Magnetic form factor of Cu in La2CuO

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 $Q=4$ ${\mathrm{\AA{}}}^{\ensuremath{-}1}$, although a plateau between 1 and 3 ${\mathrm{\AA{}}}^{\ensuremath{-}1}$ 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 ${T}_{N}\ensuremath{\simeq}185$ K with an average ordered moment $\ensuremath{\mu}=0.30{\ensuremath{\mu}}_{B}$ per Cu atom.