Magnetic materials are classified by their susceptibility ($\chi$):

1. Diamagnetic: $\chi$ is small and negative. Repelled by fields.
2. Paramagnetic: $\chi$ is small and positive. Weakly attracted.
3. Ferromagnetic: $\chi$ is large and positive. Strongly magnetized in the direction of the field due to domain alignment. (e.g., Iron, Cobalt, Nickel).