Influence of the Change in Oxidation Number of Mn on Magnetic Properties of ${\rm BaTi}_{{1}-{x}}{\rm Mn}_{x}{\rm O}_{3}$

We prepared
${\rm BaTi}_{1-x}{\rm Mn}_{x}{\rm O}_{3}$
samples (
$x=0$
and 0.05) by standard solid-state reaction at 700
$^{\circ}{\rm C}$
and 900
$^{\circ}{\rm C}$
in an Ar ambient to change oxidation number of Mn dopants. The fabricated samples were then studied structural characterization and electronic structures by means of X-ray diffraction and absorption, and Raman scattering and electron-spin-resonance spectrometers. We found oxidation numbers
$2+$
and
$3+$
of Mn ions coexisting in
${\rm BaTi}_{1-x}{\rm Mn}_{x}{\rm O}_{3}$
with
$x=0.05$
, where the
${\rm Mn}^{2+}/{\rm Mn}^{3+}$
ratio is about one for the sample annealed at 700
$^{\circ}{\rm C}$
. These Mn ions prefer locating at the Ti site in the tetragonal
${\rm BaTiO}_{3}$
host lattice. In particular, there is a change in the oxidation number of
${\rm Mn}^{2+}\rightarrow{\rm Mn}^{3+}$
when the annealing temperature changes from 700
$^{\circ}{\rm C}$
to 900
$^{\circ}{\rm C}$
. Their magnetic properties are accordingly changed. Meanwhile, annealing pure
${\rm BaTiO}_{3}$
in an Ar ambient at 700
$^{\circ}{\rm C}$
and 900
$^{\circ}{\rm C}$
does not lead to ferromagnetic (FM) order; they are almost diamagnetic. With the obtained results, we believe that FM order in Mn-doped
${\rm BaTiO}_{3}$
annealed in an Ar ambient is associated with exchange interactions of
${\rm Mn}^{2+}$
ions mediated by oxygen vacancies rather than associated with
${\rm Mn}^{3+}$
ions.