magnetic body; magnetic substance
Technical term in physics and materials science for any material that exhibits magnetism.
Iron is a typical magnetic substance.
Motors are made using the properties of magnetic materials.
磁性 is the abstract property of magnetism, whereas 磁性体 refers to a concrete material or body possessing that property.
non-magnetic material; non-magnetic body
Compound of 磁性 (magnetism) + 体 (body, substance). A straightforward technical coinage.