Magnetic and crystallographic transitions in La(Fe_xV_1-x)O₃ perovskites

Full text: The aim of this investigation is to elucidate the complex magnetic behavior usually observed for LaVO₃ at low temperatures, particularly concerning to the anomalous diamagnetism, by introducing a nuclear probe (⁵⁷Fe) in the orthovanadate matrix. In this sense, the La(V_1-xFe_x)O₃ perovskites were synthesized by solid state reaction and/or by arc-melting the precursors oxides. The samples were characterized by X-ray diffraction, ⁵⁷Fe Mössbauer spectroscopy and magnetization techniques.The diffractometric analysis (Rietveld refinement) revealed that the samples crystallized mostly with orthorhombic structure (Pbnm space group) and that the lattice parameters of the pseudo-ternary compounds decrease linearly with the progressive substitution of iron by vanadium,in agreement with the Vegard's law. Evidence for a crystallographic transition occurring at ~130 K, to a monoclinic structure (P1121/a Space group) was observed. The magnetization curves showed the occurrence of anomalous magnetism in the vanadium richest samples, but this magnetic transition is hidden for samples rich in iron.It was also observed the reduction of the hyperfine magnetic field, which changes from a well defined sextet of 51,8 T, obtained at room temperature for LaFeO₃, to a magnetic field distribution and, further, to a paramagnetic component for the richest vanadium samples. Decreasing the temperature, the iron moments are eventually frozen for any vanadium concentration. Two magnetic sites composing some of the Mössbauer spectra corroborate the crystallographic transition undergone by the system. The magnetism of iron and vanadium cations are discussed in order to explain the whole magnetic behavior of this perovskite system. (author)