Final answer:
Materials made of magnetic atoms may not be magnetic if their internal magnetic domains are randomly organized or weakly coupled. Ferromagnetic materials exhibit strong magnetism, while diamagnetic materials only show magnetism when exposed to an external magnetic field.
Step-by-step explanation:
Materials composed of magnetic atoms are not always magnetic due to the organization of their magnetic domains. In ferromagnetic materials such as iron, cobalt, nickel, and gadolinium, the atoms act like tiny magnets that can align within regions called domains. However, if the domains are randomly oriented, they can cancel each other out and the material won't exhibit external magnetism. A material's magnetic properties also depend on the strength of coupling among atoms; some materials are ferromagnetic only at lower temperatures due to weaker coupling. Conversely, in diamagnetic materials, there are no permanent magnetic dipoles; the only magnetic effect comes from induced dipoles that align opposite to an applied magnetic field.