Five types: (1) Diamagnetic: all electrons paired, weakly repelled (NaCl, benzene). (2) Paramagnetic: unpaired electrons, weakly attracted, loses magnetism when field removed (O2, $Cu^{2+}$, $Fe^{3+}$). (3) Ferromagnetic: domains of aligned spins, strongly attracted, retains magnetism (Fe, Co, Ni, CrO2). Above Curie temperature, becomes paramagnetic. (4) Antiferromagnetic: equal antiparallel alignment, zero net moment (MnO, MnO2). (5) Ferrimagnetic: unequal antiparallel alignment, net moment (Fe3O4, ferrites). Above Curie temperature, becomes paramagnetic.