The conversation between human and AI assistant.
[|Human|] Given a reference text about magnetism, tell me the definition of magnetism and how magnetic materials are classified.
[|AI|] Magnetism is defined as the physical attributes that are mediated by a magnetic field, which is the capacity to induce attractive and repulsive forces. Magnetic materials are classified by their bulk susceptibility.
[|Human|] 
Given a reference text about magnetism, tell me the definition of magnetism and how magnetic materials are classified.