Magnetic susceptibility is a measure of the ease with which particular sediments are magnetized when subjected to a magnetic field.  The ease of magnetization is ultimately related to the concentration and composition (size, shape and mineralogy) of magnetizable material contained within the sample.  Any sediment core possessing downcore variation per unit volume in the concentration and composition of magnetizable minerals will yield a MS curve reflecting these changes.

In our system, whole cores are moved incrementally (generally in 1cm) by a track motor through a susceptibility loop (of varying size) in which a magnetic field is generated and which magnetizes the sample susceptible substances (minerals or mineraloids) within the sediment.  Samples that are rich, per unit volume, in magnetizable substances will yield high readings.  Samples that are poor in magnetizable substances,  or contain diamagnetic minerals, will yield lower or negative values

Magnetizable minerals include the ferromagnetic minerals (strongly magnetizable) and any of the paramagnetic (moderately magnetizable) minerals and other substances.  The former include magnetite, hematite, iron titanium oxides, pyrrhotite, maghemite, greigite and goethite, minerals capable of acquiring remnant magnetization and useful for paleomagnetic studies.  The latter include a broad array of substances all of which contain Fe2+, Fe3+, or Mn2+ ions.  These paramagnetic minerals may include clay minerals (chlorite, smectite and glauconite), iron and manganese carbonates (siderite, rhodochrosite), ferromagnesian silicates (olivine, amphiboles, pyroxenes, etc.),  as well as a variety of ferric-oxyhydroxide mineraloids.

LRC Magnetics Instrumentation

LRC maintains a Bartington Instruments MS2 magnetic susceptibility meter, sensors MS2B and C, as part of the multi-sensor track logging system (MSTL), as well as MS2 field survey equipment..  The system is a non-destructive method of obtaining high resolution (1cm) measurement of magnetic susceptibility (MS) from whole cores (other systems are designed to work with split cores).  The system also can be used to measure single sample susceptibility.  The MSTL forms the first step in the initial core studies, prior to splitting the cores.   The basic principles of the method, and some examples of its applications in paleolimnology are discussed below.

 For whole core measurements, we have designed a maple magnetic susceptibility track. This track is 3.2 meters long and includes a Kevlar timing belt and a PVC boat which can accommodate a core up to 7.5 cm in diameter. The MS2C core logging sensor is attached to the track. This sensor is 100 mm in diameter and provides high precision volume susceptibility measurements on whole cores. It is suitable for measuring any type of peat, lake or marine sediment core, provided the core is not metal clad. The instrument has a precision of 1 x 10-6 cgs and can log cores at intervals down to ca. 20 mm

The single sample sensor MS2B is designed for use with 1" and 7/8" cubic boxes. Sample insertion and removal is facilitated by a hand operated moving platen. This sensor is used for measurements on standard paleomagnetic samples in studies of rock and mineral magnetism and anisotropy of susceptibility. The dual frequency facility allows confident identification of ferrimagnetic stable single domain transition. It is accurate to 2 x 10-7 cgs for both high and low frequencies.

Procedure

    NOTE:  The geotek can only be operated by a qualified technician due to the radiation hazard.
1.  Turn on the geotek microprocessor and boot up the Geotek Master software.
2.  Select "Log New Core," and type name of core.
3.  Select desired sensors (Gamma ray densitometer, p-wave sensor, magnetic susceptibility, etc.) and enter core length and description.  Enter OK.
4.  Place core in PVC boat and secure with end stops.
5.  Switch the track to manual  operation, and bring the bottom of the core to a point even with the leading edge of the p-wave sensors.
6.  Switch track  to automatic, and click "Set Ref."   Using the boat icon, drag the core back until  the top of the core is even with the leading edge of  the p-wave sensors.
7.  Open the gamma ray shutter, and if using the p-wave sensor, wet both the sensor and the core with a sponge.
8.  Select "Begin Logging."  The data is saved automatically.

Information provided by: http://lrc.geo.umn.edu