A spin-only magnetic moment occurs when an electron rotates on its own axis and generates a magnetic field.

$\mathrm{\mu } = \sqrt{\mathrm{n} ( \mathrm{n} + 2 )}\mathrm{BM}$
Here, n is the number of unpaired electrons.
The unit for a spin-only magnetic moment is the Bohr magneton (BM).

$\left({\left[\mathrm{Mn}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{2+}\right.$

${\mathrm{Mn}}^{2+}=3{\mathrm{d}}^5$

$\mu =\sqrt{5(5+2)}=5.91\mathrm{BM}$