Magnetic properties of Nd-deficient manganites Nd0.9-xCaxMnOy

X-ray diffraction and magnetic studies of neodymium deficient Nd0.9-xCaxMnOy (0=<x=<0.4) systems have been carried out depending on oxygen or calcium content. The Nd0.9MnOy samples have been prepared in the 2.85=<y=<2.93 concentration range. According to differential thermal analysis (DTA) data the sample with y=2.85 exhibits a first-order phase transition at T=1200K, whereas in y=2.93 composition an anomaly of elastic properties evidences the transition nearby T=500K. The transitions are supposed to be caused by a cooperative ordering of eg-orbitals of manganese ions. Composition with y=2.85 is antiferromagnet with TN=85K, whereas for more oxidized Nd0.9MnOy samples a coexistence of antiferromagnetic and ferromagnetic phases is suggested. Low-temperature magnetic phase transition which is accompanied by a negative magnetization appearance has been found in the Nd0.9MnO2.90 compound. Magnetic behavior of Nd0.9-xCaxMnOy (0.1=<x=<0.4; 2.85=<y=<2.89) solids strongly resembles that observed for stoichiometric Nd1-xCaxMnO3 series. Properties of the Nd0.9-xCaxMnOy (0=<x=<0.4) solid solutions are in agreement with a hypothesis according to which a part of Nd ions can be substituted by Mn ions