Magnet manufacturing companies, for example Dexter Magnetic Technologies do not hesitate to explain the effects of heat upon magnets - citing how it degenerates the magnetic properties with levels of reversible and irreversible demagnetization.

However, they gloss over the "Why" of this phenomenon comparatively quickly.

From the link above they state that

Atoms have a nucleus around which spinning electrons orbit. As temperature increases (from absolute zero), the distance from the nucleus, and other electrons, increases so they follow a longer path and have less influence on each other, and magnetic properties of metallic magnets generally decrease.

Am I correct in understanding that : 1) The magnetic properties we see in magnets are due to the net orientation of magnetic spins of electrons. 2) The distance of an electron to the nucleus dictates the influence of the overall randomness or alignment of the electrons in a material?

If these are correct, why does the distance of an electron to the nucleus have the effect of aligning the spins of other electrons?

If not, can someone please explain why exactly heat changes the overall magnetic properties of materials?

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    $\begingroup$ You picked a topic that takes an entire physics course to explain. :-) The explanation of the company is flat out wrong. The magnetic properties of magnets are related to the orientations of spins and the development of magnetic domains, i.e. small volumes in the material where the spins are almost parallel, but not necessarily pointing in the direction of other domains. The temperature dependence of the magnetization depends on the long range correlation between these domain... and calculating that is a very tough problem, see here for starters: en.wikipedia.org/wiki/Curie_temperature $\endgroup$ – CuriousOne Apr 15 '16 at 3:59
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    $\begingroup$ The magnetic properties of the electrons bounded in atoms are important and very relevant for the properties of the chemical elements. A hypothesis about the influence of the magnetic dipole moments of the electrons see here. $\endgroup$ – HolgerFiedler Apr 15 '16 at 4:28
  • $\begingroup$ Strong magnetic properties have Bose-Einstein-condensates. The absence of electromagnetic exchange processes allow the formation of magnetic structures. $\endgroup$ – HolgerFiedler Apr 15 '16 at 4:33

The company explanation is wrong, really except for the first sentence.

The correct hand waving explanation would be much longer.

Materials are composed of atoms which contain electrons, and electrons have intrinsic magnetic moments and specific orbitals around atoms that are not affected by temperature. The molecular bonds are affected at high temperatures.

Ordinarily, the enormous number of electrons in a material are arranged such that their magnetic moments (both orbital and intrinsic) cancel out. This is due, to some extent, to electrons combining into pairs with opposite intrinsic magnetic moments as a result of the Pauli exclusion principle (see electron configuration), or combining into filled subshells with zero net orbital motion. In both cases, the electron arrangement is so as to exactly cancel the magnetic moments from each electron. Moreover, even when the electron configuration is such that there are unpaired electrons and/or non-filled subshells, it is often the case that the various electrons in the solid will contribute magnetic moments that point in different, random directions, so that the material will not be magnetic.

However, sometimes—either spontaneously, or owing to an applied external magnetic field—each of the electron magnetic moments will be, on average, lined up. Then the material can produce a net total magnetic field, which can potentially be quite strong.

For magnetic materials, in the formation of the solid state of the atoms, there are small magnetic domains where the energetics are advantageous to building up a large magnetic moment from the collective moment of the electrons. These domains can be disturbed or even destroyed by heating, because heat affects the vibrational and rotational energies of the atoms and molecules in a lattice, and supply energy that will again randomize the directions of the magnetic moments.

For specific atoms, iron is the first discovered since ancient times, the term magnet comes from Magnesia a region in Greece where it was first discovered as magnesian stones. The creation of the "stones" from the cooling magma, gave them a collective magnetic moment and they became permanent magnets. Other solids can be manipulated with external magnetic fields so that their domain orientation generates a permanent magnetic field.

So heat can at first destroy the domain orientation which builds up the field,and then even the domains themselves if the material melts even partially.


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