The question is pretty much in the title. I've tried to google this but failed for the moment being.
I've tried to use a piece of aluminum foil as a torsion pendulum and hanged it below a stransparent plastic cup and put a strong magnet nearby. I expected it to get turned into the field like a bulk piece here but to my surprise it acts like a diamagnetic instead (turns out of the field). I wonder if surface aluminium oxide can cause this…
If you have any other hypotheses that explain this "failed" experiment, feel free to propose them.
Best Answer
Aluminium is paramagnetic and so an external magnetic field produced by a magnet would magnetise the aluminium such that the aluminium is attracted to the magnet.
However, even if the magnet field was a very strong one produced by a neodymium magnet, that force of attraction would be very small and you would have to set up the apparatus carefully to show the attraction.
What you probably have observed is the result of induced current produced in the aluminium which is in the presence of a changing magnet field produced by the movement of the magnet?
As the magnet approached the aluminium the magnetic field experienced by the aluminium would have increased and the aluminium would have reacted by trying to move into a region where the change of magnet field was smaller - further from the magnet.
This is Lena’s law in action where the induced current is in such a direction as to try and oppose the motion (changing magnetic field producing it).
So there is a force of repulsion between the magnet and the aluminium whilst they are moving towards one another.
If this is the reason for the effect that you have observed then you should observe a force of attraction as the magnet moves away from the aluminium. Do you?
Update after spotting the link to a video in the question.
Note how the suspended aluminium tube first orientates itself perpendicular to the magnetic field as the magnet is moved closer to the aluminium tube (the aluminium tube is trying to move into a region where the (change in ) magnetic field is smaller and then once the magnet stops moving the aluminium tube orientates itself parallel to the static magnet field showing aluminium to be paramagnetic.