When the geologist takes the sample back to the lab they use a device called a magnetometer to measure the intensity and direction of the magnetic field of the rock sample. There are two types of magnetometers that can be used. The spinner magnetometer is used for samples that are strongly magnetized. The spinner magnetometer rotates the sample rapidly within a coil around an axis. The magnetometer measures the electrical current created in the coil by the spinning sample. The sample is spun in various orientations to determine the intensity and direction of the magnetic vector. The drawback of the spinner magnetometer is that it only works with strongly magnetized and highly coherent samples, such as those from igneous rocks.
A second type of magnetometer is the cryogenic magnetometer. Cryo is the Latin prefix for cold, and the cryogenic magnetometer uses liquid helium at 4 degrees Kelvin (K) to create a very cold superconducting region around the magnetometers sensors. (4 degrees K is four degrees above absolute zero - absolute zero is the ultimate freezing point. The average temperature of the universe is 3 degrees K.) At such cold temperatures electrical currents move with nearly no resistance. When the magnetized is placed into the sensor area the sample's magnetic field sets up a current in the superconducting coil. This current can then be measured. The cryogenic magnetometer is 3 to 4 times more sensitive than the spinner magnetometer and is capable of measuring even the weakest magnetized sample. Even the magnetic properties of liquids and live animals can be measured by a cryogenic magnetometer since the sample does not need to be spun.
