Magnet
Rare earth (lanthanoid) elements have a partially occupied "f" electron shell (which can accommodate up to 14 electrons). The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore, these elements are used in compact high-strength magnets where their higher price is not a concern. The most common types of rare-earth magnets are samarium-cobalt and neodymium-iron-boron (NIB) magnets.
Environmental magnetism
Environmental magnetism is built on two parts of rock magnetism: magnetic mineralogy, which looks at how basic magnetic properties depend on composition; and magnetic hysteresis, which can provide details on particle size and other physical properties that also affect the hysteresis. Several parameters such as magnetic susceptibility and various kinds of remanence have been developed to represent certain features of the hysteresis. These parameters are then used to estimate mineral size and composition. The main contributors to the magnetic properties of rocks are the iron oxides, including magnetite, maghemite, hematite; and iron sulfides (particularly greigite and pyrrhotite). These minerals are strongly magnetic because, at room temperature, they are magnetically ordered (magnetite, maghemite and greigite are ferrimagnets while hematite is a canted antiferromagnet).