noun
magnetic body; magnetic substance
Technical term in physics and materials science for any material that exhibits magnetism.
鉄は代表的な磁性体です。
Iron is a typical magnetic substance.
磁性体の性質を利用して、モーターが作られています。
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.
Compound of 磁性 (magnetism) + 体 (body, substance). A straightforward technical coinage.