[Europan Ocean (OP)]

Is there a large percentage of cobalt in the Earth's core? Can a planet generate a magnetosphere with Cobalt?

[evan_au]

The core of the Earth is believed to consist mainly of a nickel-iron alloy, similar to nickel-iron meteorites.
Other elements are mixed in with this alloy, and cobalt is one of the most common of the minor components.

Cobalt is a ferromagnetic metal, which means that it responds strongly to magnetism at room temperature. However, temperatures in the Earth's outer core are believed to be in the range 4400C-6100C, well above Cobalt's Curie temperature of 1115C, so it will not be magnetic in this environment (nor will iron, with a Curie temperature of 770C or Nickel, at 355C).

The Earth's magnetic field is thought to be produced by electrical currents in the Earth's liquid outer core, driven by convection and possibly differential rotation between the inner core and the mantle. These currents do not need to occur in a magnetic material - laboratory experiments to reproduce the effect have used liquid Sodium, which is non-magnetic.

So to summarise - there is some Cobalt in the Earth's core, and a magnetic field can be generated in a molten Nickel-Iron alloy that contains Cobalt.