For electric dipole: The direction of the dipole moment is from negative to positive charge, but that of the electrostatic field is from positive to negative. But in the case of magnetostatics, the magnetic field and dipole moment have the same direction. Isn't that a bit strange? Or am I missing something?
[Physics] Direction of electric dipole moment and magnetic dipole moment
dipole-momentelectrostaticsmagnetostatics
Best Answer
When we introduce the idea of dipoles to students, we start off with macroscopic dipoles (like hand-sized bar magnets) for pedagogical reasons. In both the electric and magnetic cases, the dipole moment has an electromagnetic piece and some physical size: charge times length for the electric dipole, and current times area for the magnetic dipole. Your question here is about the interior field of the dipoles, where the distance from the center of the dipole to the point of interest is less than the length scale of the dipole.
However, outside of teaching examples, the region of interest for a dipole field is usually the "far-field" region, where the distance from the center of the dipole to the point of interest is much larger than the length scale of the dipole. In this limit the two dipole fields really are the same: there's a field along the axis of the dipole moment that is parallel to the dipole moment vector, and a slightly weaker return field In the equatorial region, and both of these fields vary like $r^{-3}$ as the distance $r$ from the dipole varies.
In short: yes, there's a tiny region in the interior of an electric dipole where the field points the "wrong" way. But if you are close enough to the charge distribution that you care about this detail, then the dipole approximation is not the tool that you need to solve your problem.