Taking a guess based on background knowledge: assuming it is something like an iron nail, the material is already prone to "picking up" magnetism. By aligning it with the Earth's field, you are providing a weak magnetic order. By striking the bar, phonons propagate and allow a source for spin-flip interactions that allow the bar to pick up a weak ferromagnetic order, making itself magnetic.
>>7806223 my intuition was something similar, though i've never been comfortable with phonons. Having all that energy from the impulse must be enough to energize the electrons enough for them to have a chance to align their spins with the external field
>>7806247 Magnetism in ferrous materials is from ferromagnetic ordering of the atoms, not the electrons. In something like iron, the electrons you have meaningful access to aren't going to pick up ferromagnetic ordering terribly easily because they are rather free to move around and those at the Fermi level should barely register the hammer strike at all. So, you need some high energy phonons to go around and mediate the ferromagnetic ordering of the atomic nuclei.
>>7806289 Ferromagnetic ordering will require some sort of communication between the atoms. That communication in a crystalline structure is done largely through phonons since they are just quantized lattice vibrations and all.
>>7806276 So what I gathered is the impact, these were tiny 'natural magnets' like in a stereo speaker, it 'reset' the magnetic alignment of the magnetic-ferro pins. Like if you rub a threading needle on a magnet, it becomes temporarily magnetic, by whacking the magnet with a hammer, it temporarily becomes NOT magnetic, by 'resetting' the individual alignments of each atom. It'd be magnetic again in a few minutes.
>>7806352 Damn I would not have expected that. I'm 25 but I see /sci/ and generally think it's either really young kids trying to seem profound or it's people my age trying to seem like they didn't squander their lives already
>>7806289 Phonons are just atomic-scale mechanical vibrations. Because atoms have discrete energy levels and vibrational modes, if you look closely enough, sound waves in a material break down into quantized phonons, just like discrete energy levels cause light to break down into photons.
90% of the time, if you mentally replace "phonon" with "tiny jiggle", you'll still have a decently useful picture of what's going on.
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