Symmetry Origin of the Phase Transitions and Phase Separation in Manganites at Low Doping

Abstract

We analyze the symmetry changes of the paramagnetic to the A-type antiferromagnetic and to the ferromagnetic phase transitions in undoped and moderately doped LaMnO${}_3$, respectively. We show that in the orthorhombic-distorted perovskite manganites the phase separation at low doping is associated with the noncollinear nature of the magnetic orders permitted by symmetry. A simple model for the competition between the two phase transitions is put forward within the framework of Landau theory of phase transitions.

5 pages, 1 eps figure, Revtex, Phys. Rev. B60 Nov. 1999

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