Magnetic form factor of Cu in La sub 2 CuO sub 4.

The magnetic form factor for Cu in a single crystal of the antiferromagnet La sub 2 CuO sub 4 has been measured using neutron diffraction. The result is consistent with Freeman and Watson's calculation for Cu sup (2+) at least up to Q=4angstroms sup (-1), although a plateau between 1 and 3angstroms sup (-1) suggests a small contribution of moment at the out-of- plane oxygen sites. For larger values of Q the form factor for La sub 2 CuO sub 4 drops faster than for Cu sup 2+. The sample ordered antiferromagnetically at T sub N ~ 185K with an average ordered moment mu = 0.30micron B per Cu atom.