Magnetic properties of anion deficit manganites Ln0.55Ba0.45MnO3-γ (Ln = La, Nd, Sm, Gd, γ ≤ 0.37)

A detailed study of oxygen deficit effect on magnetic properties was carried out for Ln(0.55)Ba(0.45)MnO(3-gamma) (Ln = La, Nd, Sm, Gd). It was shown that Ln(0.55)Ba(0.45) MnO3-gamma undergoes a concentrational phase transition from ferromagnetic to spin glass state at gamma = 0.15. The freezing temperature T-f decreases with decreasing oxygen content down to 80 K for gamma = 0.37. Another behavior has been revealed for Ln = Nd, Sm, Gd series; these compounds undergo a transition from ferromagnetic state (Ln = Nd) or spin-glass one(ln = Sm, Gd) into weak ferromagnetic state (gamma = 0.35) through intermediate antiferromagnetic state (gamma = 0.2). In contrast to stoichiometric manganites the Neel point increases from 136 K (Ln = Nd) to 160 K (Ln = Gd) with decreasing rare-earth ionic radii. It is supposed that both lanthanide and barium ions as well as oxygen vacancies are ordered in the strongly reduced rare-earth manganites. (C) 2000 Elsevier Science B.V. All rights reserved.