Comprehensive investigations into crystal structures, electrical and magnetic properties of the (Lal-,Ca,)MnO, (z = 0 f 0.6) solid solutions are performed. Two concentration magnetic phase transitions are found : antiferromagnetic-ferromagnetic with x = 0.14 and ferromagnetic (T, = 150 K)ferromagnetic (T, = 260 K) at f = 0.2. It is shown that the first of them is due to the crystal structure 0'-0 orthorhombic transition, the secondto the increase of ferromagnetic interaction at the expense of additional interaction through conduction electrons. A diagram of the magnetic states for (La1 -,Ca,)MnO, at z = 0 + 0.6 is given.
Magnetic properties of nonstoichiometric lanthanum manganite LaMnOj + A as a function of the Mn4+ concentration (from 0 to 27%) and temperature (from 77 to 300 K) are investigated. The Mn4+ ions concentration depends on the degree of oxidation 1. It MaHraHme jIaHTaHa @a3o~b1ii nepexoa @eppoMarHeTmK-napaMarHeTHK ~~O M C X O A H T
In the perovskite-type compounds ABOJ rhombohedral distortions of the ideal cubic lattice cell are the result of tilting of the regular BO, octahedra about the [l 1 11 axis. It has been shown (MEGAW, DARLINGTON;ALEKSANDROV et al.;MOREAU et al.; MICHEL et al. 1971) that in such rhombohedral perovskites the structure parameters, e.g. the interaxial angle arh or the hexagonal lattice parameters uH and cH are completely determined by the tilt angle w. In these works the geometrical relations between these structural parameters and the tilt angle w are reported:Equations (1) to (3) are valid only for the compounds with the R3M and R3C symmetry having the interaxial angle aIh < 60". The octahedron BO, tilting about the [ill] axis in these compounds results in pseudocubic lattice (Fig. 1) contraction along [Till, while its size along [11 11 does not change (cH remains constant, cH/uH is greater than fi).The geometrical relations (1) to (3) are invalid for the compounds with the R?C symmetry (~H / u H is less than fi) (MEGAW, DARLINGTON;MICHEL et al. 1972).To remove this discrepancy it was assumed by MEGAW, DARLINGTON that in these compounds in addition to the octahedron BO, tilting about the [111] axis their strain also takes place, causing the decrease of the cH parameter. However, the octahedron strain in the compounds with the R2C symmetry in tilting is scarcely probable, since in these compounds there occurs a series of structure phase transitions (from cubic to rhombohedral, to orthorhombic, to monoclinic) and a tetragonal symmetry at varying temperature e.g. in PrAlO, (BIRGENEAU et al.) due to reorientation of the regular octahedron tilting axis.The hexagonal lattice parameter cH decrease is also observed when tilting of the regular octahedron BO, occurs not about the [111] -but about the [TI11 axis (Fig. 1). In this case the pseudocubic lattice cell contracts along the [ill] axis, with its size along the [rill axis being constant and the ratio cH/uH is less than fi. The equations (1) to (3) for the compounds with the R3C symmetry takes the form :CH = 2 1/61 cos (11
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