Paleo and Rock Magnetism

Magnetically shielded room

Magnetically shielded room

Marine cores consist of rocks and sediments, which contain a variety of magnetic particles. These rocks and sediments acquire remanent magnetizations in response to the Earth's magnetic field at their formation or deposition, and the magnetizations are preserved over geological time as `fossils'. One can determine (calculate) the fossil magnetizations by measuring magnetic field produced by them.

Fossil magnetizations preserved in rocks and sediments are generally very weak and thus magnetic field produced by them is also very weak. 'Magnetically clean' environment is necessary to detect and measure this very weak field. The Kochi Core Center has a magnetically shielded room which is surrounded by three layers of permalloy metals (alloys of iron and nickel). The residual field inside the room is about 0.2 per cent of the field outside and the room is one of the biggest `shielded rooms' in the world.

A variety of instruments are placed in this shielded room: pass-through superconducting magnetometers; spinner magnetometer; kappa bridge; thermal and AF demagnetizers.

Pass-through Superconducting Magnetometer for U-Channel Samples

Pass-through Superconducting Magnetometer for U-Channel Samples

This instrument utilizes high-sensitivity superconducting quantum interference device (SQUID) sensors which are capable of measuring very weak magnetizations recorded in geologic materials. One can measure remanent magnetizations with stepwise AF demagnetization treatments on a fully automatic basis, including applications of artificial remanence in laboratory (ARM). It is tailored to continuous measurements of U-channel samples, but measurements of discrete samples are also possible.
Model
Model 760R (U-channel), 615L
Manufacture
2G
Operating condition
measurable sample size 1-inch paleomagnetic cylindrical samples (or smaller), U-channel samples (up to 150 cm)
minimum measurable magnetization 1×10e-7 emu (1×10e-10 Am2)
AF field 0〜80 mT
DC field (for ARM) 0~0.1 mT
Lab.
Paleo & Rock Magnetism

MPMS

Pass-through Superconducting Magnetometer for U-Channel Samples

The magnetic property measurement system (MPMS) measure magnetizations and magnetic susceptibilities of samples using SQUID sensors under controlled magnetic field and temperature. Magnetic field is created by a built-in superconducting magnet and temperature is controlled by evaporated liquid helium. It is often used to determine the types of magnetic minerals contained in the sample by detecting sub-room-temperature phase transformations characteristic to individual magnetic minerals (e.g. 110 K Verwey transition of magnetite).
Model
MPMS-XL5
Manufacture
Quantum design
Operating condition
maximum sample size phi 4mm x length 9mm
temperature 1.9〜400 K
DC field -5 〜 +5 T
minimum measurable magnetization 1×10e-7 emu
Lab.
Paleo & Rock Magnetism

VSM

VSM

Vibration of a sample in a steady magnetic field induces electromotive force in vicinity coils. The vibrating sample magnetometer (VSM) measures magnetization of the sample by amplifying the induced electronic signals in the coil. One can control dynamically the magnetic field and temperatures so that it is possible to obtain magnetic hysteresis loops (M-H curves) and thermomagnetic curves (M-T curves).
Model
MicroMag 3900
Manufacture
Princeton Meas. Co.
Operating condition
maximum sample weight less than 100 mg
 temperature room temp. 〜 700 ℃
DC field -1.8 〜 +1.8 T
minimum measurable magnetization 1×10e-4 emu
Lab.
Paleo & Rock Magnetism

Magnetic Balance

Magnetic Balance

This instrument enables thermomagnetic experiments. One can obtain thermomagnetic curves (M-T curves) and determine the Curie temperature of a sample.
Model
NMB-89
Manufacture
Natsuhara-Giken
Operating condition
measurable sample dried powder or fragments (less than 100 mg)
temperature room temp. 〜 700 ℃
DC field 0 〜 +0.8 T
Lab.
Paleo & Rock Magnetism

Kappa Bridge

Kappa Bridge

One can measure magnetic susceptibility and its anisotropy of core samples.
Model
KLY-3S
Manufacture
Agico
Operating condition
measurable sample

(room temp.)

1 inch paleomagnetic cylindrical sample (or smaller)

(-192 ℃ 〜 room temp., room temp. 〜 700 ℃)

powder, susceptibility only

minimum measurable susceptibility 1×10e-6 SI
Lab.
Paleo & Rock Magnetism

Spinner magnetometer

Spinner magnetometer

This instrument enables measurements of remanent magnetization of igneous and metamorphic rocks which generally have strong magnetizations, by rotating samples around several flux-gate magnetometers. Remanent magnetizations of some sedimentary rocks are also measurable.
Model
SMD-88
Manufacture
Natsuhara-Giken
Operating condition
measurable sample 1 inch paleomagnetic cylindrical sample (or smaller)
minimum measurable magnetization 1×10e-5 emu (1×10e-8 Am2)
Lab.
Paleo & Rock Magnetism

Thermal demagnetizer

Thermal demagnetizer

This is a specially designed electronic furnace, sample space of which is surrounded by three layers of permalloy metals. One can thermally magnetize and demagnetize samples.
Model
TDS-1
Manufacture
Natsuhara-Giken
Operating condition
oven temperature room temp. 〜 700 ℃
residual field at the sample space less than 10 nT
DC field for magnetization 0〜100 micro-T
Lab.
Paleo & Rock Magnetism

Alternating Field (AF) demagnetizer

Alternating Field (AF) demagnetizer

There are three layers of permalloy metals outside the sample space, and a sample is set to a two-axis tumbler which rotates inside an AF-generating coil. One can iso-thermally magnetize and demagnetize samples utilizing AF field.
Model
DEM-95
Manufacture
Natsuhara-Giken
Operating condition
measurable sample 1 inch paleomagnetic cylindrical sample (or smaller)
AF filed 0.2〜180 mT
Lab.
Paleo & Rock Magnetism

Pulse magnetizer

Alternating Field (AF) demagnetizer

This instrument can apply pulse strong magnetic field to a sample, imparting isothermal remanent magnetization (IRM).
Model
MMPM10
Manufacture
Magnetic Measurements
Operating condition
pulse field 0-9 T (1.25 cm coil), 0-3 T (3.8 cm coil)
Lab.
Paleo & Rock Magnetism
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