Show that the low-field susceptibility, \(\chi_{0}\), of the spherical model at \(T
\[
\chi_{0} \approx\left(N \mu^{2} / k_{B} T\right) \cdot N m_{0}^{2}(T)
\]

where \(m_{0}(T)\) is the spontaneous magnetization of the system; note that in the thermodynamic limit the reduced susceptibility, \(k_{B} T \chi_{0} / N \mu^{2}\), is infinite at all \(T