Revisiting La2MMnO6 (M = Co, Ni, Cu, Zn) perovskites in view of 3d-electron configuration

Abstract

We investigate the impact of 3d-electron configuration on the magnetic and DC conductive properties of La2MMnO6 (M = Co, Ni, Cu, Zn) and offer evidence to an enhanced ionic ordering degree with the increase in the 3d electron number of an M ion. A key role of the 3d electronic configuration that influences the B-site ionic arrangement is revealed by changing both the ionic radii and bond covalency. The position of the valence band edge is shifted away from the Fermi level with the increase in 3d electrons, which reveals a strengthened electron localization behavior. Magnetic characterization indicates that the Co, Ni, and Zn samples present magnetic behaviors with half- and full-filled eg configurations, whereas the Cu sample shows a special Jahn-Teller configuration (t2g6eg3), giving rise to the degenerated eg states and significant change in bond parameters. Consequently, the Goodenough-Kanamori rules are not followed and the ferromagnetic coupling is weakened greatly. Further, DC resistivity measurements of samples M = Co, Ni, and Zn present thermally activated conductive behavior, in good accordance with the position shift of valence band edge. However, due to the Jahn-Teller effect arising from Cu2+ ion, a strong electron-phonon coupling is evidenced. This effect provides a suitable hopping channel for small polarons resulting in a considerable rise of its conductivity. Such changes in magnetization and DC conductivity of La2MMnO6 perovskites by modulating the M elements would inspire us to develop novel spin-electronic devices.