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Effect of Lattice Distortions on the Magnetic Behaviour of Perovskite‐Type Manganites
Author(s) -
Bokov V. A.,
Grigoryan N. A.,
Bryzhina M. F.,
Tikhonov V. V.
Publication year - 1968
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.19680280244
Subject(s) - antiferromagnetism , ferromagnetism , condensed matter physics , lattice (music) , ternary operation , crystallography , perovskite (structure) , magnetic moment , materials science , chemistry , physics , computer science , acoustics , programming language
Some series of solid solutions with perovskite‐type structure are synthesized and investigated, viz. the binary systems Nd 1− x , Me x MnO 3 where MeCa 2+ , Sr 2+ , Ba 2+ , and the ternary systems (Bi 1− x La x ) 0.5 Ca 0.5 MnO 3 and Bi 0.5 (Ca 1− x Me x ) 0.5 MnO 3 where MeSr 2+ , Pb 2+ , Ba 2+ . Distortions from the cubic perovskite structure are detected at room and liquid nitrogen temperature. Magnetic measurements are made in the temperature interval 77 to 800 ° K. For all the compounds, a correlation between lattice distortions and magnetic behaviour is observed; 1. cubic and slightly distorted compounds exhibits a pure ferromagnetism; 2. distortions from the cubic structure give reduced spontaneous moments and in some cases antiferromagnetism developes. The ferromagnetic nature of the Mn 3+ O 2− Mn 3+ and Mn 3+ O 2− Mn 4+ interactions which are found in the non‐distorted compounds is interpreted according to the Goodenough‐Kanamori rules assuming that the quasi‐static hypothesis is satisfied. The lattice distortions observed are thought to give rise to a static distortion in the Mn 3+ ion environment and an ordering of covalent bonds. As a result, some part of exchange couplings becomes antiferromagnetic. The influence of the decreased subtended angle in the MnO 2− Mn linkage is discussed. This angle decreases from 180 ° when the lattice becomes distorted and this fact disturbs the orbital orthogonality. This results in an increase of the antiferromagnetic t 2g −t 2g interaction via σ‐bonding and in the occurence of the other superexchange antiferromagnetic interactions which couple both the e g and t 2g orbitals and the t 2g and t 2g orbitals via π‐bonding. The contribution of double exchange to the ferromagnetism of mixed manganites is believed to be not important.