When you think of magnetic metals, the three ferromagnetic elements come to mind: cobalt, nickel and iron. It is also not surprising that some of the alloys containing these metals are also ferromagnetic such as steel as well as some of the crystalline compounds like iron oxide (Fe2O3). Now although these are stated as the only ferromagnetic elements there is a caveat. Perhaps it would be more accurate to say that they are the only ferromagnetic elements at room temperature. Materials have what is called a Curie temperature. This is a critical point at which the permanent magnetic dipoles get scattered by the heat resulting in the loss of permanent magnetism and the onset of induced magnetism. The elements dysprosium (Dy), terbium (Tb) and gadolinium (Gd) are also ferromagnetic with terbium and gadolinium needing to be cooled to 219 K and 292 K respectively and dysprosium requiring an extremely low 88 K.
For a long time, it was the iron in the Earth’s core that was used to explain geomagnetism. As the temperatures at the centre of the Earth are far past iron’s Curie point, it was a flowing dynamic action that was used to explain the generated magnetic field. Originally it was thought that nickel could not play a role in this field production as the Earth’s magnetic field has its origin in the outer core, while nickel is in the inner. But recent models seem to show that the energy the core produces cannot maintain the outer core’s movement at a rate which produces the observed magnetic field and so the inner core, about a fifth of which is nickel, becomes a focus.