Ferromagnetism and magnetoresistance in monolayered manganites Ca2-xLnxMnO4

Ferromagnetism (T-c) and negative magnetoresistive properties (maximum at 30 K) are observed in the monolayered manganites Ca(2 - x)Ln(x)MnO(4) (Ln = Pr, Sm, Gd, Ho and 0 < x less than or equal to 0.20) despite their pure bidimensional character. A detailed structural study was carried out using X-ray diffraction, electron diffraction, and high resolution electron microscopy. This shows that they exhibit an orthorhombic cell, with a approximate to b approximate to a(p)root 2, c approximate to 12 Angstrom and Aba2 or Abma as possible space groups. In all these oxides, (001)-type twinning is observed, on a unit cell scale,creating in this way a local periodicity of 24 Angstrom. In the x = 0.08 doped samples, it is observed that the microstructural state is strongly dependant on the synthesis process but it does not affect the magnetotransport properties.