Dia/Para/Ferromagnetism
Materials in B-field. Builds on Lorentz Force.
In 2000, physicists at the Radboud University in the Netherlands placed a live frog inside a 16-tesla magnetic field (about 300,000 times Earth’s field). The frog floated in mid-air, perfectly levitated.
Why does a living frog levitate in a strong magnetic field?
The frog levitates because water is diamagnetic! Every water molecule, when placed in a magnetic field, develops a tiny opposing magnetic moment. This creates a weak repulsive force. In a powerful 16T magnet with a strong field gradient, this repulsion becomes strong enough to overcome gravity. The frog is essentially floating on an invisible cushion of magnetic repulsion — every molecule in its body pushes back against the field.
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Drag different materials into the magnetic field region. Watch how diamagnetic materials are repelled, paramagnetic materials are weakly attracted, and ferromagnetic materials are strongly attracted. See the atomic dipoles respond in real time!
M = χₘH
Susceptibility χ is negative for diamagnets (opposing), tiny positive for paramagnets (weakly aligning), and huge positive for ferromagnets (strongly aligning). Every material in the universe is at least diamagnetic.
Andre Geim won the 2000 Ig Nobel Prize for levitating a frog. He later won the 2010 REAL Nobel Prize for graphene — making him the only person to have won both.
Permanent magnets are ferromagnetic — their domains remain aligned even without an external field. Heat them above the Curie temperature and they become paramagnetic, losing their permanent magnetism.
When lava cools past the Curie temperature, its ferromagnetic minerals “freeze” in the direction of Earth’s field. This creates a permanent record of Earth’s magnetic field reversals in ocean floor rocks.
Pyrolytic graphite is so strongly diamagnetic that small pieces can visibly levitate above an array of permanent magnets at room temperature — no superconductors needed!
“Everything is magnetic. Diamagnets push back. Paramagnets lean in. Ferromagnets snap on. With a strong enough field, you can levitate a frog, a strawberry, or a grasshopper. Andre Geim proved it — and then won a Nobel Prize for something completely different.”
Magnetism Explorer
Drag different materials into a magnetic field and see how they respond. Compare the three types of magnetism: diamagnetic, paramagnetic, and ferromagnetic. Adjust the field strength and watch the atomic dipoles respond in real time.
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Start by dragging bismuth (strongly diamagnetic) into the field — it gets pushed out. Now try aluminum (paramagnetic) — it’s pulled in weakly. Finally, try iron (ferromagnetic) — it snaps into the field. Increase B and see how the force on each material scales differently. Switch to the domain view to see how ferromagnetic domains grow and align. Try “heating” the iron past its Curie temperature and watch it become paramagnetic!
Diamagnetism is universal — all matter has it. Paramagnetism and ferromagnetism are special properties of materials with unpaired electrons. The key distinction: in diamagnets, induced moments oppose the field. In paramagnets and ferromagnets, permanent moments align with the field. Ferromagnets are special because their moments interact with each other to form aligned domains.