Structural and magnetization density studies of La2NiO4.

摘要: Neutron diffraction experiments have been performed on single crystals of ${\mathrm{La}}_{2}$${\mathrm{NiO}}_{4}$. Above 70 K the structure is orthorhombic Bmab. At a first-order transition occurs to crystal that we believe be tetragonal P${4}_{2}$/ncm. With our resolution see no splitting peaks would indicate lower-symmetry Pccn. A crystallographic refinement 307 independent reflections from two different gives an R factor 6% for P${4}_{2}$/ncm phase. The also shows are stoichiometric with oxygen composition 4.02\ifmmode\pm\else\textpm\fi{}0.03. antiferromagnetic magnetic in which propagation and spin directions parallel [100], agreement other studies. ordered moment at T=10 (1.62\ifmmode\pm\else\textpm\fi{}0.05)${\ensuremath{\mu}}_{B}$ per Ni atom. According susceptibility measurements ${T}_{N}$\ensuremath{\simeq}650 ${\mathrm{La}}_{2}$${\mathrm{NiO}}_{4}$, but not checked this neutron experiment. No change 70-K transition, cannot exclude formation 2k temperature give rise same pattern In second part experiment induced form (H=4.6 T, applied [010] axis 5 K) has measured polarized neutrons. Our object was search covalency effects, particular evidence orbital ${p}_{x}$, ${p}_{y}$ orbitals oxygens Ni-O plane.We 18 three wavelengths. 7.9 m${\ensuremath{\mu}}_{B}$ molecule, good bulk measurements. Surprisingly, find any transfer or asphericity density planes. Instead new effects along long c axis. ${\mathrm{La}}^{3+}$ atoms develop positive suggest comes hybridization between La 5d O p bands.