Full vector low‐temperature magnetic measurements of geologic materials

Abstract

The magnetic properties of geologic materials offer insights into an enormous range of important geophysical phenomena ranging from inner core dynamics to paleoclimate. Often it is the lowtemperature behavior (<300 K) of magnetic minerals that provides the most useful and highest sensitivity information for a given problem. Conventional measurements of low-temperature remanence are typically conducted on instruments that are limited to measuring one single-axis component of the magnetization vector and are optimized for measurements in strong fields. These instrumental limitations have prevented fully optimized applications and have motivated the development of a low-temperature probe that can be used for low-temperature remanence measurements between 17 and 300 K along three orthogonal axes using a standard 2G Enterprises SQuID rock magnetometer. In this contribution, we describe the design and implementation of this instrument and present data from five case studies that demonstrate the probe's considerable potential for future research: a polycrystalline hematite sample, a polycrystalline hematite and magnetite mixture, a single crystal of magnetite, a single crystal of pyrrhotite, and samples of Umkondo Large Igneous Province diabase sills.

The effect of hydrostatic pressure up to 1.61 GPa on the Morin transition of hematite‐bearing rocks: Implications for planetary crustal magnetization

“…By replacing the sample by a thermocouple in the cell, we constructed a temperature versus time model (see section 3.1 and Figure ). The Morin transition temperature T M was determined as the maximum in the first derivative of remanence warming curve (in accordance with Feinberg et al []). The T M value determined in this way at atmospheric pressure is in accordance with Özdemir et al [], who indicated T M ranging from 250 K to 261 K for 0.5–6 mm hematite natural single crystals and from 257 K to 260 K for 45–600 µm sieved crystal fractions.…”

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

“…Stoichiometric magnetite is characterized by a crystal symmetry transition from cubic to monoclinic upon cooling through the Verwey transition temperature T v ≈ 120 K [ Verwey , ]. This transition affects many physical properties [e.g., Honig , ], including magnetocrystalline anisotropy [ Abe et al ., ], so that cooling and warming cycles of remanent magnetization across T v are characterized by an inflection in remanent magnetization [ Feinberg et al ., ]. 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 ).…”

The end of Midcontinent Rift magmatism and the paleogeography of Laurentia

“…This low-temperature step was implemented with the goal of preferentially removing remanence associated with multidomain magnetite. Many such multidomain grains undergo low-temperature demagnetization when cycled through the isotropic point (~130 K) and the Verwey transition (~120 K; Verwey, 1939;Feinberg et al, 2015). Subsequently, the samples were progressively step-heated and thermally demagnetized in an ASC thermal specimen demagnetizer (residual fields <10 nT).…”