  Trivalent americium has a non-magnetic ($J$ = 0) ground state arising from
the cancelation of the orbital and spin moments. However, magnetism can be
induced by a large molecular field if Am$^{3+}$ is embedded in a ferromagnetic
matrix. Using the technique of x-ray magnetic circular dichroism, we show that
this is the case in AmFe$_2$. Since $\langle J_z \rangle$ = 0, the spin
component is exactly twice as large as the orbital one, the total Am moment is
opposite to that of Fe, and the magnetic dipole operator $\langle T_{z}
\rangle$ can be determined directly; we discuss the progression of the latter
across the actinide series.
