Development of a low‐temperature insert for the measurement of remanent magnetization direction using superconducting quantum interference device rock magnetometers

Abstract

[1] Data on the directional changes of a full magnetization vector during cycling to cryogenic temperatures can provide important insights into the low-temperature magnetic properties of natural and synthetic materials. These data also provide an empirical basis for the application of low-temperature treatments in paleomagnetism, for example, the removal of viscous magnetization in magnetite-bearing rocks. However, existing instruments only allow continuous measurement of magnetization along a single axis, hampering experimental and theoretical advances in rock magnetism and the implementation of low-temperature techniques into regular paleomagnetic practices. Here we describe development of a novel low-temperature insert designed in collaboration with William S. Goree Inc., which allows measurement of directional behavior of a full magnetization vector during zero-field low-temperature cycling. Pilot experiments on wellcontrolled polycrystalline samples of pseudo-single-domain (PSD) and multidomain magnetite as well as on a natural sample containing PSD magnetite indicate that the orientation of a saturation isothermal remanent magnetization (SIRM) imparted at room temperature remains constant during low-temperature cycling to 20 K. This observation lends additional support to low-temperature cycling as a cleaning technique in paleomagnetism. The SIRM imparted in an individual crystal of magnetite showed systematic, albeit small changes upon both cooling and warming through the Verwey temperature, which may reflect switching between the easy magnetization directions. However, the switching effect may be significantly attenuated by crystallographic twinning in magnetite below the transition. Overall, our results demonstrate the potential of the directional low-temperature magnetometry for the advancement of our understanding of the properties of natural and synthetic materials.

Full vector low‐temperature magnetic measurements of geologic materials

“…1. To demonstrate that the temperature-dependent intensity data acquired using the IRM-LTI is virtually identical to that acquired using MPMS instruments (as shown by Smirnov and Tarduno [2011] for the ST-LTI), which should give confidence to potential users.…”

“…Thus, the remanence imparted along the cubic magnetocrystalline easy axis was marginally more resistant to low‐temperature demagnetization than those imparted along the intermediate or hard axes. On continued cooling through T v , the remanence increases abruptly and significantly (Figure c), unlike the behavior commonly observed for polycrystalline MD powder samples in MPMS experiments, but similar to that found in previous single‐crystal measurements [e.g., Özdemir and Dunlop , ; Smirnov and Tarduno , ]. The magnitude of remanence below the Verwey transition is also somewhat anisotropic with the ratio of remanence at 20 K to that at 260 K for each IRM at 53%, 61%, and 56%, respectively.…”

“…The five case studies that follow serve three primary purposes: To demonstrate that the temperature‐dependent intensity data acquired using the IRM‐LTI is virtually identical to that acquired using MPMS instruments (as shown by Smirnov and Tarduno [] for the ST‐LTI), which should give confidence to potential users. To demonstrate the utility of three‐axis full‐vector magnetic measurements in several different rock magnetic and paleomagnetic applications. In the course of doing so, novel results have been obtained. To inspire new uses for the IRM‐LTI, and in some instances, we have provided suggestions for future studies that we have not yet explored. …”

“…The approach and technical design of the LTI in this study (IRM‐LTI) builds on ideas of an earlier effort by the late William Goree of 2G Enterprises along with Aleksey Smirnov and John Tarduno [ Smirnov and Tarduno , ]. The key innovation of that collaborative effort was the design of a low‐temperature instrument (that we will refer to as the ST‐LTI) that could be inserted into a standard bore 2G Enterprises cryogenic rock magnetometer.…”

“…This instrument allows for three‐axis full‐vector measurements of magnetic remanence at temperatures between 300 and 17 K in low‐field environments (<10 nT). It was developed with different engineering, but the same intent, as a low‐temperature insert that has previously been implemented at the University of Rochester Paleomagnetic Laboratory [ Smirnov and Tarduno , ].…”