[1] We present a comparative study of nonheating paleointensity methods, with the aim of determining the optimum method for obtaining paleointensities from ''dusty olivine'' in chondritic meteorites. The REM method, whereby thermoremanent magnetization (TRM) is normalized by saturation isothermal remanent magnetization (SIRM), is shown to ''over normalize'' TRM in dusty olivine due to the transformation of stable single-vortex (SV) states to metastable single-domain (SD) states in a saturating field. The problem of over normalization is reduced in the REMc and REM' methods, which more effectively isolate the high-coercivity stable SD component of remanence. A calibration factor of f ¼ 1600 (1000 < f < 2900) is derived for the REM' method. Anhysteric remanent magnetization (ARM) is shown to be a near perfect analogue of TRM in the stable SD component of dusty olivine. ARM normalization of the high-coercivity (100-150 mT) remanence with a calibration factor f ARM ¼ 0.91 (0.7 < f ARM < 1.2) yields paleofield estimates within 6 30% of the actual field values for SD dominated samples. A Preisach method for simulating TRM acquisition using information extracted from first-order reversal curve (FORC) diagrams is shown to work well for SD dominated samples, but fails when there is a large proportion of SV remanence carriers. The failure occurs because (1) SV states are not properly incorporated into the Preisach distribution of remanence carriers, and (2) the acquisition of TRM by SV states is not properly modeled by the underlying SD thermal relaxation theory.

The elastic and anelastic properties of three different samples of Fe(x)O have been determined in the frequency range 0.1-2 MHz by resonant ultrasound spectroscopy and in the range 0.1-50 Hz by dynamic mechanical analysis in order to characterize ferroelastic aspects of the magnetic ordering transition at T(N) ~ 195 K. No evidence was found of separate structural and magnetic transitions but softening of the shear modulus was consistent with the involvement of bilinear coupling, λe(4)q, between a symmetry-breaking strain, e(4), and a structural order parameter, q. Unlike a purely ferroelastic transition, however, C(44) does not go to zero at the critical temperature, T*(c), due to the intervention of the magnetic ordering at a higher temperature. The overall pattern of behaviour is nevertheless consistent with what would be expected for a system with separate structural and magnetic instabilities, linear-quadratic coupling between the structural (q) and magnetic (m) driving order parameters, λqm(2), and T(N) > T*(c). Comparison with data from the literature appears to confirm the same pattern in MnO and NiO, with a smaller difference between T(N) and T*(c) in the former and a larger difference in the latter. Strong attenuation of acoustic resonances at high frequencies and a familiar pattern of attenuation at low frequencies suggest that twin walls in the rhombohedral phase have typical ferroelastic properties. Acoustic dissipation in the stability field of the cubic phase is tentatively attributed to anelastic relaxations of the defect ordered structure of non-stoichiometric wüstite or of the interface between local regions of wüstite and magnetite, with a rate controlling step determined by the diffusion of iron.

&lt;p&gt;Paleomagnetic measurements provide very important methods to study the evolution of and variations in the Earth&amp;#8217;s magnetic field throughout time. A vital tool used in paleomagnetism are natural magnetic minerals, such as the titanomagnetite (&lt;em&gt;TM&lt;/em&gt;) solid solution series (Fe&lt;sub&gt;3-&lt;em&gt;x&lt;/em&gt;&lt;/sub&gt;Ti&lt;em&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/em&gt;O&lt;sub&gt;4&lt;/sub&gt;, 0 &amp;#8804; &lt;em&gt;x&lt;/em&gt; &amp;#8804; 1). The main source of magnetic information in &lt;em&gt;TM&lt;/em&gt;s is the thermal remanent magnetisation (&lt;em&gt;TRM&lt;/em&gt;) they retain whilst being cooled below their Curie temperature (&lt;em&gt;T&lt;sub&gt;C&lt;/sub&gt;&lt;/em&gt;) during their formation.&lt;/p&gt;&lt;p&gt;The key factor determining the &lt;em&gt;T&lt;sub&gt;C&lt;/sub&gt;&amp;#160; &lt;/em&gt;is the composition. However, recent studies on natural and synthetic TM powders [1,2,3] have shown that their &lt;em&gt;T&lt;sub&gt;C&lt;/sub&gt;&amp;#160; &lt;/em&gt;is also heavily influenced by their thermal history. Annealing various natural and synthetic &lt;em&gt;TM&lt;/em&gt; powders at temperatures between 300&amp;#176;C and 425&amp;#176;C for timescales of hours to months resulted in changes in their &lt;em&gt;T&lt;sub&gt;C&lt;/sub&gt;&amp;#160; &lt;/em&gt;of up to 150&amp;#176;C.&lt;/p&gt;&lt;p&gt;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 &lt;em&gt;T&lt;sub&gt;C&lt;/sub&gt;&amp;#160; &lt;/em&gt;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 &lt;em&gt;TM&lt;/em&gt; 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;&amp;#160; ~27 mm length) &lt;em&gt;TM&lt;/em&gt; 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&amp;#160; Fe&lt;sub&gt;2.64&lt;/sub&gt;Ti&lt;sub&gt;0.36&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;. Using a Physical Properties Measurement System (&lt;em&gt;PPMS&lt;/em&gt;) 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 &lt;em&gt;T&lt;sub&gt;C&lt;/sub&gt;&amp;#160; &lt;/em&gt;with annealing in a &lt;em&gt;TM&lt;/em&gt; single crystal.&lt;/p&gt;&lt;p&gt;Additionally within the scope of this project it was possible to determine the relationship between the extend of change in &lt;em&gt;T&lt;sub&gt;C&lt;/sub&gt;&amp;#160; &lt;/em&gt;and the microstructure for polycrystalline samples.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[1] Bowles, J. A., Jackson, M. J., Berqu&amp;#243;, T. S., Solheid, P. A. and Gee, J. S. (2013), Nature Communications, 4, 1916. https://doi:10.1038/ncomms2938&lt;/p&gt;&lt;p&gt;[2] Jackson, M. J., and Bowles, J. A. (2018), J. Geophys. Res., 123, 1-20. https://doi:10.1002/2017JB015193&lt;/p&gt;&lt;p&gt;[3] Bowles, J. A., Lappe, S.&amp;#8208;C. L. L., Jackson, M. J., Arenholz, E., &amp; van der Laan, G. (2019). Geochem. Geophy. Geosy. 20. https://doi.org/10.1029/2019GC008217&lt;/p&gt;