Magnetic interactions studies of Co and Ni-doped manganites using soft XMCD

An investigation of the electronic structure and magnetic moments of Co2+ a nd Ni2+ cations in doped CMR manganites Pr0.5Ca0.5(Mn1-xBx)O-3 (B = Co with x = 0.05 and B = Ni with x = 0.04) was realized using soft X-ray Absorptio n Spectroscopy (sXAS) and soft X-ray Magnetic Circular Dichroism (sXMCD) at Co, Ni and Mn L-2,L-3-edges. Compared to similar XAS experiments in Cr dop ed manganites, a smaller charge transfer character from Co or Ni 3d band to the oxygen 2p band is evidenced at low doping rate which suggest that Co a nd Ni ions would not participate directly in the double exchange phenomena contrary to Cr3+ ions. sXMCD showed that Co and Ni magnetic moments align parallel to the Mn magne tic moments, contrary to the Cr magnetic moment which was shown to align an tiparallel to the Mn sublattice in Cr doped samples. A simple phenomelogica l model, based on electronic phase segregations, is proposed to understand the nature of the magnetic interactions in the doped manganites. It shows t hat the physical properties induced by Co and Ni doping in manganites are n ot controlled by the same mechanism as in Cr doped manganites. (C) 2001 Els evier Science Ltd. All rights reserved.