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<p>Paleomagnetic measurements provide very important methods to study the evolution of and variations in the Earth’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 ≤ <em>x</em> ≤ 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>  </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>  </em>is also heavily influenced by their thermal history. Annealing various natural and synthetic <em>TM</em> powders at temperatures between 300°C and 425°C for timescales of hours to months resulted in changes in their <em>T<sub>C</sub>  </em>of up to 150°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>  </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;  ~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  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>  </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>  </em>and the microstructure for polycrystalline samples.</p><p> </p><p>[1] Bowles, J. A., Jackson, M. J., Berquó, 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.‐C. L. L., Jackson, M. J., Arenholz, E., & van der Laan, G. (2019). Geochem. Geophy. Geosy. 20. https://doi.org/10.1029/2019GC008217</p>

Mo–Si–Ti alloys, like eutectic Mo–20Si–52.8Ti (at%), have previously been intensely investigated, owing to their excellent oxidation and creep resistance. To better understand high‐temperature mechanical behavior, a holistic assessment of microstructural features is necessary. Correspondingly, 3D‐focused ion beam tomography is carried out in Mo–20Si–52.8Ti. The results indicate a severely interconnected network of Mo solid solution (MoSS) and intermetallic (Ti,Mo)5Si3. Both phases retain similar network connectivity, lamellar sizes, etc. The brittle to ductile transition temperature (BDTT) is then determined through a series of bending tests and interpreted using the microstructural information. The BDTT is found to be ≈1100–1150 °C, different from Mo–9Si–8B with a continuous MoSS network. The BDTT is an immediate consequence of the continuous network of both MoSS and (Ti,Mo)5Si3. The MoSS network is instrumental in crack trapping and bridging, indicating that the present phase distribution maximized the mechanical performance over (Ti,Mo)5Si3. Having determined the network microstructure and BDTT, tensile creep behavior is evaluated and compared to previously published compressive creep results. The results show consistency in terms of strain rate, stress exponent, and microstructural features indicating a reliably good creep resistance for the network microstructure of Mo–20Si–52.8Ti regardless of loading direction.