2 research outputs found
Synthesis and Characterization of MnCrO<sub>4</sub>, a New Mixed-Valence Antiferromagnet
A new orthorhombic phase, MnCrO<sub>4</sub>, isostructural with MCrO<sub>4</sub> (M = Mg, Co, Ni, Cu,
Cd) was prepared by evaporation of an aqueous solution, (NH<sub>4</sub>)<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> + 2 MnÂ(NO<sub>3</sub>)<sub>2</sub>, followed by calcination at 400 °C. It is characterized
by redox titration, Rietveld analysis of the X-ray diffraction pattern,
Cr K edge and Mn K edge XANES, ESR, magnetic susceptibility, specific
heat and resistivity measurements. In contrast to the high-pressure
MnCrO<sub>4</sub> phase where both cations are octahedral, the new
phase contains Cr in a tetrahedral environment suggesting the charge
balance Mn<sup>2+</sup>Cr<sup>6+</sup>O<sub>4</sub>. However, the
positions of both X-ray absorption K edges, the bond lengths and the
ESR data suggest the occurrence of some mixed-valence character in
which the mean oxidation state of Mn is higher than 2 and that of
Cr is lower than 6. Both the magnetic susceptibility and the specific
heat data indicate an onset of a three-dimensional antiferromagnetic
order at <i>T</i><sub>N</sub> ≈ 42 K, which was confirmed
also by calculating the spin exchange interactions on the basis of
first principles density functional calculations. Dynamic magnetic
studies (ESR) corroborate this scenario and indicate appreciable short-range
correlations at temperatures far above <i>T</i><sub>N</sub>. MnCrO<sub>4</sub> is a semiconductor with activation energy of
0.27 eV; it loses oxygen on heating above 400 °C to form first
Cr<sub>2</sub>O<sub>3</sub> plus Mn<sub>3</sub>O<sub>4</sub> and then
Mn<sub>1.5</sub>Cr<sub>1.5</sub>O<sub>4</sub> spinel
Synthesis and Characterization of MnCrO<sub>4</sub>, a New Mixed-Valence Antiferromagnet
A new orthorhombic phase, MnCrO<sub>4</sub>, isostructural with MCrO<sub>4</sub> (M = Mg, Co, Ni, Cu,
Cd) was prepared by evaporation of an aqueous solution, (NH<sub>4</sub>)<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> + 2 MnÂ(NO<sub>3</sub>)<sub>2</sub>, followed by calcination at 400 °C. It is characterized
by redox titration, Rietveld analysis of the X-ray diffraction pattern,
Cr K edge and Mn K edge XANES, ESR, magnetic susceptibility, specific
heat and resistivity measurements. In contrast to the high-pressure
MnCrO<sub>4</sub> phase where both cations are octahedral, the new
phase contains Cr in a tetrahedral environment suggesting the charge
balance Mn<sup>2+</sup>Cr<sup>6+</sup>O<sub>4</sub>. However, the
positions of both X-ray absorption K edges, the bond lengths and the
ESR data suggest the occurrence of some mixed-valence character in
which the mean oxidation state of Mn is higher than 2 and that of
Cr is lower than 6. Both the magnetic susceptibility and the specific
heat data indicate an onset of a three-dimensional antiferromagnetic
order at <i>T</i><sub>N</sub> ≈ 42 K, which was confirmed
also by calculating the spin exchange interactions on the basis of
first principles density functional calculations. Dynamic magnetic
studies (ESR) corroborate this scenario and indicate appreciable short-range
correlations at temperatures far above <i>T</i><sub>N</sub>. MnCrO<sub>4</sub> is a semiconductor with activation energy of
0.27 eV; it loses oxygen on heating above 400 °C to form first
Cr<sub>2</sub>O<sub>3</sub> plus Mn<sub>3</sub>O<sub>4</sub> and then
Mn<sub>1.5</sub>Cr<sub>1.5</sub>O<sub>4</sub> spinel