Hydrostatic pressure effect on magnetic hysteresis parameters of pseudo‐single‐domain magnetite

Abstract

This paper reports the first in situ magnetic hysteresis measurements of pseudo‐single‐domain (PSD) magnetite under high pressure up to 1 GPa. The magnetic hysteresis measurements of stoichiometric PSD magnetite samples under hydrostatic pressure were carried out using a piston‐cylinder high‐pressure cell, and the pressure dependence of the hysteresis parameters of PSD magnetite was calculated from the hysteresis curves. It was found that coercivity (Bc) increases with increasing pressure as a quadratic function up to 1 GPa by ∼90%, which is different from the pressure dependences of Bc of multidomain and single‐domain magnetites. Coercivity of remanence also increases as a quadratic function, and saturation remanence (Mrs) increases with pressure up to 0.5 GPa by ∼20% until reaching saturation. In contrast, saturation magnetization is constant up to 1 GPa. The approximate demagnetizing factor calculated from the ratio Bc/Mrs increases with increasing pressure, suggesting that the number of lamellar domains increases with increasing pressure. The number of lamellar domains and domain wall width are theoretically estimated to increase under high pressure due to the changes in magnetostriction, elastic, and magnetocrystalline anisotropy constants, and these changes in magnetic domain structure should relate to the changes in the magnetic properties of PSD magnetite.

Rutile (U‐Th)/He Thermochronology: Temperature Sensitivity and Radiation Damage Effects

“…These results suggest that degassing with higher laser powers (≥10 A) induces U and Th loss through volatilization, causing the daughter to parent ratio to be artificially high and the dates to be artificially old. Parent isotope volatilization at higher laser power is consistent with previous observations in hematite (e.g., Hofmann et al, 2018) and perovskite (Stanley & Flowers, 2016), as well as apatite and titanite (if the latter two minerals are lased bare, not in a metal packet; House et al, 2000;Reiners & Farley, 1999).…”

“…overlapping ZHe dates of 89-97 Ma (Stanley & Flowers, 2016) and mostly older than AHe dates of 76 ± 10 Ma . BSE and EDS data reveal an~8-μm-thick titanite overgrowth on one of the two imaged crystals ( Figure S2d).…”

“…Ma from perovskite U-Pb (Griffin et al, 2014), and AHe dates of 43-73 Ma (Stanley, 2015). The Letseng kimberlite (sample SA12-24A) has a zircon U-Pb date of 94.6 ± 2 Ma (Allsopp et al, 1989), ZHe dates of 89-97 Ma (Stanley & Flowers, 2016), and mean AHe date of 75.8 ± 10 Ma . Rutile (Metcalf et al, 2018).…”

“…Increasing the range of minerals that can be used as (U-Th)/He thermochronometers has the potential to broaden the spectrum of lithologies on which the method can be applied and improve the completeness, detail, and reliability of thermal history interpretations. Thus, much recent work has focused on developing and applying the (U-Th)/He method on phases such as magnetite (e.g., Blackburn et al, 2007), spinel (e.g., Cooperdock & Stockli, 2018), goethite (e.g., Heim et al, 2006;Reiners et al, 2014), hematite (e.g., Ault et al, 2015;Farley & Flowers, 2012;Farley & McKeon, 2015), calcite (e.g., Copeland et al, 2015;Cros et al, 2014), and perovskite (Stanley & Flowers, 2016).…”

The effects of 10 to >160 GPa shock on the magnetic properties of basalt and diabase

“…Accordingly, T v is conventionally defined as the peak on the first derivative of the warming curve of a zero‐field‐cooled (ZFC) remanent magnetization acquired below T v [ Özdemir and Dunlop , ] (Table ). Another method for determining the Verwey transition is to determine the median demagnetization temperature of ZFC remanence during zero‐field warming [ Carporzen and Gilder , ], referred to as T d [ Sato et al ., ] (Table ).…”