Structural and magnetic properties of the single-layer manganese oxide La 1-x Sr 1+x MnO 4

Using x-ray and neutron scattering, we have studied the structural and magnetic properties of the single-layer manganite La{sub 1-x}Sr{sub 1+x}MnO{sub 4}(0{ =}0.45) doping. LaSrMnO{sub 4}(x=0) 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{sub 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 Neel order disappears above x{sub c}=0.115(10). The magnetic frustration is closely related to changes in the e{sub 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 'nanopatches' begin to form above x{approx}0.25. At high doping (x{>=}0.45), the ground state of La{sub 1-x}Sr{sub 1+x}MnO{sub 4} exhibits long-range superstructural order and a complex antiferromagnetic order, which differs frommore » 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 {epsilon} that depends linearly on the e{sub g} electron concentration: {epsilon}=2(1-x). On the other hand, the magnetic order remains commensurate, but loses its long-range coherence upon doping beyond x=0.50.« less