Paleo and Rock Magnetism

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

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

Operating condition

measurable sample size	1-inch paleomagnetic cylindrical samples (or smaller), U-channel samples (up to 150 cm)
minimum measurable magnetization	1ÁE0e-7 emu (1ÁE0e-10 Am2)
AF field	0、E0 mT
DC field (for ARM)	0 \| E.1 mT

Lab.

Paleo & Rock Magnetism

MPMS

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、E00 K
DC field	-5 、E+5 T
minimum measurable magnetization	1ÁE0e-7 emu

Lab.

Paleo & Rock Magnetism

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. 、E700 ℁E
DC field	-1.8 、E+1.8 T
minimum measurable magnetization	1ÁE0e-4 emu

Lab.

Paleo & Rock Magnetism

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. 、E700 ℁E/td>
DC field	0 、E+0.8 T

Lab.

Paleo & Rock Magnetism

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 ℁E、Eroom temp., room temp. 、E700 ℁E

powder, susceptibility only

minimum measurable susceptibility

1ÁE0e-6 SI

Lab.

Paleo & Rock Magnetism

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	1ÁE0e-5 emu (1ÁE0e-8 Am2)

Lab.

Paleo & Rock Magnetism

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. 、E700 ℁E/td>
residual field at the sample space	less than 10 nT
DC field for magnetization	0、E00 micro-T

Lab.

Paleo & Rock Magnetism

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