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Magnetic susceptibility reflects a material's degree of sensitivity to magnetic fields. Some materials are highly susceptible and will become magnetized in response to a magnetic fields, while others resist magnetism, depending on their composition. It is possible to test this trait in the lab to come up with an absolute measurement that may provide information about a sample of interest. Such testing can be a routine part of evaluations of certain geological samples where researchers want to learn more about their structure and composition.
In a test to determine magnetic susceptibility, the technician needs to control the environment to limit interference and generate usable, replicable results. These measurements are temperature dependent, which makes it important to conduct testing at a stable temperature. Magnetic fields in the environment should also be controlled to keep the measurements clean. Standardized equipment is available to hold the sample, generate a magnetic field, and record the results.
Technicians can express magnetic susceptibility as a ratio between the amount of magnetism induced in the sample and the amount generated by the field. Ratios above one are indicative of magnetic susceptibility. Some materials can generate very high ratios, indicating that they are highly susceptible. If no response is induced, the material has a susceptibility of zero. Charts are available to provide information on the susceptibility of known materials in controlled conditions.
Test results can be compared to charts by a technician interested in finding out what is inside a sample. Other properties can be measured with additional testing to collect more data. Multiple samples from the same area may be tested to generate a chart, mapping out the changes in susceptibility over a given area of terrain. This information can all be helpful for mapping out the content and structure of rock and soil formations for activities like prospecting and field research.
Lab equipment to measure magnetic susceptibility is available from scientific suppliers, particularly those who focus on geology. It is also possible to build testing units, if a researcher is comfortable with designing and assembling testing components. Known reference materials can be used to calibrate the equipment to confirm it is in working order before testing unknown samples. Such calibration is important to ensure the validity of the test results. When testing is used in scientific research the calibration and testing methods need to be discussed in the writeup for the benefit of readers and reviewers.