Magnetic Properties of Hematite

Below 250 Kelvin

• Hematite is "antiferromagnetic" below the temperature threshold called the "Morin transition," which is 250 kelvin (-9.6 F, or -23.2 C). The term antiferromagnetic refers to the way in which individual molecules align their magnetic poles. At these low temperatures, the molecules of hematite align themselves so that neighboring molecules' magnetic poles are pointed in opposite directions. This causes the magnetic fields to essentially cancel each other out, so a chunk of magnetite below 250 kelvin will not show obvious magnetism.

Between 250 K and 948 K

• Above the Morin transition temperature threshold of 250 K, hematite is weakly "ferromagnetic," which is also referred to as being a "canted antiferromagnet." For example, more of the individual molecular magnetic poles of the mineral are pointed in one direction than the other, so there is a net magnetic field, but it is not as strong as if all of the poles pointed in the same direction. The strength of this ferromagnetic field varies depending on the impurities of any given sample of hematite.

Above 948 K

• Hematite's magnetic properties change again above 948 K, which is referred to as its "Néel temperature." Above this temperature, which can also be expressed as 674.9 C or 1246.7 F, hematite is "paramagnetic." In this state, the thermal energy of the mineral is so high that it disrupts any particular arrangement of molecular orientations that would normally produce magnetism. Paramagnetic materials are attracted to other magnetic fields, but once the external field is removed, they no longer retain any magnetism.