Investigations of the structure and dynamics of materials have been an important and essential endeavor in condensed matter physics since the early 20th century. Both neutron and x‐ray scattering techniques have been used extensively to study the crystallographic structure of materials and provide complementary views of structure. For example, x‐ray diffraction has largely been applied to detailed crystallographic structure determination while neutron scattering has traditionally been the standard tool for studies of magnetic structure and the dynamics of condensed matter systems. The principle interaction that makes structure determination possible for x‐rays is the Coulomb interaction between x‐rays and the electronic distribution that gives rise to driven harmonic oscillation of the electrons, and the emission of electric dipole radiation. This is the classical Thomson scattering process. In addition to charge scattering, x‐rays interact with the magnetic moment of the system. When x‐ray energies are tuned through the absorption edges of an element of interest there is a resonant enhancement of the scattering signal now known as x‐ray resonant magnetic scattering. Away from the resonance condition, the magnetic scattering signal is known as nonresonant x‐ray magnetic scattering. In this article, we will concentrate mainly on the basic principles and applications of the x‐ray resonant magnetic scattering and nonresonant magnetic scattering.
<p>Paleomagnetic measurements provide very important methods to study the evolution of and variations in the Earth&#8217;s magnetic field throughout time. A vital tool used in paleomagnetism are natural magnetic minerals, such as the titanomagnetite (<em>TM</em>) solid solution series (Fe<sub>3-<em>x</em></sub>Ti<em><sub>x</sub></em>O<sub>4</sub>, 0 &#8804; <em>x</em> &#8804; 1). The main source of magnetic information in <em>TM</em>s is the thermal remanent magnetisation (<em>TRM</em>) they retain whilst being cooled below their Curie temperature (<em>T<sub>C</sub></em>) during their formation.</p><p>The key factor determining the <em>T<sub>C</sub>&#160; </em>is the composition. However, recent studies on natural and synthetic TM powders [1,2,3] have shown that their <em>T<sub>C</sub>&#160; </em>is also heavily influenced by their thermal history. Annealing various natural and synthetic <em>TM</em> powders at temperatures between 300&#176;C and 425&#176;C for timescales of hours to months resulted in changes in their <em>T<sub>C</sub>&#160; </em>of up to 150&#176;C.</p><p>The accuracy of many paleomagnetic measuring techniques, such as geomagnetic paleointensity estimates and paleomagnetic paleothermometry, depends on the exact knowledge of the Curie temperature. Changes in <em>T<sub>C</sub>&#160; </em>of such a considerable extend could deeply impact those techniques or even render them doubtable. So far, vacancy-mediated chemical clustering at the octahedral site of the <em>TM</em> structure has been postulated as the mechanism causing this phenomenon [2,3]. To further investigate the underlying processes, we synthesised a large (~6.5 mm diameter;&#160; ~27 mm length) <em>TM</em> single crystal using an optical floating zone furnace. Via SEM-EDX techniques it was established that the crystal was homogenous over its whole length with a composition of&#160; Fe<sub>2.64</sub>Ti<sub>0.36</sub>O<sub>4</sub>. Using a Physical Properties Measurement System (<em>PPMS</em>) the Curie temperatures of several pieces of the crystal were determined after different annealing treatments. For the first time it has been possible to detect systematic changes in <em>T<sub>C</sub>&#160; </em>with annealing in a <em>TM</em> single crystal.</p><p>Additionally within the scope of this project it was possible to determine the relationship between the extend of change in <em>T<sub>C</sub>&#160; </em>and the microstructure for polycrystalline samples.</p><p>&#160;</p><p>[1] Bowles, J. A., Jackson, M. J., Berqu&#243;, T. S., Solheid, P. A. and Gee, J. S. (2013), Nature Communications, 4, 1916. https://doi:10.1038/ncomms2938</p><p>[2] Jackson, M. J., and Bowles, J. A. (2018), J. Geophys. Res., 123, 1-20. https://doi:10.1002/2017JB015193</p><p>[3] Bowles, J. A., Lappe, S.&#8208;C. L. L., Jackson, M. J., Arenholz, E., & van der Laan, G. (2019). Geochem. Geophy. Geosy. 20. https://doi.org/10.1029/2019GC008217</p>
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