Magnetic form factor of Cu inLa2CuO4

Abstract

The magnetic form factor for Cu in a single crystal of the antiferromagnet ${\mathrm{La}}_2$Cu${\mathrm{O}}_4$ has been measured using neutron diffraction. The result is consistent with the calculation of Freeman and Watson for ${\mathrm{Cu}}^{2+}$ at least up to $Q=4\mathrm{}$ ${\mathrm{\AA }}^{-1\mathrm{}}$, although a plateau between 1 and 3 ${\mathrm{\AA }}^{-1\mathrm{}}$ suggests a small contribution of moment at the out-of-plane oxygen sites. For larger values of $Q$ the form factor for ${\mathrm{La}}_2$Cu${\mathrm{O}}_4$ drops faster than for ${\mathrm{Cu}}^{2+}$. The sample ordered antiferromagnetically at $T_N\simeq 185$ K with an average ordered moment $\mu =0.30\mathrm{}{\mu }_B$ per Cu atom.