Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Internal-strain mediated coupling between polar Bi and magnetic Mn ions
  in the defect-free quadruple-perovskite BiMn$_3$Mn$_4$O$_{12}$   By means of neutron powder diffraction, we investigated the effect of the
polar Bi$^{3+}$ ion on the magnetic ordering of the Mn$^{3+}$ ions in
BiMn$_3$Mn$_4$O$_{12}$, the counterpart with \textit{quadruple} perovskite
structure of the \textit{simple} perovskite BiMnO$_3$. The data are consistent
with a \textit{noncentrosymmetric} spacegroup $Im$ which contrasts the
\textit{centrosymmetric} one $I2/m$ previously reported for the isovalent and
isomorphic compound LaMn$_3$Mn$_4$O$_{12}$, which gives evidence of a
Bi$^{3+}$-induced polarization of the lattice. At low temperature, the two
Mn$^{3+}$ sublattices of the $A'$ and $B$ sites order antiferromagnetically
(AFM) in an independent manner at 25 and 55 K, similarly to the case of
LaMn$_3$Mn$_4$O$_{12}$. However, both magnetic structures of
BiMn$_3$Mn$_4$O$_{12}$ radically differ from those of LaMn$_3$Mn$_4$O$_{12}$.
In BiMn$_3$Mn$_4$O$_{12}$ the moments $\textbf{M}_{A'}$ of the $A'$ sites form
an anti-body AFM structure, whilst the moments \textbf{M}$_{B}$ of the $B$
sites result from a large and \textit{uniform} modulation $\pm
\textbf{M}_{B,b}$ along the b-axis of the moments \textbf{M}$_{B,ac}$ in the
$ac$-plane. The modulation is strikingly correlated with the displacements of
the Mn$^{3+}$ ions induced by the Bi$^{3+}$ ions. Our analysis unveils a strong
magnetoelastic coupling between the internal strain created by the Bi$^{3+}$
ions and the moment of the Mn$^{3+}$ ions in the $B$ sites. This is ascribed to
the high symmetry of the oxygen sites and to the absence of oxygen defects, two
characteristics of quadruple perovskites not found in simple ones, which
prevent the release of the Bi$^{3+}$-induced strain through distortions or
disorder. This demonstrates the possibility of a large magnetoelectric coupling
in proper ferroelectrics and suggests a novel concept of internal strain
engineering for multiferroics design.

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The categories of this paper are: ao-sci
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The categories of this paper are: solv-int
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The categories of this paper are: hep-th
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The categories of this paper are: astro-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: q-fin
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The categories of this paper are: econ
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin
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The categories of this paper are: chem-ph
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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The categories of this paper are: eess
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The categories of this paper are: comp-gas
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The categories of this paper are: plasm-ph