How can we derive the following formula  $$\vec{B}(\vec{r})=\frac{\mu_0}{4\pi}\left[ \frac{3(\vec{m}\cdot\vec{r})\vec{r}}{r^5} - \frac{\vec{m}}{r^3}\right]\; ,$$ I want to derive it as limit of a pair of magnetic charges as the source shrinks to a point while keeping the magnetic moment $m$ constant. I know that it can also be derived as the limit of current loop, but here we have to use the vector potential  $$\vec{A}(\vec{r}) = \frac{\mu_0}{4 \pi}\frac{\vec{m} \times \vec{r}}{r^3} \;$$ and to be honest I don't really know what that actually is and where does it come form. So I would like to derive it using pair of magnetic charges. Thank you! I tried to find some online sources with this type of derivation, but no luck. (urls would be appreciated)

How can we derive the following formula:

$$\vec{B}(\vec{r})=\frac{\mu_0}{4\pi}\left[ \frac{3(\vec{m}\cdot\vec{r})\vec{r}}{r^5} - \frac{\vec{m}}{r^3}\right]\; ,$$ 

I want to derive it as a limit of a pair of magnetic charges, as the source shrinks to a point, while keeping the magnetic moment $m$ constant. I know that it can also be derived as the limit of a current loop, but here we have to use the vector potential:

$$\vec{A}(\vec{r}) = \frac{\mu_0}{4 \pi}\frac{\vec{m} \times \vec{r}}{r^3} \;$$ 

and to be honest I don't really know what that actually is, and where it comes from. So I would like to derive it using pair of magnetic charges. Thank you! 

I tried to find some online sources with this type of derivation, but no luck (urls would be appreciated).