Antiferromagnetic
Spin Correlations Between Corner-Shared [FeO<sub>5</sub>]<sup>7–</sup> and [FeO<sub>6</sub>]<sup>9–</sup> Units, in the Novel Iron-Based
Compound: BaYFeO<sub>4</sub>
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Abstract
A novel
quaternary compound in the Ba–Y–Fe-O phase diagram was
synthesized by solid-state reaction and its crystal structure was
characterized using powder X-ray diffraction. The crystal structure
of BaYFeO<sub>4</sub> consists of a unique arrangement of Fe<sup>3+</sup> magnetic ions, which is based on alternate corner-shared units of
[FeO<sub>5</sub>]<sup>7–</sup> square pyramids and [FeO<sub>6</sub>]<sup>9–</sup> octahedra. This results in the formation
of stairwise channels of FeO polyhedra along the <i>b</i> crystallographic axis. The structure is described in an orthorhombic
crystal system in the space group <i>Pnma</i> with lattice
parameters <i>a</i> = 13.14455(1) Å, <i>b</i> = 5.694960(5) Å, and <i>c</i> = 10.247630(9) Å.
The temperature-dependent magnetic susceptibility data reveal two
antiferromagnetic (AFM) transitions at 33 and 48 K. An upturn in the
magnetic susceptibility data above these transitions is observed,
which does not reach its maximum even at 390 K. The field-dependent
magnetization data at both 2 and 300 K show a nearly linear dependence
and do not exhibit significant hysteresis. Heat capacity measurements
between 2 and 200 K reveal only a broad anomaly without any indication
of long-range ordering. The latter data set is not in good agreement
with the magnetic susceptibility data, which makes it difficult to
exactly determine the magnetic ground state of BaYFeO<sub>4</sub>.
Accordingly, a temperature-dependent neutron diffraction study is
in order, which will enable resolving this issue. The theoretical
study of the relative strengths of magnetic exchange interactions
along various possible pathways, using extended Hückel spin
dimer analysis, shows that only interactions between square pyramidal
and octahedral centers are significant, and among them, the intrachannel
correlations are stronger than interchannel interactions. This is
the first physical property study in such a magnetic ion substructure