Electronic and magnetic properties ofLa2NiO4: The importance of La-O planes

Local spin-density calculations have revealed that the degree of the local distortion to the Ni-${\mathrm{O}}_6$ octahedra in ${\mathrm{La}}_2$ ${\mathrm{NiO}}_4$ has profound effects on its electronic and magnetic properties. In particular, the antiferromagnetism is strongly dependent on the ratio of the Ni-${\mathrm{O}}_{\mathrm{apex}}$ bond to Ni-${\mathrm{O}}_{\mathrm{planar}}$ bond length. When this bond-length ratio falls in between 1.00 and 1.08, the compound is a semiconducting antiferromagnet with an energy gap up to 0.5 eV. Orthorhombic lattice distortion, mainly obtained by rigidly tilting the Ni-${\mathrm{O}}_6$ octahedra, is found to strengthen the antiferromagnetism.