Nonuniform paramagnetic state in nonstoichiometric lanthanum manganites La1–xMn1–yO3

Resumo

The magnetic properties of nonstoichiometric lanthanum manganites La_1–xMn_1–yO₃ have been studied in the temperature range 80 K < T < 650 K. The Curie temperature T_C changes nonmonotonically as the number of Mn⁴⁺ ions increases. In the paramagnetic region, there exist isolated Mn ions and magnetic polarons which can be conserved to T ⩽ 4T_C, independent of the lattice symmetry. In the T_C < T < T_pol region, the temperature dependences of the magnetic susceptibility are nonlinear and can be described by the Curie law with a temperature-dependent Curie constant C. The sample has been prepared having a composition near the O′ → O structural transition; the spontaneous magnetization of the sample at T ⩽ 1.6T_C is associated to correlated polarons forming due to the double exchange in chains of the E-type antiferromagnetic phase.