Charge disproportionation in YNiO 3 : ESR and susceptibility study

CAUSA, M. T.; SÁNCHEZ, R. D.; TOVAR, M.; ALONSO, J. A.; MARTÍNEZ-LOPE, M. J.

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

APS

Lugar: NY; Año: 2003 vol. 68 p. 1 - 5

0163-1829

We present a study of the magnetic properties of YNiO3 in the paramagnetic range above and below the metal-insulator (MI) transition. The dc susceptibility χdc (measured up to 1000 K) is a decreasing function of T for T>150K (the Néel temperature) and we observe two different Curie-Weiss regimes corresponding to the metallic and insulating phases. In the metallic phase, this behavior seems to be associated with the small ionic radius of Y3+. An electron spin resonance (ESR) spectrum compatible with Ni2+ is visible in the insulating phase but only a fraction of the Ni ions contributes to this resonance. We explain the ESR and χdc behavior for T<TMI in terms of charge disproportionation of the type 2Ni3+→Ni2++Ni4+, associated with the previously observed structural transition across TMI. Effects of thermally excited electronic configurations on χdc are discussed.