title: Electronic tuning of two metals and colossal magnetoresistances in EuWO(1+x)N(2-x) perovskites.
abstract: A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO(1+x)N(2-x). Ammonolysis of Eu(2)W(2)O(9) yields scheelite-type intermediates EuWO(4-y)N(y) with a very small degree of nitride substitution (y = 0.04) and then EuWO(1+x)N(2-x) perovskites that show a wide range of compositions -0.16 <or= x <or= 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. EuWO(1+x)N(2-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.
authors.affiliation: Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh, EH9 3JZ, United Kingdom.
authors.forename: Minghui
authors.initials: M
authors.lastname: Yang
authors.forename: Judith
authors.initials: J
authors.lastname: Oró-Solé
authors.forename: Anna
authors.initials: A
authors.lastname: Kusmartseva
authors.forename: Amparo
authors.initials: A
authors.lastname: Fuertes
authors.forename: J Paul
authors.initials: JP
authors.lastname: Attfield