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It is written on wiki that "Permanent magnets are made from "hard" ferromagnetic materials..." Should I conclude from it that they are ferromagnetic? For its not written that they are ferromagnetic but that they are made from them. If they are not, then what are they? Diamagnetic? If they are ferromagnetic then there is a problem.

Ferromagnetic materials when kept in a magnetic field, their atoms or molecules arrange themselves so that their magnetic moment aligns with the magnetic field. Let us consider two bar magnets, very far from each other so that they don't interact, which are parallel in their polarity. Now suppose a uniform magnetic field so that for one magnet it is along its polarity and for the other, it is in opposite direction. If magnets are ferromagnetic then in both magnets the molecules will align themselves in the direction of the external field and since they are opposite for the magnets hence the direction of the magnetic moment will also become opposite in the two magnets. But polarity of magnets doesn't change with the external field, and hence magnets should not be ferromagnetic.

Is my reasoning correct?

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    $\begingroup$ Might be helpful - MAGNETS: How Do They Work? $\endgroup$
    – mmesser314
    Commented Mar 4, 2022 at 0:26
  • $\begingroup$ @mmesser314 I had seen this video and the other part of it 3-4 years ago. They are one of my favorite videos. $\endgroup$
    – Osmium
    Commented Mar 4, 2022 at 14:39

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...But polarity of magnets don't change with the external field...

How do you think they got magnetized in the first place?

..."hard" ferromagnetic materials.

The word "hard" means, high coercivity—the ability of a ferromagnet to resist changes in its magnetization.

You can change the strength and orientation of the "permanent" field of a permanent magnet if you subject it to a sufficiently strong external field—a field strong enough to overcome its coercivity.

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  • $\begingroup$ Thank you for your answer. Do you know some experiment in which reversing of the polarity of magnet is done? Thanks. $\endgroup$
    – Osmium
    Commented Mar 4, 2022 at 14:28
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    $\begingroup$ @Osmium, Do I know an experiment by name? No. If you wanted to do the experiment, the best approach probably would be to put the magnet inside a solenoid that could generate a strong enough field to overcome the material's coercivity. But note! Depending on what the magnet is made of, you may have to supply a non-trivial amount of power to the coil, and both the coil and the magnet may experience non-trivial forces. The experiment would have to be designed to withstand the heat and the forces. $\endgroup$
    – Solomon Slow
    Commented Mar 4, 2022 at 18:59
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    $\begingroup$ @Osmium, Google for "electromagnetic coin crusher" to see examples of home-built, magnetic apparatus with solenoids that are only good for one "shot" each because the magnetic field is so strong that the coil literally explodes. $\endgroup$
    – Solomon Slow
    Commented Mar 4, 2022 at 19:04

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