## Abstract

Using x-ray and neutron scattering, we have studied the structural and magnetic properties of the single-layer manganite La _{1-x}Sr _{1+x}MnO _{4}(0≤x<0.7). Single crystals were grown by the floating-zone method at 18 La/Sr concentrations. The low-temperature phase diagram can be understood by considering the strong coupling of the magnetic and orbital degrees of freedom, and it can be divided into three distinct regions: low (x<0.12), intermediate (0.12≤x<0.45), and high (x≥0.45) doping. LaSrMnO4U=O) is an antiferromagnetic Mott insulator, and its spin-wave spectrum is well described by linear spin-wave theory for the spin-2 square-lattice Heisenberg Hamiltonian with Ising anisotropy. Upon doping, as the e _{g} electron concentration (1-x) decreases, both the two-dimensional antiferromagnetic spin correlations in the paramagnetic phase and the low-temperature ordered moment decrease due to an increase of frustrating interactions, and Néel order disappears above x _{c}=0.115(10). The magnetic frustration is closely related to changes in the e _{g} orbital occupancies and the associated Jahn-Teller distortions. In the intermediate region, there exists neither long-range magnetic nor superstructural order. Short-range-correlated structural ́ nanopatcheś begin to form above x∼-0.25. At high doping (x≥0.45), the ground state of La _{1-x}Sr _{1+x}MnO _{4} exhibits long-range superstructural order and a complex antiferromagnetic order, which differs from that at low doping. The superstructural order is thought to arise from charge and orbital ordering on the Mn sites, and for x=0.50 we conclude that it is of B2mm symmetry. For x>0.50, the superstructural order becomes incommensurate with the lattice, with a modulation wave vector e _{g} that depends linearly on the eg electron concentration: eε=2(1-x). On the other hand, the magnetic order remains commensurate, but loses its long-range coherence upon doping beyond x=0.50.

Original language | English (US) |
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Article number | 024435 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 71 |

Issue number | 2 |

DOIs | |

State | Published - Jan 2005 |

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