Magnets stick to metals that are naturally attracted to them, known as ferromagnetic metals. These metals include iron, cobalt, steel, nickel, manganese, gadolinium, and lodestone. Some metals, such as rare-earth metals like samarium and neodymium, and alloys of iron, will maintain most of their magnetism even when they aren’t in a magnetic field, which is why they are known as magnetically hard and make good permanent magnets. Magnets will not stick to metals such as aluminum, copper, brass, lead, gold, and silver, as they are weak metals. However, properties including iron and steel can be added to these metals to make them magnetic. Magnets can also stick to non-metal objects that contain iron, such as rocks, and some plastics that have been infused with iron particles.