O ct 2 00 1 Symmetry consideration and e g bands in NdNiO 3 and YNiO 3

Group theoretical analyses are applied to the magnetic and electronic structures of NdNiO3 and YNiO3, whose electronic structures have been studied very recently by the LSDA+U method. The space groups of the crystallographic structure of these materials are Pbnm and P21/n, respectively.[1,2] There are no Jahn-Teller distortion modes consistent with observed propagation vector of spin polarized neutrondiffraction. Two possible spin configurations (magnetic space groups) Camc21 and Pba are derived from Pbnm for NdNiO3. Then the electronic structures with each symmetry are studied by using the tight-binding model. Clear separation of partial density of states exists in Pba but does not in orthorhombic Camc21. The combination of results of the present work and the previous LSDA+U calculation shows that the ground state magnetic structure of NdNiO3 is monoclinic Pba. NdNiO3 has only one kind of Ni sites, while YNiO3 has two inequivalent Ni sites. The magnetic structure of YNiO3 is monoclinic Pb21/a, if one assumes no magnetic moment on Ni ions (Ni) on one of these inequivalent sites.