Physical properties and magnetic structure of the layered oxyselenideLa2O3Mn2Se2

Abstract

We report the characterization of the layered rare-earth manganese oxyselenide La 2 O 3 Mn 2 Se 2 . The susceptibility data show a broad maximum near 350 K, indicating the existence of two-dimensional ͑2D͒ short-range ordering in this compound. A sharp feature associated with a short-range to long-range antiferromagnetic phase transition is seen at 163 K. A very small heat-capacity anomaly is detected around 163 K, indicating that most of the magnetic entropy is lost during the 2D ordering process. Both crystal and magnetic structures were studied by neutron powder diffraction at 300, 200, 150, 100, and 6 K. The structure was refined in space group I4 / mmm with a = 4.13 939͑3͒ Å and c = 18.8511͑2͒ Å at ambient temperature. No structural distortion was detected. The resulted magnetic structure is G-type with a propagation vector of k = ͑0,0,0͒ and an ordered magnetic moment of 4.147͑28͒ B / Mn along c is found at 6 K. Warren peak shape analysis of the neutrondiffraction data near 22°is employed to characterize the increase in correlation length in the 2D magnetic state on approaching the three-dimensional ordering transition.

Weak spin interactions in Mott insulating La2O2Fe2OSe2McCabe1, Stock2, Rodriguez3 et al. 2014Phys. Rev. B4527630View full textAdd to dashboardCite

“…The observation of a Warren peak characteristic of shortrange magnetic ordering only ∼14 K above T N (in contrast to ∼140 K above T N for La 2 O 2 Mn 2 OSe 2 ) [30] further supports the assignment of the (less frustrated) 2-k rather than the collinear model. This is because the 2-k structure diminishes the effects of J 1 and avoids frustration of J 2 and J 2 .…”

“…1(c)] can, to a first approximation, be described by the spin Hamiltonian involving single-ion anisotropies and Heisenberg terms with AFM J 1 and J 2 and FM J 2 , consistent with calculations [28] [27,30,41]. However, in the 2-k model, the J 1 interactions are unimportant as nearest-neighbor moments are perpendicular.…”

“…This agrees with the Ising-like character suggested to constrain M 2+ moments to lie along perpendicular local axes within the ab plane for M = Fe, Co (i.e., along Fe-O bonds in La 2 O 2 Fe 2 OSe 2 ). This anisotropy is not found in the high-spin M = Mn 2+ for which orbital angular momentum is zero and moments are oriented out of the ab plane [27,30]. This anisotropy overrides J 1 and with FM J 2 and AFM J 2 , favors the 2-k over the collinear model.…”

“…The magnetic Bragg reflections observed for La 2 O 2 Fe 2 OSe 2 are anisotropically broadened similarly to Sr 2 F 2 Fe 2 OS 2 , suggesting that both have similar magnetic microstructures. This peak broadening can be described by an expression for antiphase boundaries perpendicular to the c axis [29] [27,30,31].…”

Crystal structure and magnetic modulation in β−Ce2O2FeSe2

“…In these materials crystalline electric field anisotropy leads to a preference for Fe moments along Fe-O bonds [46] and moments are ordered ferromagnetically along each edge-shared chains [consistent with GoodenoughKanamori-Anderson (GKA) predictions]. The exchange constants are, however, relatively weak and both Mn and Co analogs are found computationally and experimentally to violate GKA rules and have antiferromagnetic order along the chains [47][48][49]. In β-Ce 2 O 2 FeSe 2 the local magnetic structure is probably governed by strong Fe1-Se-Fe2 ∼165 • antiferromagnetic exchange within the edge-shared Fe1Se 4 O 2 /Fe2Se 4 double chains (see Fig.…”