Synthesis and Characterization of MnCrO4, a New Mixed-Valence Antiferromagnetстатья

Статья опубликована в высокорейтинговом журнале

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Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 4 февраля 2014 г.

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[1] Synthesis and characterization of mncro4, a new mixed-valence antiferromagnet / V. B. Nalbandyan, E. A. Zvereva, G. E. Yalovega et al. // Inorganic Chemistry. — 2013. — Vol. 52, no. 20. — P. 11850–11858. A new orthorhombic phase, MnCrO4, isostructural with MCrO4 (M = Mg, Co, Ni, Cu, Cd) was prepared by evaporation of an aqueous solution, (NH4)2Cr2O7 + 2 Mn(NO3)2, followed by calcination at 400 oC. 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 MnCrO4 phase where both cations are octahedral, the new phase contains Cr in a tetrahedral environment suggesting the charge balance Mn2+Cr6+O4. 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 TN ≈ 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 TN. MnCrO4 is a semiconductor with activation energy of 0.27 eV; it loses oxygen on heating above 400 oC to form first Cr2O3 plus Mn3O4 and then Mn1.5Cr1.5O4 spinel. [ DOI ]

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