Static and high-frequency magnetic properties of Fe and Cr substituted lanthanum manganites

Studies aimed at the nature of magnetic interactions in Fe and Cr substitut ed lanthanum deficient manganites, La0.88Mn1-xFexO3 (x = 0-0.15) and La0.88 Mn1-yCryO3 (y = 0-0.175) are reported. The oxides order ferromagnetically f or the entire range of x- and y-values. A decrease in the Curie temperature T-c with increasing substitution is observed for both compounds, but the d ecrease in T-c is large for Fe substitution. A large decrease was also seen in the low-temperature magnetic moment of Fe substituted samples. The data indicate possible ferromagnetic ordering of Cr and antiferromagnetic order ing of Fe moments in the oxides. Ferromagnetic resonance studies indicate ( i) strong spin-lattice effects in the paramagnetic state, (ii) valence-exch ange effects in the ferromagnetic state, and (iii) possible microscopic inh omogeneities in Cr-substituted samples (C) 2000 Elsevier Science B.V. All r ights reserved.