Solid State Physics - Physics Previous Year Questions

A ferromagnetic mixture of iron and copper having 75% atoms of Fe exhibits a saturation magnetization of \( 1.3 \times 10^6 \) A m\(^{-1}\). Assume that the total number of atoms per unit volume is \( 8 \times 10^{28} \) m\(^{-3}\). The magnetic moment of an iron atom, in terms of the Bohr Magneton, is

The total energy of an ionic solid is given by an expression $E = -\frac{\alpha e^2}{4\pi\epsilon_0 r} + \frac{B}{r^n}$ where $\alpha$ is Madelung constant, $r$ is the distance between the nearest neighbours in the crystal and $B$ is a constant. If $r_0$ is the equilibrium separation between the nearest neighbours then the value of $B$ is