Ferrimagnetism as a Consequence of Unusual Cation Ordering in the Perovskite SrLa₂FeCoSbO₉

Abstract

A polycrystalline sample of SrLaFeCoSbO has been prepared in a solid-state reaction and studied by a combination of electron microscopy, magnetometry, Mössbauer spectroscopy, X-ray diffraction, and neutron diffraction. The compound adopts a monoclinic (space group P2/ n; a = 5.6218(6), b = 5.6221(6), c = 7.9440(8) Å, β = 90.050(7)° at 300 K) perovskite-like crystal structure with two crystallographically distinct six-coordinate sites. One of these sites is occupied by / Co, / Fe and the other by / Sb, / Fe. This pattern of cation ordering results in a transition to a ferrimagnetic phase at 215 K. The magnetic moments on nearest-neighbor, six-coordinate cations align in an antiparallel manner, and the presence of diamagnetic Sb on only one of the two sites results in a nonzero remanent magnetization of ∼1 μ per formula unit at 5 K.

CaLa2FeCoSbO9 and ALa2FeNiSbO9 (A = Ca, Sr, Ba): cation-ordered, inhomogeneous, ferrimagnetic perovskites

“…In general, taking into account also the homogeneity of the previously published SrLa2FeCoSbO9 [4], the cobalt-containing compounds are more homogeneous than the nickel-containing compounds, which could be related to the different reaction rates of Co 2+…”

“…We have previously reported the synthesis and characterisation of SrLa2FeCoSbO9, a perovskite-related compound that displays a novel cation-ordering pattern over the B-sites [4]. It adopts a monoclinic crystal structure with two crystallographically-distinct, sixcoordinate sites; one of these is occupied by ⅔ Co 2+ , ⅓ Fe 3+ and the other by ⅔ Sb 5+ , ⅓ Fe 3+ .…”

Structural and magnetic properties of the perovskites A2LaFe2SbO9 (A = Ca, Sr, Ba)

“…This study was originally motivated by the observation of relaxor ferromagnetism in La3Ni2SbO9 [17,18] and subsequently in La3Ni2TaO9 [16,36]. We have synthesised a number of triple perovskites containing Cr 3+ [20] and Fe 3+ [23,37] in an attempt to find more examples of relaxor behaviour but without success. In many cases, including those described above, we have invoked competition between NN and NNN interactions to explain the observed behaviour of our samples.…”