Eli5 The earth has a magnetic field, including because of the metal core, but magnets are demagnetized at high temperature. How is this possible
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I saw something not too long ago where they were trying to show how the rotating core generated the magnetic field. But they couldn’t make it happen.
So I don’t know if they are certain this is the cause, and this is just an insufficient simulation, or if they just all thought it made sense and kind of accepted it as the best possibility and moved on because they couldn’t test it.
Magnetism and electricity are aspects of electromagnetism, the force and effects created by electric charges. Electric charge, mass, spin, etc., are basic properties of matter.
If you look at an immobile electric charge, you will see electrical effects from it. If you look at a moving electric charge, you will see magnetic and electric effects from it. And because motion is relative, you could be seeing purely electrical effects, whereas someone on a high speed train that’s passing by you could see magnetic effects from the charge you’re holding (immobile) in your hand.
Certain atoms have a magnetic field as a result of how the electrons (charges) orbit the nucleus inside the atom. If you have a material where these atoms “line up” their magnetic orientation / electron spin, then the material as a whole will have magnetic properties, the “added up” effects from all the individual atoms. Heat makes atoms vibrate with energy and in general they will rotate and reorient and their magnetism will be in a random direction and will cancel out rather than adding up.
Earth’s magnetic field, the Sun’s magnetic field, Jupiter’s, etc., all of these are created through different mechanisms, but they do all come down to the movement of charged particles inside the planet somewhere.
The earth isn’t a permanent magnet
Permanent magnets exist because all the atoms have their own tiny magnetic field and all those magnetic fields are all aligned, they add up to one large field, and are destroyed by heat because it gives each particle enough energy to randomly jiggle out of alignment with other atoms, so that all the atomic magnets cancel out
The earth on the other hand is a dynamo, basically the liquid metals in the mantle and core are all flowing, and that flow creates an electrical charge, and moving electric charges creates a magnetic field like one giant electromagnetic.
Oh this is a super cool question! You are indeed correct, bar magnets and those like it can not do hot temps, they fail. But that’s not how the Earth’s magnetic sphere operates. Here on the surface we often use stable magnets to generate electricity. This works on a principle that moving magnetic fields through each other creates electric current. But this is also true in reverse. Moving electric fields can cause magnetic fields.
So the Earth’s core is iron nickle… stuff, we’re not 100% but it’s metal and it’s solid and it’s hot AF. This basically only operates as an antenna. The outer core, however, is liquid and it moves, a lot, moving differently charged metals next to each other causes electricity to generate. And a side effect of generating electrical charge is you also create magnetic fields. This is then focused to the poles because of the axis of rotation and the rotation itself. The sciency name for this is called the “Dynamo Effect” which sounds like a stupid made up sci-fi hand wave, but that’s the name, they didn’t consult me when they named it.
But that’s the gist. The earth is basically accidentally a magnet, it’s a side effect of a geological process of having a liquid metal outer core that’s just hot enough and under just enough pressure for this to work.
Magnetic fields are generated by charged particles with angular momentum. Angular momentum comes from two different places.
1. Orbital angular momentum, which arises when a particle moves in a loop.
2. Spin angular momentum. This is a quantum property of particles which is intrinsic and depends on the kind of particle.
Permanent magnets (like cobalt) arise when all of the particles in a metal’s spin angular momentum line up with each other, creating a large net angular momentum and therefore magnetic field (dipole moment). When the temperature is high, all the spins jiggle around in random directions, and they cancel each other out, destroying the magnetism. The Earth does not work like this. It’s magnetic field arises because of orbital angular momentum – the Earth is spinning, as are all of the charged particles in the mantle, giving a large magnetic field.
The earths magnetic field isn’t created by the iron in the core being magnetic, it’s created by the way if flows around inside the core.
This has secondary effects or magnetising some of the iron, but let’s forget about this.
The mag Eric field is mostly from the movement of the iron.
Earth’s Outer Core is heated by the first events from the solar systems’ history, and by friction heating, caused by denser/colder material sinking to the bottom, and also by decay of radioactive isotopes. EOC also suffers from density variation throughtout its depth, denser stuff at the bottom, lighter on top. This sets up the conditions for an naturally occuring electric generator. Convection currents are transformed into electromagnetic ones by heating up the iron and electric currents are induced by earth’s magnetic field. Those electric currents have their own magnetic field. And thus the process is self sustained as long as there is heat being generated in large enough quantities.
The loss of magnetic properties is called the curie effect. The temperature at which it happens is called the curie point. Above the Curie temperature, the atoms are excited, and the spin orientations become randomized and that is what makes materials lose their magnetic properties. Minidisc is a magneto-optical media. Data gets recorded to it by using the curie effect.
The magnetic loss is not permanent. Once this cool down the magnetism returns.
Magnetism is caused my the movement of electrons, ie current. Every electron has a “magnetic moment”. An atom can have a net magnetic field due to the arrangement of its electrons as they orbit the nucleus. A group of atoms, ie a magnet, gets its net magnetic field from large percentages of its atoms having aligned magnetic fields. When a magnet like this is heated the atoms unalign which is why the magnet ceases to be a magnet at temperature.
The earths core is essentially spinning molten metal. Metals have a lot of electrons. Which means moving electrons. Which means current. Which means magnetic field.
Magnetism is a fancy word for magic.
Don’t believe me? If water is flowing from a mountain to level ground, why doesn’t it create an ‘aquatic field’ during flow? Because water, while remarkable, is not magic, of course.
So why is it that when electrons behave in, essentially, the same way – seeking equilibrium, that they generate fields of energy? Why is it that earth’s magnetic field doesn’t tear apart all matter on the planet, by ripping electrons to it’s positive pole, and all protons to the negative pole? Why doesn’t that happen when I stick my hand in a magnetic field? Well, because magnetism is magic, of course.
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