TY - JOUR
T1 - Unexpected origin of magnetism in monoclinic Nb12O29 from first-principles calculations
AU - Fang, C. M.
AU - Van Huis, M. A.
AU - Xu, Q.
AU - Cava, R. J.
AU - Zandbergen, H. W.
N1 - Publisher Copyright: © The Royal Society of Chemistry 2015.
PY - 2015/1/21
Y1 - 2015/1/21
N2 - Nb12O29 is a 4d transition metal oxide that occurs in two forms with different symmetries, monoclinic (m) and orthorhombic (o). The monoclinic form has unusual magnetic properties; below a temperature of 12 K, it exhibits both metallic conductivity and antiferromagnetic ordering. Here, first-principles density-functional theory calculations are used to study the structure, relative stability and electronic properties of Nb12O29. The optimized crystal structures are in good agreement with experimental observations and total energy calculations show similar stability of the two phases, while a magnetic electronic state is slightly favoured for m-Nb12O29. The unusual magnetism of the monoclinic phase originates from a Stoner instability that can be attributed to the Nb atoms with valence states close to Nb5+, i.e., the atoms with an electronic configuration of ∼d0. This is in clear contradiction to current models in which the magnetism is attributed to the presence of localized Nb4+ ions with a formal d1 configuration. Our study demonstrates that in complex structures, magnetic properties are best not inferred from ionic models, but require a full quantum mechanical calculation over the whole unit cell.
AB - Nb12O29 is a 4d transition metal oxide that occurs in two forms with different symmetries, monoclinic (m) and orthorhombic (o). The monoclinic form has unusual magnetic properties; below a temperature of 12 K, it exhibits both metallic conductivity and antiferromagnetic ordering. Here, first-principles density-functional theory calculations are used to study the structure, relative stability and electronic properties of Nb12O29. The optimized crystal structures are in good agreement with experimental observations and total energy calculations show similar stability of the two phases, while a magnetic electronic state is slightly favoured for m-Nb12O29. The unusual magnetism of the monoclinic phase originates from a Stoner instability that can be attributed to the Nb atoms with valence states close to Nb5+, i.e., the atoms with an electronic configuration of ∼d0. This is in clear contradiction to current models in which the magnetism is attributed to the presence of localized Nb4+ ions with a formal d1 configuration. Our study demonstrates that in complex structures, magnetic properties are best not inferred from ionic models, but require a full quantum mechanical calculation over the whole unit cell.
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U2 - https://doi.org/10.1039/c4tc02222j
DO - https://doi.org/10.1039/c4tc02222j
M3 - Article
SN - 2050-7534
VL - 3
SP - 651
EP - 657
JO - Journal of Materials Chemistry C
JF - Journal of Materials Chemistry C
IS - 3
ER -