Synthesis, structure and magnetic properties of R–W–O–N (R=Nd and Eu) oxynitrides

Large magnetoresistances and non-Ohmic conductivity in EuWO1+xN2−x

“…2.88 and 2.68 Å, respectively, predicted from ionic radii of Eu 2+ and Eu 3+ ͒ but full determinations of the superstructure will be needed to obtain accurate distances. Magnetization measurements show that the three samples order ferromagnetically at 12 K, as observed in a previous study of an x = 0.58 sample, 5 with no variation in T C to within Ϯ0.5 K. Magnetization ͑M͒-field ͑H͒ loops ͓Fig. 1͑b͔͒ confirm the ferromagnetic order although the saturated moment of 4.1 B is significantly reduced from the theoretical value of 7 B for Eu 2+ , suggesting that spin canting or coexisting ferromagnetic and antiferromagnetic phases may be present, as discussed later.…”

“…2 Many oxide families are known to have such properties, but the utility of an unexplored class of materials-europium͑II͒ oxynitride perovskites-was recently demonstrated as colossal negative magnetoresistances ͑MRs͒ were discovered at low temperatures. 3 The presence of nitride enables d 0 transition metals in high formal oxidation states to be stabilized, e.g., Nb, 3 Ta, 3,4 and W. 5 Nitrogen-deficiency leads to electrondoping of the transition metal d-bands and the carrier transport may be strongly coupled to the magnetization from the Eu 2+ S =7/ 2 core spins, leading to −MRϾ 99% for EuNbO 2+x N 1−x ͑MR= ͓ ͑H͒ − ͑0͔͒ / ͑0͒; is resistivity, measured in zero field and magnetic field H͒. Here we report the magnetotransport properties of the correspondingly electron-doped material EuWO 1+x N 2−x , in which large negative MRs and microstructurally induced nonohmicity are discovered.…”

Ammonothermal Synthesis of the Mixed‐Valence Nitrogen‐Rich Europium Tantalum Ruddlesden‐Popper Phase EuIIEuIII2Ta2N4O3

“…Some Eu‐containing nitride oxide perovskites, such as Ca 1– x EuTa(N,O) 3 , EuWN 2– x O 1+ x (x = –0.16 – 0.46), EuWN 1.42 O 1.58 and Eu M NO 2 ( M = Nb, Ta) can be synthesized by ammonolysis of oxide precursors, obtained by ceramic or citrate routes in flowing gaseous NH 3 at elevated temperatures between 870 – 1173 K. At other temperatures, either decomposition of respective nitride oxides or no formation of these compounds was observed. For example, the formation of scheelite‐type phases can be suppressed by thermal treatment . Therefore, different temperatures, precursors and intermediate grinding steps have been necessary for successful synthesis of nitride oxide perovskites …”

“…Accordingly, a number of oxides are known in this structure type and well examined . From oxides to nitride oxides, the anionic substitution of oxygen by nitrogen causes an increase in covalency of the metal‐ligand bonds, giving rise to a marked variation of the structural, optical and magnetic properties . In recent years, some nitrogen‐containing representatives of the Ruddlesden‐Popper phases, e.g.…”

“…[14,15] Combining Eu II with spin of S = 7/2 and transition metals like Nb, Ta and W results in interesting properties like low-temperature ferromagnetism [16] and colossal magnetoresistance [17] in nitride oxide perovskites. Some Eu-containing nitride oxide perovskites, such as Ca 1-x EuTa(N,O) 3 , [15] EuWN 2-x O 1+x (x = -0.16 -0.46), [18] EuWN 1.42 O 1.58 [19] and EuMNO 2 (M = Nb, Ta) [14][15][16] can be synthesized by ammonolysis of oxide precursors, obtained by ceramic or citrate routes in flowing gaseous NH 3 at elevated temperatures between 870 -1173 K. At other temperatures, either decomposition of respective nitride oxides or no formation of these compounds was observed. For example, the formation of scheelite-type phases can be suppressed by thermal treatment.…”