds are in good agreement with the experimental data. Spin reorientations of easy magnetization direction (EMD) are observed at around 150 K for Ho3Fe27V2 and Ho3Fe25.5Cr3.5. At the around 1.7 T critical fields (HCR) first order magnetization process (FOMP) occurs in magnetization curves at 4.2 K for the magnetically aligned samples of Ho3Fe27V2 and Ho3Fe25.5Cr3.5.


2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Joseph M. Myre ◽  
Ioan Lascu ◽  
Eduardo A. Lima ◽  
Joshua M. Feinberg ◽  
Martin O. Saar ◽  
...  

1969 ◽  
Vol 20 ◽  
pp. 1-25
Author(s):  
M Ghisler ◽  
P.V Sharma

The chromite deposits of the Fiskenæsset region belong to a metamorphosed igneous complex of stratiform type occurring in the basement gneiss unit of older Precambrian age in West Greenland. Short descriptions and modal compositions of the different rock types are given together with the results of magnetic measurements on 60 rock samples (data shown in tables 1-5). On the basis of known geology and rock susceptibilities different models are discussed with respect to the applicability of both an airborne and a ground magnetometer survey. It is concluded that the susceptibility contrasts involved are sufficient for locating favourable host rocks by aeromagnetic survey, but direct magnetic prospecting for chromite horizons predominantly occurring within anorthosites may not be feasible.


2008 ◽  
Vol 8 (7) ◽  
pp. 3577-3581 ◽  
Author(s):  
C. Y. Liang ◽  
R. C. Che ◽  
H. X. Yang ◽  
J. Q. Li

Multi-crystalline La0.5Ba0.5MnO3 Nanowires have been synthesized with cationic surfactant at 220 °C. The structure, composition and physical property of the as-prepared nanowires have been characterized by a series of techniques including XRD, SEM, HRTEM, electron energy-loss spectroscopy (EELS) and magnetic measurements. It is found that the La0.5Ba0.5MnO3 nanowire has the typical cubic perovskite structure, each nanowire is composed of many small crystalline grains with different orientations. Valance state of manganese ion in La0.5Ba0.5MnO3 nanowires is determined by EELS technique. A "multi-nuclei" growth mode is proposed based on the microstructure analysis. The temperature dependence of magnetization has been briefly discussed.


2020 ◽  
Author(s):  
Suzanne McEnroe ◽  
Zeudia Pastore ◽  
Nathan Church ◽  
Falko Langenhorst ◽  
Hirokuni Oda

&lt;p&gt;Development in instrumentation and technology now allows for mapping of magnetic anomalies, caused by spatial variations in magnetization in the source materials, over a wide range of scales, from the millimeter mineral scale to the km crustal scale.&lt;/p&gt;&lt;p&gt;Traditional rock magnetic methods, used to investigate the magnetization in natural rock samples, are bulk measurements, which cannot be directly correlated to the individual mineral phases, or particles.&amp;#160; Scanning magnetic microscopy is a high-resolution mapping technique that allows for detailed investigation of the magnetization in natural rock samples. The technique generates a map of the magnetic field distribution over a planar surface of a rock sample with sub-millimeter resolution that can be used to correlate specific magnetic signals to the underlying mineralogy. This information is vital for an understanding of the origin of rock bulk behavior measured in both the laboratory, and in magnetic surveys.&lt;/p&gt;&lt;p&gt;Here we use 3D magnetic modeling to investigate the sources of the magnetic anomalies mapped over a sample thin section. The oxide grains in the thin sections are modeled using information from optical and electron microscopy (SEM and TEM) to constrain the source geometry, and with magnetic property data. The internal geometry of the oxide mineral phases (exsolution lamellae, intergrowths, symplectites) and compositions are constrained by EMP and TEM.&amp;#160;&lt;/p&gt;&lt;p&gt;Magnetic scans aid in locating the magnetic sources, and resolving the different magnetic components contributing to the bulk rock properties.&amp;#160; By modeling the small-scale variations in the oxides the direction and intensity of the magnetic grains are determined.&amp;#160; Aeromagnetic and ground magnetic data from the sample locations are used in conjunction with thin section magnetic mapping. Thin section results can be up-scaled to compare with ground and aeromagnetic data.&lt;/p&gt;


2011 ◽  
Vol 233-235 ◽  
pp. 1799-1802 ◽  
Author(s):  
Jian Jun Gu ◽  
Li Hu Liu ◽  
Yun Kai Qi ◽  
Qin Xu ◽  
Hui Yuan Sun

The spinel ferrite system Ni1-xMnxFe2O4 (x = 0.0, 0.25, 0.5, 0.75) nanowire arrays with an average diameter of about 80 nm, have been synthesized into nanopores of anodic aluminum oxide (AAO) template using the sol–gel technique. X-ray diffraction analysis shows the formation of single-phase nickel manganese ferrites. Scanning electron microscopy and transmission electron microscope images indicate that the nanowire arrays are composed of prolate spheroids with different crystal orientations. Magnetic measurements show that the saturation magnetization (Ms) of nickel ferrite nanowire arrays is lower than that of bulk ones. But the Ms of the samples doped with Mn are greater than that of bulk ones. We do not observe obviously easy magnetization direction of all nanowire arrays. The possible reasons that are responsible for the composition dependence of the properties are discussed.


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