Observation of Spin Densities on Antibonding Orbitals in K2CuF4 by Neutron Diffuse Scattering

Direct observation of the spin densities on the F - -Cu 2+ -F - antibonding orbital in ferromagnetic K 2 CuF 4 was made by neutron paramagnetic diffuse scattering. The covalency effect appeared as an anomalous modification of the form factor of the Cu 2+ ions as suggested early by Hubbard and Marshall. The form factor at small angles was worked out precisely by the use of the intense critical scattering in the form of ridge reflecting the two-dimensional nature of this compound. As expected, a well behaved small peak appeared at lower scattering angles less than sin θ/λ∼0.1. The height of this peak as well as the flatness of the form factor at higher scattering angles were consistent to the NMR data and the theory.