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Paleomagnetism Laboratory


Logistics and Laboratory equipment

 

Logistics

Since 1993, the INGV paleomagnetic laboratory is equipped with a shielded room in order to operate in an environment protected from static magnetic fields (such as the Earth’s magnetic field); this magnetically shielded room allows the housing of two cryogenic magnetometers and all the equipment that must operate without the influence of magnetic fields.
The intensity of the magnetic field inside the room screen is reduced to a few thousandths of the Earth’s magnetic field (in Rome about 45000 nT); the instruments inside the room also has additional μ-metal shields to insulate them also from the variable magnetic fields (fig. 1).
The paleomagnetic laboratory also benefits from a adjoining room where the instruments that do not require magnetic screening are installed, and a small refrigerated room for the storage of cores and u-channel samples.

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Figure 1 Full view of the magnetically shielded room of the paleomagnetic laboratory.

 

Laboratory Equipment

This section lists and briefly describes the main instruments used in the INGV paleomagnetism laboratory.

  • 2G Cryogenic Magnetometer (installed in 1996 – Fig. 2)

Magnetometer with DC SQUID sensors based on the superconductivity of junctions at liquid helium temperature (4K), for the measurement of both standard discrete (cylinders of rock to 2.5 cm in diameter 2.2 cm high) and continuous paleomagnetic samples (u-channels of up to 1.5 m in length and a square section of 1.9 cm side) . The magnetometer is equipped with in-line equipment, which can be computer controlled and operated. This equipment includes a system of three orthogonal coils for alternating magnetic field (AF) degaussing of the samples, with the possibility of imparting anhysteretic remanent magnetization (the magnetization produced for simultaneous application of a magnetic alternate field and a constant magnetic field) and a pulse magnet that can produce a maximum axial magnetic field of 0.9 T. This magnetometer keeps the low temperature thanks to a 60 l reservoir of liquid helium, enough for about 1.5 years of operation.

Figure 2 Our first cryogenic magnetometer from 1999.
  • 2G Cryogenic Magnetometer liquid-helium-free (installed in 2006)

The features are similar to the previous model, but it works with a new generation cooling system which doesn’t need the 60 l reservoir; it guarantees operation without helium periodical fillings.

  • AGICO Spinner Magnetometers (JR-4, JR-5 and JR-6 – Fig. 3)

These magnetometers operate  according to the Faraday-Neumann law; the sample rotates up to 90 cycles/s inside a pair of coils, producing an induced electromotive force proportional to the remanent magnetization of the sample. These magnetometers are very reliable but less sensitive than cryogenic magnetometers. Especially recommended for high magnetized samples which saturate the cryo system.

Figure 3 The JR-6A spinner magnetometer.
  • Princeton Micromag 2900/3900 AGM/VSM Magnetometer, Princeton Measurement Corp. (Fig. 4)

High precision and sensitivity instrument for measuring hysteresis loops and other magnetic properties; the sensitivity is 10 nemu as alternating gradient magnetometer and 0.5 μemu as vibrating sample magnetometer. The VSM is equipped with a variable temperature cryostat device operating in 10 to 473K temperature range.

Figure 4 The Micromag magnetometer, for high-sensitivity hysteresis loops.
  • Molspin Vibrating sample magnetometer (Fig. 5)

Magnetometer for studying the hysteresis loops of 0.5 cm3 powder samples; the low sensitivity makes it inappropriate in the case of weak ferromagnetic contribution.

Figure 5 The Molspin VSM, to study hysteresis loops on powder samples.
  • Pyrox and ASC Scientific thermal demagnetizer (Fig. 6)

Ovens for the thermal demagnetization of paleomagnetic samples up to 700°C.

Figure 6 The Pyrox oven and its controller, to demagnetize up to 700 °C.
  • 2G Pulse magnetizer (Fig. 7)

Tool to apply a pulse magnetic field up to 2.7 T, in order to impart an isothermal remanent magnetization.

Figure 7 The 2G pulse magnetizer, the field can reach up to 2.7 T
  • AGICO Kappabridges (mod. KLY-2, KLY-3S and MFK1_FA – Fig.8)

Instruments for measuring the magnetic susceptibility and its anisotropy on both cylindrical and cubic samples. Both Kappabridges are coupled to a furnace (CS-2, CS-3) for the measurement of the variation of magnetic susceptibility during a cycle from room temperature up to 700 ° C and back. The MFK1_FA multifunction kappabridge multifunzione ha been installed in 2008 and it is equipped with the CS-L apparatus which allows the measurement of the variation of magnetic susceptibility also in low-temperature cycles up to the temperature of liquid nitrogen (ca. - 196°C).

Figure 8 AGICO MFK1-FA susceptibility meter, conected to the fornace for measuring the variation of susceptibility vs temperature.
  • AF demagnetizer LDA-3A and AMU-1A anhysteretic magnetizer, AGICO (Fig. 9)

Alternating field demagnetizer for standard paleomagnetc samples, equipped with a device for the production of anhysteretic remanence magnetization.

 

Figura 9 AF demagnetizer LDA-3A produced by AGICO
  • Bartington Susceptibility Meter (MS2 – Fig. 10)

Magnetic susceptibility meter, with MS2B sensor for standard cylindrical samples (2 frequencies of operation) and with sensor MS2C for continuous samples, in line with the cryogenic magnetometer.

Figure 10 Bartington susceptibility probe MS2C, mounted in-line with cryogenic magnetometer.

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