Revisiting the magnetic structure and charge ordering in La1/3Sr2/3FeO3 by neutron powder diffraction and Mössbauer spectroscopy

Abstract

The magnetic ordering of La 1/3 Sr 2/3 FeO 3 perovskite has been studied by neutron powder diffraction and 57 Fe Mössbauer spectroscopy down to 2 K. From symmetry analysis, a chiral helical model and a collinear model are proposed to describe the magnetic structure. Both are commensurate, with propagation vector k = (0,0,1) in R3c space group. In the former model, the magnetic moments of Fe adopt the magnetic space group P 3 2 21 and have helical and antiferromagnetic ordering propagating along the c axis. The model allows only a single Fe site, with a magnetic moment of 3.46(2)μ B at 2 K. In the latter model, the magnetic moments of iron ions adopt the magnetic space group C2/c or C2 /c and are aligned collinearly. The model allows the presence of two inequivalent Fe sites with magnetic moments of amplitude 3.26(3)μ B and 3.67(2)μ B , respectively. The neutron-diffraction pattern is equally well fitted by either model. The Mössbauer spectroscopy study suggests a single charge state Fe 3.66+ above the magnetic transition and a charge disproportionation into Fe (3.66−ζ )+ and Fe (3.66+2ζ )+ below the magnetic transition. The compatibility of the magnetic structure models with the Mössbauer spectroscopy results is discussed.

Structural properties of charge disproportionation and magnetic order in Sr2/3Ln1/3FeO3 (Ln=La, Pr, and Nd)

“…The refined data shows two nonequivalent Fe sites whose ordered magnetic moments are 2.52 and 3.27 μ B , values that are consistent with previous studies [9,37] and are at odd with the ones expected for Fe 5+ and Fe 3+ (3 and 5 μ B ) in a full CD. In the course of this research, a magnetic study on Sr 2/3 La 1/3 FeO 3 has recently been reported [43]. The results of this work are in agreement with our study showing similar conclusions about the possible magnetic groups for a collinear ordering of the Fe moments.…”

“…This CD qualitatively agrees with other techniques such as RXS and BVS but quantitatively is a bit higher maybe due to differences in the temperature dependence for δ 1 and δ 2 . In any case, this technique allows us to discard the occurrence of a full disproportionation in opposite to previous interpretations [19] but in agreement with recent reports [43].…”

“…Coupled to the structural transition, long-range AFM ordering is established [38,43] with a similar sixfold periodicity. Refined magnetic moments for the two nonequivalent Fe sites were obtained from neutron diffraction patterns and its ratio was confirmed by Mössbauer spectroscopy.…”

Complete phase diagram of Sr1–xLaxFeO3 with versatile magnetic and charge ordering

“…Furthermore, a neutron diffraction experiment has suggested that the helimagnetic spin structure with q = (1/6, 1/6, 1/6) in the pseudo-cubic cell can be eligible as well as the collinear spin structure. 15 It should be noted here that Ca 2/3 La 1/3 FeO 3 with A-site ordered perovskite structure has recently been found to show two types of spin/charge ordering as a function of temperature. 16,17 Whereas the spin/charge ordering at lower temperatures is the same as that of Sr 2/3 La 1/3 FeO 3 , the other at higher temperatures has charge ordering along [010] and helical spin structure with a propagation vector q = (1/3, 1/3, 1/3) on the pseudo-cubic unit cell.…”

Phase Transformations of Perovskite La0.64(Ba1−xCax)0.36FeO3−δ Investigated by Mechanical Spectroscopy

“…The ideal structure of perovskite oxides is cubic and typical structural variations from the cubic structure include rotation and tilting of the octahedra, [1] off-centering of the A and/or B cations, [2][3][4] distortion of the octahedra due to the Jahn-Teller effect, [5] and expansion/contraction of the BO 6 octahedral cages. [6] In recent years, perovskite La 1Àx Sr x FeO 3Àδ samples have been extensively investigated due to the fundamental metal-insulator transition [7][8][9][10] and applications of oxygen separation membranes, [11] gas sensors, [12] and cathode materials for solid oxide fuel cells. [13] As a comparison, many studies have been made on perovskite La 1Àx Ba x FeO 3Àδ samples.…”