Ab initio charge, spin and orbital energy scales in LaMnO ₃

Abstract

The first-principles SIC-LSD theory is utilized to study electronic, magnetic and orbital phenomena in LaMnO3. The correct ground state is found, which is antiferro orbitally ordered with the spin magnetic moments antiferromagnetically aligned. Jahn-Teller energies are found to be the largest energy scale. In addition it is the Jahn-Teller interaction which is the dominant effect in realising orbital order, and the electronic effects alone do not suffice.

Self-interaction correction in multiple scattering theory

“…This leads to a determination of the number of valence states and a nominal valence, as demonstrated by numerous calculations on rare earths, actinides, transition metal oxides, including the parent compounds of the high T c materials and the CMR materials. 3,4,5,6,7,8,9 The full SIC-LSD scheme is unfortunately difficult to implement. 10 This is due to the repeated transformations from reciprocal space (k-space) to real space to evaluate the self-interaction potential and the back transformations to k-space to solve the band structure problem.…”

Self-interaction-corrected relativistic theory of magnetic scattering of x rays: Application to praseodymium

“…For example a two-particle state composed of two single-particle states with m l = ± 1 has the same z component of orbital angular momentum as a two-particle state composed of two single-particle states with m l = ± 3, but Eq. (38) does not suggest that they will have the same scattering amplitude. Nonetheless, Blume's expression implies that a strong dependence of the cross section on the components of the magnetic moment is likely and indeed, this is exactly what we have found, an approximate, but by no means rigorous proportionality between orbital moment and magnitude of the cross section which is dependent on the polarization of the x ray.…”

“…For implementation purposes they must be described as many-electron states that will contain the index j which is being summed over in Eq. (38). In a magnetic material the radial part of the basis functions of the single particle wavefunctions, as well as the angular part, depend on m l .…”

“…Most interestingly, Eq. (38) implies that, with a suitable choice of the photon energy, geometry, and photon polarization it is possible to separate contributions to the cross section from the orbital and spin moments. However, this expression is not directly applicable in our resonant magnetic scattering studies because its derivation involves an approximation which is strictly not valid close to the resonance, while our approach is only valid around resonance because we ignore the negative energy contribution to the scattering amplitude, i.e., the terms that involve creation of virtual electron-positron pairs in the intermediate states in the second order perturbation theory (see Sec.…”

“…For these reasons and the fact that there is no one-to-one correspondence between the terms in our expression for the scattering amplitude and Blume's expression, there is no straightforward way to compare the two theories. It is often stated that Blume's expression (38) shows that the cross section for magnetic scattering will yield the orbital and spin moment of a material separately. Although this will usually be the case it is not rigorously true.…”