A magical artefact is a device or artefact respectively that is powered with magic. It can be fuelled with alignment influenced magic and depending on the artefact may have varying results based upon the magic.
For instance, dungeon hearts are inherently magical and ridiculously expensive. The battle staves of Calarine, on the other hand, are merely enhancing magic about an order of magnitude but incredibly rare, since their land of origin is destroyed and the art to make them lost (with the possible exception fo the clergy of Crowned Death).
Furthermore it needs to be unique or otherwise rare. Is this not the case one may consider it merely a magical device.
A list of magical artefacts may be viewed via Category:Magical Artefact.