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Electronic tuning of two metals and colossal magnetoresistances in EuWO1+ xN2- x perovskites
journal contributionposted on 24.04.2015, 14:49 by Minghui Yang, Judith Oro-Sole, Anna Kusmartseva, Alba Fuertes, J. Paul Attfield
A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO1+xN 2-x. Ammonolysis of Eu2W2O9 yields scheelite-type intermediates EuWO4-yNy with a very small degree of nitride substitution (y = 0.04) and then EuWO1+xN 2-x perovskites that show a wide range of compositions -0.16 < x < 0.46. The cubic lattice parameter varies linearly with x, but electron microscopy reveals a tetragonal superstructure. The previously unobserved x < 0 regime corresponds to oxidation of Eu (hole doping of the Eu:4f band), whereas x > 0 materials have chemical reduction of W (electron doping of the W:5d band). Hence, both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio. EuWO1+xN2-x phases order ferromagnetically at 12 K, and colossal magnetoresistances (CMR) are observed in the least doped (x = -0.04) sample. Distinct mechanisms for the hole and electron magnetotransport regimes are identified. © 2010 American Chemical Society.
This work was supported by the Ministerio de Ciencia e Innovacio´n (grants MAT2008-04587 and PR2008- 0164) and the Generalitat de Catalunya, Spain, and EPSRC, the Royal Society, EaStCHEM, and the Leverhulme Trust, U.K.