Why a Magnetic Field Can Tug Without Leaving a Magnet
Inside many atoms, electrons act like tiny magnetic needles because of their quantum properties, including spin. In a paramagnetic substance, some of those tiny moments can respond to an external field. The field slightly favors moments pointing along it, but the response is modest: random thermal jostling continually disrupts their alignment.
That competition explains why paramagnetism is weak. The field changes the odds for how moments point; it does not lock them into a shared direction. When the field is gone, there is no strong internal arrangement to preserve the effect.
The Difference Shows Up Where the Field Changes
A uniform magnetic field can produce a small magnetization, but a noticeable pull requires the field to vary across space. In a gradient, the stronger-field side exerts a greater influence, drawing paramagnetic material toward it. This is why the substance is attracted to a magnet rather than simply behaving like a tiny permanent magnet.
Oxygen offers a striking example. Its molecules have unpaired electrons, which give them paramagnetic behavior. In a sufficiently strong, nonuniform magnetic field, oxygen is drawn toward the stronger-field region. The same principle can help distinguish paramagnetic substances from materials that are not appreciably attracted.
The practical consequence is subtle but useful: a magnetic field can sort or move certain materials without leaving them magnetized afterward. Remove the field, and their weak response disappears.
