Just for the record, The text is Introduction to Electrodynamics (4th Edition) by David J. Griffiths Chap.6. What does "when the magnetic dipoles are aligned" mean? Does it mean Both moments are parallel to each other's magnetic field? i.e. ##m\times B = 0## for both? Or is it ##m_1\parallel m_2##? Judging from the context in the textbook, it seems to be the first one, but a previous section talking about ferromagnetics etc. seem to imply the second one.