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| Home > Publications database > Correlation between structural and magnetic properties of La7/8Sr1/8Mn1-gammaO3 delta with controlled nonstoichiometry |
| Journal Article | PreJuSER-55241 |
; ; ; ; ; ;
2007
IOP Publ.
Bristol
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Please use a persistent id in citations: doi:10.1088/0953-8984/19/1/016003
Abstract: The structural and magnetic properties of air sintered and Ar and O-2 annealed La0.875Sr0.125Mn1-gamma O3+delta polycrystalline samples have been studied systematically. From the simultaneous refinement of room-temperature x-ray and neutron powder diffraction data, we have found that the crystal structure is orthorhombic (Pbnm, Z = 4; O) for the Ar annealed sample and rhombohedral 3c, Z = 2; R) for the air sintered and O2 annealed samples. At the O - R transition, the average Mn-O-Mn bond angle increases from 161.08(4)degrees. (Ar) to 163.38(1)degrees (O-2) and 163.64(1)degrees(air). Ar and O-2 annealings cause a decrease of the Curie temperature T-c from 240(1) K (air) via 237(1) K (O-2) to 192(1) K (Ar). The T-c is reduced by similar to 20% for the sample with O structure (Ar) as compared with that of the samples with R structure ( air and O2). The decrease of Tc is explained by the decrease of total strength of magnetic interactions, due to the decreased < Mn-O-Mn > bond angle and increased < Mn-O > bond length, and by the decrease of number of nearest magnetic neighbours. The possible reasons for the decrease of the Mn site occupancy after Ar and O-2 annealings and the sources of apparent excess oxygen are discussed. Thus we have shown that the actual distributions of cation vacancies in the A (La and Sr) and B (Mn) sublattices induced by the changes of Mn and oxygen contents through Ar and O2 annealings play an important role in the structural and magnetic properties. Comparing the Ar annealed with the air sintered sample, a decrease as small as similar to 2.2% of the relative oxygen content leads to a remarkably large (similar to 20%) effect on Tc.
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