Verwey Transition under Oxygen Loading in RBaFe2O5+w (R=Nd and Sm)

Nanoscale Ordering in Oxygen Deficient Quintuple Perovskite Sm2-εBa3+εFe5O15-δ: Implication for Magnetism and Oxygen Stoichiometry

“…In oxygen deficient perovskites, the ordering of these cations in the form of layers is at the origin of attractive magnetic and magnetoresistance properties, as for example in LnBaCo 2 O 5+δ "112" cobaltites (see for a review ref [9]). In this respect, iron oxygen deficient perovskites, such as LnBaFe 3 O 8+δ [6,[10][11] and LnBaFe 2 O 5+δ [12][13][14][15], isostructural to the cobalt layered perovskites, have also attracted attention as examples of compounds with double ordering in the cationic sites Ba 2+ /Ln 3+ and in the anionic sites between oxygen and vacancies in the form of layers. Like the cobaltites, these layered ferrites exhibit attractive physical properties such as magnetoresistance and Verwey transition under oxygen loading.…”

Checkerboard to stripe charge ordering transition in TbBaFe2O5

“…Woodward et al explored this connection through a systematic study of RBaFe 2 O 5 (R = Ho, Dy, Tb, Gd, Eu, Sm, and Nd) [8][9][10][11][12] . For all compounds, a signature of another transition was observed above T V that is characterized by subtle anomalies in heat capacity, resistivity, magnetization, and changes in unit the unit cell volume.…”

: Extent of charge ordering by Mössbauer spectroscopy and high-intensity high-resolution powder diffraction

“…The recently synthesized [22] RBaFe 2 O 5 (R ¼ rare-earth atom) is the hitherto only such phase of the non-tilted perovskite type. It exhibits all symptoms of the Verwey transition: conductivity change by two orders of magnitude [23,24], thermal effect [25,26], change in unit-cell volume and deformation [25], first-order transition [25]. The same features are shown by high-quality Fe 3 O 4 : conductivity [27], thermal effect [16], volume change [28], first-order transition [29].…”

“…This disproportionation is facilitated by the small orthorhombic distortion that is present in the structure below the Ne´el temperature T N ¼ 420 K [34]. No powder diffraction technique is able to detect any long-range order for this partial charge separation [23,33,34]. At a somewhat lower temperature T V ¼ 210-310 K, depending on R [26], the second chargeordering step has the major symptoms of the first-order Verwey transition.…”

“…In RBaFe 2 O 5 at high temperatures, valence-mixed Fe 2:5þ state is formed [31] whereas, at low temperatures, Mo¨ssbauer spectroscopy [25,31], synchrotron X-ray powder diffraction (SXPD) [23,25,26,32] and neutron powder diffraction (NPD) [23,25,33,34] reveal signs of a two-step charge separation and ordering. The first step is weaker and in several aspects premonitory to what happens at the second step.…”