17.1: Introduction to Magnetic Dipole Moments

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A number of different units for expressing magnetic dipole moment (hereafter simply “magnetic moment”) are commonly seen in the literature, including, for example, erg \(\text{G}^{-1}\), \(\text{G cm}^3\), \(\text{Oe}\) \(\text{cm}^3\), \(\text{T m}^3\), \(\text{A m}^2\), \(\text{J T}^{-1}\). It is not always obvious how to convert from one to another, nor is it obvious whether all quantities described as “magnetic moment” refer to the same physical concept or are dimensionally or numerically similar. It can be almost an impossibility, for example, to write down a list of the magnetic moments of the planets in order of increasing magnetic moment if one refers to the diverse literature in which the moments of each of the nine planets are quoted in different units. This chapter explores some of these aspects of magnetic moment.

In previous chapters, I have used the symbols \(p_e\) and \(p_m\) for electric and magnetic dipole moment. In this chapter I shall be concerned exclusively with magnetic moment, and so I shall dispense with the subscript m.