Superconducting Rock Magnetometer (SRM)

Overview

The measurement of remnant magnetic signatures in sediment cores, rocks, and geological samples aids in the reconstruction of Earth’s magnetic field history. The superconducting rock magnetometer (SRM) uses superconducting quantum interference detectors (SQUIDs) and operating at cryogenic temperatures is able to detect weak magnetic signals in geologic samples. The unit includes mu-metal shielding, and an alternating field demagnetizer for all three axes.

Maximum core diameter: 7.4 cm (o.d.)
Maximum core length: 155 cm

Instrument Make & Model

2G Enterprises Model 760-4K Superconducting Rock Magnetometer
2G Enterprises Model 2G600 In-line Automatic Sample Degaussing System

Estimated Measurement Time

Measurement Time: 5–20 mins/section

Principles & Analytical Capabilities

The SRM may be configured to measure core sections (whole or split) or discrete samples. Specialized fiberglass trays are available for both configurations.

Due to instrument geometry and SQUID orientation, the response length of each SQUID is unique (X=7.3 cm, Y=7.3 cm, Z=9 cm). Each measurement is therefore influenced by the volume of the core within the response area. Fine resolution (<2cm) measurements are not recommended.

Typical measurement resolution:

Sections: 2-5 cm. Users have operated the system outside of this resolution range when deemed necessary for experimental or timing needs.
Discrete Samples: 8 samples in a 155 cm tray

The SRM may be used to measure discretes after various offline treatment procedures, or with inline demagnetization treatment. The custom software allows the user to specify the type of treatment and initiate measurements.

Offline Treatment Options:

AF demag (DTECH D-2000 AF demagnetizer/partial anhysteric remanent magnetizer
Thermal demag (ASC TD-48 thermal demagentizer)
Cryogenic demag (liquid nitrogen)
Imparted field (ASC IM-10 impulse magnetizer)

Data Generated

Data components:

Treatment Type: type of remanent magnetization measured. Default is natural remanent magnetization (NRM) but other types include anhysteretic (ARM) and isothermal (IRM).
Treatment Value: value of offline treatment that was applied to the sample being measured (e.g., thermal demagnetization °C).
Inclination background + tray corrected (°): inclination computed with tray and background (drift) correction.
Declination background + tray corrected (°): declination computed with tray and background (drift) correction.
Intensity background + tray corrected (A/m): intensity computed with tray and background (drift) correction.
Inclination raw (°): inclination computed from magnetic moment data.
Declination raw (°): declination computed from magnetic moment data.
Intensity raw (A/m): intensity computed from magnetic moment data.
Magnetic moment x|y|z (Am2): magnetic moment raw data from SQUID axes, with sign corrected to match IODP orientation conventions.

Data files:

Data file (SRM): text file containing reduced data and metadata
Results (CSV): tabular file containing final and intermediate SRM calculation data, rotational data, flux counts, etc. [in development; currently use SRM file]
Parameters (CSV): tabular file containing parameters, tray definition, and raw and drift corrected values for SQUID XYZ readings

Data Example

Graph of [copy from caption]. — Intensity, declination, and inclination paleomagnetic measurements from Hole U1554A of IODP Expedition 384 (for IODP Expedition 395) on the eastern flank of the Reykjanes Ridge in the North Atlantic Ocean.¹

Procedures & Manuals

References

¹Parnell-Turner, R. E., Briais, A., LeVay, L. J., Cui, Y., Di Chiara, A., Dodd, J. P., Dunkley Jones, T., Dwyer, D., Eason, D. E., Friedman, S. A., Hemming, S. R., Hochmuth, K., Ibrahim, H., Jasper, C., Karatsolis, B. T., Lee, S., LeBlanc, D. E., Lindsay, M. R., McNamara, D. D., … Tian, C. Y. (2025). IODP Expedition 384 Magnetic remanence (SRM-longcore) [Data set]. International Ocean Discovery Program. https://doi.org/10.5281/zenodo.15122429