In a magnetic material, the energy of the exchange interaction between neighboring atoms is about 1 eV/atom, whereas the magnetic dipolar interaction between neighbouring assemblies of atoms has an average value of 10 ⁻⁵ eV/atom. Use this data to estimate the maximum size of a spherical single domain particle. ( Hint : Assume that the exchange interaction only operates between atomic neighbors, whereas in a small particle the dipolar interaction affects all atoms equally. In addition, for an estimate, assume that the atoms are cubes with a width of 0.2 nm).