Electron-hole asymmetry in the rare-earth manganates: A comparative study of the hole- and the electron-doped materials

Properties of the hole-doped Ln(1-x)A(x)MnO(3) (Ln = rare earth, A = alkali ne earth, x < 0.5) are compared with those of the electron-doped compositio ns (x > 0.5). Charge ordering is the dominant interaction in the latter cla ss of manganates unlike ferromagnetism and metallicity in the hole-doped ma terials. Properties of charge-ordered (CO) compositions in the hole- and el ectron-doped regimes, Pr0.64Ca0.36MnO3 and Pr0.36Ca0.64MnO3, differ markedl y. Thus, the CO state in the hole-doped Pr0.64Ca0.36MnO3 is destroyed by ma gnetic fields and by substitution of Cr3+ or Ru4+ (3%) in the Mn site, whil e the CO state in the electron-doped Pr0.36Ca0.64MnO3 is essentially unaffe cted. It is not possible to induce long-range ferromagnetism in the electro n-doped manganates by increasing the Mn-O-Mn angles up to 165 and 180 degre es as in La0.33Ca0.33Sr0.34MnO3; application of magnetic fields and Cr/Ru s ubstitution (3%) do not result in long-range ferromagnetism and metallicity . Application of magnetic fields on the Cr/Ru-doped, electron-doped mangana tes also fails to induce metallicity. These unusual features of the electro n-doped manganates suggest that the electronic structure of these materials is likely to be entirely different from that of the hole-doped ones, as ve rified by first-principles linearized muffin-tin orbital calculations.