Transport properties and magnetic behavior in the polycrystalline lanthanum-deficient manganate perovskites (≈La 1−xMnO 3)

• Published in: Materials research bulletin Vol. 32; no. 6; pp. 763 - 777
• Main Authors: Ferris, V., Goglio, G., Brohan, L., Joubert, O., Molinie, P., Ganne, M., Dordor, P.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.06.1997; Amsterdam Elsevier Science
• Subjects: A. magnetic materials; A. oxides; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conductivity of specific materials; D. electrical properties; D. magnetic properties; Electronic transport in condensed matter; Exact sciences and technology; Magnetic properties and materials; Nonmetallic ferromagnetic materials; Other crystalline inorganic semiconductors; Physics; Studies of specific magnetic materials; D. magnetic properties; D. electrical properties; A. magnetic materials; A. oxides; Stoichiometry; Inorganic compounds; Semiconductor materials; Magnetization; Phase transformations; Ternary compounds; Rhombohedral crystals; Lanthanum compounds; Transition element compounds; Spontaneous magnetization; Ferromagnetic materials; Rare earth compounds; Experimental study; Thermoelectric properties; Magnetic susceptibility; Manganates; Hopping; Remanent magnetization; Electric conductivity; Polarons
• ISSN: 0025-5408; 1873-4227
• DOI: 10.1016/S0025-5408(97)00044-5

The rhombohedral lanthanum manganates ≈La 1 − xMnO 3 (x = 0.0, 0.05, 0.1) were prepared by a soft chemistry route to test first as catalysts. These three weak ferromagnets exhibit a structural transition at T t slightly below T c. ≈La 0.9MnO 3 undergoes a group-subgroup R3̄c ↔ R3c transition most likely of second order. ≈LaMnO 3 does not show any insulator-to-metal transition, but does show a semiconductor-semiconductor at T t ~ 130 K. Analysis of the transport data (conductivity and thermopower) indicates hopping of polarons at both low and high temperature. An effective magnetic moment of 3.50 μ B / Mn is deduced from the spontaneous magnetization value at 5 K. The slight difference from the spin-only value (3.67 μ B ) is assigned to a spincanting effect which is reflected in the divergence of the FC and ZFC susceptibility curves at low fields (H ≤ 10 −2 T) and low temperature. Compared with recent results on thin films, the compositions x = 0.05, 0.1 are expected to show magnetoresistive effects as well as a semiconductor-to-metal transition. If it is verified on bulk samples which all contain a similar Mn 4+ content of 35%, the structural transition at T t could be considered as magnetically driven.