Interdependent scaling of long-range oxygen and magnetic ordering in nonstoichiometric Nd2NiO4.10

Abstract

Hole doping in Nd 2 NiO 4.00 can be achieved either by substituting the trivalent Nd atoms by bivalent alkalineearth metals or by oxygen doping, yielding Nd 2 NiO 4+δ . While the alkaline-earth-metal atoms are statistically distributed on the rare-earth sites, the extra oxygen atoms in the interstitial lattice remain mobile down to ambient temperature and allow complex ordering scenarios depending on δ and T . Thereby the oxygen ordering, usually setting in far above room temperature, adds an additional degree of freedom on top of charge, spin, and orbital ordering, which appear at much lower temperatures. In this study, we investigated the interplay between oxygen and spin ordering for a low oxygen doping concentration, i.e., Nd 2 NiO 4.10 . Although the extra oxygen doping level remains rather modest with only 1 out of 20 possible interstitial tetrahedral lattice sites occupied, we observed by single-crystal neutron diffraction the presence of a complex three-dimensional (3D) modulated structure related to oxygen ordering already at ambient, the modulation vectors being ±2/13a*±3/13b*, ±3/13b*±2/13b*, and ±1/5a*±1/2c*, and satellite reflections up to fourth order. Temperature-dependent neutron-diffraction studies indicate the coexistence of oxygen and magnetic ordering below T N 48 K, the wave vector of the Ni sublattice being k = (100). In addition, magnetic satellite reflections adapt exactly the same modulation vectors as found for the oxygen ordering, evidencing a unique coexistence of 3D modulated ordering for spin and oxygen ordering in Nd 2 NiO 4.10 . Temperature-dependent measurements of magnetic intensities suggest two magnetic phase transitions below 48 and 20 K, indicating two distinct onsets of magnetic ordering for the Ni and Nd sublattices, respectively.

Large-scale oxygen order phase transitions and fast ordering kinetics at moderate temperatures in Nd2NiO4+δ electrodes

“…These findings are fully equivalent to what is reported for the homologous Pr 2 NiO 4+ δ , indicating an oxygen diffusion pathway between apical and vacant interstitial sites in the [110]-direction inside the rock salt layer. Such a dynamical activation is also in agreement with a phonon-assisted diffusion mechanism, which becomes of importance in view of the diffusion pathway along [110], 7,13,15,19,42 showing a sequence of filled and empty (O ap ) 4 tetrahedra, of strongly different size (see Fig. 1c).…”

“…Below T N ≅ 50 K, antiferromagnetic ordering is observed, with magnetic modulation vectors identical to those observed for the oxygen ordering. 7 This clearly suggests that the magnetic ordering is directly influenced by the oxygen ordering. It underlines that strong correlations exist between structural and electronic ordering schemes, which condition in the case of Nd 2 NiO 4.10 the degree of freedom for electronic, i.e.…”

“…1–5 In this regard, non-stoichiometric 214-nickelates (Ln 2 NiO 4+ δ ; Ln = La, Pr or Nd) of the Ruddlesden–Popper (RP) series with layered K 2 NiF 4 structure appear as one of the most promising candidates due to their electronic complexity and enhanced oxygen mobility down to ambient temperature. 5–15 The crystal structure of these compounds, as shown in Fig. 1(a), can be described as a layered structure with alternate stacking of NiO 2 layers and rock salt type Ln 2 O 2 bilayers along the stacking-axis ( c -axis) of the tetragonal unit cell.…”

“…With increasing oxygen uptake the local distortions of the O int (O ap ) 4 tetrahedra get organized on a larger length scale, as evidenced by neutron and synchrotron diffraction experiments. 7,19,28–31 Ordering schemes of unprecedent structural complexity have been reported for the homologous Pr 2 NiO 4+ δ , where sub-mesoscopic ordering is observed for δ = 0.25 attaining translational periodicities of ca. 100 Å.…”

Evidence of correlated incommensurate structural and magnetic order in highly oxygen-doped layered nickelate Nd2NiO4.23

“…A relationship between the modulation vectors of the charge order and the interstitial order was reported for La 2 NiO 4.125 [6]. Moreover, a correlation between structural and magnetic orderings was recently evidenced for moderately oxygen-doped Nd 2 NiO 4.10 in which identical wave vectors were determined for the ordering of spins and excess oxygen atoms [20].…”