Quantitative Vectorial Magnetic Imaging of Multi-Domain Rock Forming Minerals Using Nitrogen-Vacancy Centers in Diamond

Abstract

Magnetization in rock samples is crucial for paleomagnetometry research, as it harbors valuable geological information on long term processes, such as tectonic movements and the formation of oceans and continents. Nevertheless, current techniques are limited in their ability to measure high spatial resolution and high-sensitivity quantitative vectorial magnetic signatures from individual minerals and micrometer scale samples. As a result, our understanding of bulk rock magnetization is limited, specifically for the case of multi-domain minerals. In this work we use a newly developed nitrogen-vacancy magnetic microscope, capable of quantitative vectorial magnetic imaging with optical resolution. We demonstrate direct imaging of the vectorial magnetic field of a single, multi-domain dendritic magnetite, as well as the measurement and calculation of the weak magnetic moments of an individual grain on the micron scale. These results pave the way for future applications in paleomagnetometry, and for the fundamental understanding of magnetization in multi-domain samples.When igneous rocks in Earth's crust are formed by cooling of hot magma they acquire thermoremanent magnetization (TRM) parallel and proportional to the ambient field at the time of cooling. TRM can remain stable for millions of years preserving valuable geological magnetic information on complex long term processes, such as plate tectonic movements and formations of oceans and continents [1]. Despite its importance, little is known on the details of how thermoremanent magnetic information is acquired and retained in rocks [2]. Paleomagnetism, the science of studying natural magnetic information, heavily relies on Néel theory [3] of single-domain (SD) minerals. Yet, the dimensions of rock-forming minerals typically exceed the sub-micrometric threshold size for SD. As such, TRM is mostly held by multi-domain (MD) particles rather than by SD. In the absence of a general analytical formulation for TRM in MD, there is a growing need for direct observations of natural MD magnetization. Particularly, vectorial imaging of magnetic fields generated by MD particles with sub-micron spatial resolution and micrometer scale sample-detector distance, along with high sensitivity (µT / √ Hz), is critical for understanding the mechanism controlling the geometry and size of MD arrangements, the total moment exerted by individual natural crystals, and the stability of MD magnetic information over geological times.There are a number of magnetic imaging techniques that have been used in paleomagnetic research in a complementary fashion: Kerr effect [4] , Magnetic Force Microscopy (MFM) [5], electron holography [6], and SQUID microscopy [7]. Recently, a newly developed method based on nitrogen-vacancy (NV) magnetic microscopy [8][9][10], has been demonstrated by [11,12] in the context of paleomagnetometry. NV magnetic microscopy enables direct measurements of the three components of the magnetic field vector at a constant height above the sample in a room temperature environ...

Sensitivity optimization for NV-diamond magnetometry

“…NV − centers have also been employed for high-sensitivity imaging of temperature (Kucsko et al, 2013), strain, and electric fields (Dolde et al, 2011;Barson et al, 2017). Recent examples of ensemble-NV − sensing applications include magnetic detection of single-neuron action potentials (Barry et al, 2016); magnetic imaging of living cells (Le Steinert et al, 2013), malarial hemozoin (Fescenko et al, 2019), and biological tissue with subcellular resolution (Davis et al, 2018); nanoscale thermometry (Kucsko et al, 2013;Neumann et al, 2013); single protein detection (Shi et al, 2015;Lovchinsky et al, 2016); nanoscale and micron-scale NMR (Staudacher et al, 2013;Loretz et al, 2014;DeVience et al, 2015;Rugar et al, 2015;Kehayias et al, 2017;Bucher et al, 2018;Glenn et al, 2018); and studies of meteorite composition (Fu et al, 2014) and paleomagnetism (Farchi et al, 2017;Glenn et al, 2017).…”

Determining Individual Particle Magnetizations in Assemblages of Micrograins

“…Many studies have employed high‐end magnetometry techniques to go beyond the traditional bulk rock measurements to unravel the magnetic state of Earth materials and meteorites or to progress our fundamental knowledge of micromagnetic processes in MD grains. Recent examples are electron holography (Almeida et al, ), scanning superconducting quantum interference device microscopy (SSM) (Lima & Weiss, ; Weiss et al, ), magnetic tunnel junction scanners (Lima et al, ), X‐ray photoemission electron microscopy (Nichols et al, ), and quantum diamond microscopes (Farchi et al, ; Glenn et al, ). Some of these studies tried to avoid the adverse contribution of bad paleomagnetic recorders by selecting the most suitable materials or the best regions in a sample, but none attempted to obtain magnetic information for individual magnetic grains.…”

Principles and techniques of the quantum diamond microscope

“…Followup work with the QDMs have demonstrated their utility in imaging magnetization carriers at the grain scale. Recent example applications have included the imaging of large magnetite grains to visualize multi-domain structure [104] and of zircons [117][118][119] to understand and constrain the history of Earth's dynamo. The full potential of the QDM as a rock magnetic instrument are only beginning to be explored, with ongoing experiments on terrestrial and extraterrestrial rock types being pursued.…”