Geomagnetism and Temperature
Date: Spring 2013
Often, the answer about Earth's magnetism is that it is due to the moving iron core. But Earth's moving core is more than 6000 degrees Celsius. How can it behave as a magnet at that 'Very High' temperature (higher than the Curie Point) where even Iron melts?
You are correct that Earth's core exceeds the Curie temperature of its component materials. The cause of Earth's magnetic field is the dynamo action of charged particles in the outer, fluid core of the planet.
Geology and Planetary Science
Above the Curie temperature, a permanent magnet changes to a
paramagnet (meaning it loses its intrinsic magnetic field, but still
can have an induced magnetic field). For the Earth, the magnetic field
is not due to intrinsic magnetism of its solid iron core, it is due to
an induced magnetic field owing to convection of the liquid iron shell
around the solid core. Thus, the liquid shell of iron is the source --
not a barrier -- to the magnet field.
Hope this helps,
Earth?s magnetic field is not well understood. It appears to be created by electric currents in the conductive metallic core. So in essence it is an electromagnet, not an iron ferromagnet.
Richard E. Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
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