paramagnetism
/ PARR-uh-MAG-net-ism /
Paramagnetism is a weak magnetism in which a material is faintly attracted into a magnetic field, but only while the field is present. Bring a strong magnet near liquid oxygen or a piece of aluminium and there is a slight pull, far too weak to feel with fridge magnets but real. It answers, why are many everyday materials slightly attracted to a strong magnet even though they are not 'magnetic' in the usual sense?
Paramagnetic materials are made of atoms that each carry a small permanent magnetic moment, but unlike in a ferromagnet these moments do not lock together; they point randomly in all directions and cancel out, so there is no magnetism on average. When an external field B is applied, it gently torques the moments toward alignment, and this partial alignment produces a weak net magnetisation in the same direction as B, giving a small attraction. Random thermal motion fights the alignment, so the effect gets weaker as temperature rises, a relationship captured by Curie's law, magnetisation proportional to B / T.
The key contrast is memory: a paramagnet aligns only while the field is on and forgets completely the instant the field is removed, so there is no permanent magnet. Paramagnetism is far weaker than ferromagnetism, typically thousands of times feebler, which is why we usually think of aluminium, oxygen, and platinum as 'nonmagnetic' even though they are, strictly, paramagnetic.
Liquid oxygen poured between the poles of a strong magnet visibly clings and bridges the gap: its molecules each carry a magnetic moment, and the field lines them up enough to hold on. Warm it up and the pull fades.
A weak, field-dependent attraction that vanishes the moment the field is removed.
Paramagnetism keeps no memory: remove the field and the magnetism vanishes at once, unlike a ferromagnet, which can stay magnetised. It is also far weaker, typically by a factor of thousands.