Magnetic and valent ion states in the real structure of magnetoresistive manganite-lanthanum perovskites

V.S.Abramov, V.P.Pashchenko, S.I.Khartsev, O.P.Cherenkov


A.A.Galkin Physico-Technical Institute, National Academy of Sciences of Ukraine, R.Luxembourg st.72, Donetsk, Ukraine

Received May 11, 1998

The influence of manganese-to-lanthanum ratio in manganite-lanthanum perovskites 1-xMn1+xO3 (0<=x<=0.4) on the lattice defectness, temperatures of the resistence maxima (Tm) and magnetoresistive effect (DELTA>R/R0) in ceramic samples have been studied. The real manganite-lanthanum perovskite structure has been shown to contain vacansies in both cationic and anionic sublattices. The defect concentration increases in parallel with x. The most probable magnetic and valent state of ions responsible for Tm have been determined theoretically under account for contributions of the spin and orbital moments of electron shells and of the nuclear spin moment. A correlation has been established between the crystal lattice defectness (V(c), V(a)), magnetic and valent states of ions, Tm and DELTA*R/R0. A satisfactory agreement has been found between experimental and theoretical Tm values in the model of the real imperfect perovskite structure containing vacancies in both cationic and anionic sublattices and manganese ions of different valencies in different magnetic and valent states.

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