1. Prototyping a new, high-temperature SQUID magnetometer system
J. Michael Grappone, John Shaw, and Andrew J. Biggin
Technical Summary
Introduction
Initial results: demagnetization
The solid-state uniaxial design runs demagnetization surveys, and remagnetization is in the works
Our goal is a new cost-effective, versatile continuous magnetometer system for tailored paleointensity experiments
+ RF-SQUID continuous thermal magnetometer
+ 700°C maximum temperature (PID controlled)
+ < 3L/day liquid nitrogen used
+ Sensitivity ∼ 0.5 nT for a single 7 mm diameter sample
+ Continuous data recording
+ RF-SQUIDs and Mu-Metal provide high resolution capabilities
+ Liquid nitrogen operating temperature reduces costs
+ Precise ovens ensure reproducibility
+ No cooling step between heating steps reduces experiment time
+ Lower possibility of alterations compared to step-wise experiments
+ Solid-state magnetometers avoid mechanical complexity
and sample damage
16 nT≈5.5× 10 −7 A m 2
Single-axis magnetometer prototype
Future additions
The complete prototype will be able to run a full paleointensity survey
Successful demagnetization of artificial basalt samples demonstrates the magnetometer system’s current capabilities
+ Top loading for better consistency
+ Internal RF shielding
+ Larger liquid nitrogen Dewar
+ Sample alignment
+ Curves smoothed over 0.2s (0.1 °C)
+ Similar shapes; different magnitudes
- Non-ideal testing environment
- Questionable reproducibility of applied remagnetization & sample orientation
2 more SQUIDs
Conclusions
TRM coil
The single-axis prototype shows promise that temperature gradients can be handled without major sensitivity losses
Cooling system
(post-survey)
+ Can extract uniaxial data for stronger samples
+ Low noise levels imply potential for weak magnetizations
- One sample/hour not fast enough; needs post-survey cooling system
- Controlling nitrogen bubbles problematic
Separate Dewar
Speed
Sensitivity
Our new system will improve measurement rate, while still allowing tailoring of paleointensity studies
References
Chamalaun, F. H., and Porath, H., 1968, A CONTINUOUS THERMAL DEMAGNETIZER FOR
ROCK MAGNETISM: Pure and Applied Geophysics, v. 70, no. 2, p
Goree, W. S., and Fuller, M., 1976, MAGNETOMETERS USING RF-DRIVEN SQUIDS AND
THEIR APPLICATIONS IN ROCK MAGNETISM AND PALEOMAGNETISM: Reviews of
Geophysics, v. 14, no. 4, p
Le Goff, M., and Gallet, Y., 2004, A new three-axis vibrating sample magnetometer for
continuous high-temperature magnetization measurements: applications to paleo- and
archeo-intensity determinations: Earth and Planetary Science Letters, v. 229, no. 1-2, p.
31-43.
Matzka, J., 2001, Besondere magnetische Eigenschaften der Ozeanbasalte im
Altersbereich 10 bis 40 Ma Ph.D.: Ludwig-Maximilians-Universität München.
Poidras, T., Camps, P., and Nicol, P., 2009, Controlled atmosphere vibrating thermo-
magnetometer (CatVTM): a new device to optimize the absolute paleointensity
determinations: Earth Planets and Space, v. 61, no. 1, p
Schmidt, P. W., and Clark, D. A., 1985, STEP-WISE AND CONTINUOUS THERMAL
DEMAGNETIZATION AND THEORIES OF THERMOREMANENCE: Geophysical Journal of
the Royal Astronomical Society, v. 83, no. 3, p
+ No intermediate cooling
+ Single sample 
experiment tailoring
+ Baseline above overprint
+ More data points
+ Lower alteration
- No batch capabilities
Oven noise
Noise data were determined by running five empty oven demagnetization tests and comparing the resulting curves. The residual noise shown is 3𝝈.