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Neutron powder diffraction study of the anion-deficient La_0.70Sr_0.30MnO_3.00-γ manganites

Sergei Trukhanov ¹, Aleksey Trukhanov ², Svetlana Zemskova ³, Anatoliy I. Beskrovniy ³, Henryk Szymczak ⁴

1. The Joint Institute of Solid State and Semiconductor Physics of NASB, P.Brovki str., 19, Minsk 220072, Belarus
2. Vitebsk State University (VSU), av. Moskovskaya 33, Vitebsk 210036, Belarus
3. Joint Institute for Nuclear Research, Dubna, Russian Federation
4. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland

Abstract

Using powder neutron diffraction method the magnetic structure of the anion-deficient solid solution La_0.70Sr_0.30MnO_3.00-γ (γ = 0.15; 0.20) at different temperatures has been determined. It is established that the magnetic structure changes with oxygen vacancies concentration. For the investigated samples the structural phase transitions have not been detected. The oxygen stoichiometric La_0.70Sr_0.30MnO_3.00 sample is ferromagnet with T_C ~ 360 K. At the T = 287 K the spontaneous magnetic moment is M_S = 2.92(5) µ_В / f. u., whereas at the T = 10 K – M_S = 3.53(6) µ_В / f. u. The direction of the total magnetic moment is along to [110]. For the anion-deficient La_0.70Sr_0.30MnO_2.85 sample the long-range magnetic ordering is absent for all the investigated temperatures. This sample is spin glass with the freezing temperature T_f ~ 45 K. For the anion-deficient La_0.70Sr_0.30MnO_2.80 sample is detected partial long-range antiferromagnetic ordering at the ~ 10 and ~ 40 K. At the T = 40 K the spontaneous magnetic moment is M_S = 0.83(3) µ_В / f. u., whereas at the T = 10 K – M_S = 0.88(1) µ_В / f. u. The direction of the antiferromagnetic exis is along to [111]. The obtained data confirm the theory of the magnetic phase state forming for the Sr-doped anion-deficient manganites. In according to this theory in case of orbital ordering absence the lowering of the coordination of the magnetic ion results to change of the indirect superexchange interactions Mn³⁺-O-Mn³⁺ sign from positive to negative. This work was partly supported by Belarus Fund for Basic Research (Project F06R-078).

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