Physics, Astronomy & Cosmology / Re: Where is the gravitational potential energy? School-level question.« on: 31/12/2022 16:43:57 »
‘How to be a magnet’. It depends on the size of ferromagnetic and it’s crystal domain alignment.
In a half-field shell electrons are not paired and their tiny magnets are pointing in the same direction. This is intrinsic magnetism of electrons.
But if an atom is magnetic, it doesn’t need that the material made of lots of these atoms are magnetic.
Crystals. Ferromagnetic - a bunch of atoms are aligned in the same magnetic direction. Aligned domains (bunches of bunches) of atoms. This is a quantum property - aligned to macro size.
Domains of material can point in different directions.
Piece of iron may not have a magnetic field at all, because all domains are pointing to different directions.
However if you apply a strong magnetic field from outside the material, you can make one solid unified piece of magnet.
Magnetism is a quantum property magnified to the size of the object.
These criteria are difficult to fulfill. There are few materials that can do that: Fe, Co, Ni, Gd.
The magnetization of a magnetized material is the local value of its magnetic moment per unit volume, usually denoted M, with units A/m. A good bar magnet may have a magnetic moment of magnitude 0.1 A·m2 and a volume of 1 cm3, or 1×10−6 m3, and therefore an average magnetization magnitude is 100,000 A/m. Iron can have a magnetization of around a million amperes per meter.
Thanks for the link. But this rule does not always work. In our university laboratory, we used a press to draw stainless steel. After this process, part of the material was magnetized, and part was not. I can not understand how the material properties could change so much.
It depends on the steel grade. Google the article Behavior of steel as a living organism. There this phenomenon was described. My university supervisor was one of the co-authors of the article. Using plagiarism checker for students https://fixgerald.com/plagiarism-checker-for-students I took some of the material for my term paper. So it might be useful for someone else. Interesting analytics and research.