Muon-spin-relaxation study of magnetic order in RNiO3 (R=rare earth) below the metal-insulator transition.

Abstract

Resistivity and susceptibility measurements on the perovskite ${\mathrm{Nd}}_{0.7}$${\mathrm{La}}_{0.3}$${\mathrm{NiO}}_{3}$ reveal the coincidence of magnetic and metal-insulator transitions at ${\mathit{T}}_{\mathrm{MI}}$=110 K. Muon-spin-relaxation (\ensuremath{\mu}SR) has been used to characterize the magnetic order in the low-temperature insulating phase. Two magnetically inequivalent muon sites exist there below ${\mathit{T}}_{\mathrm{MI}}$. It is found that the crystallographically equivalent rare-earth planes split into two magnetically inequivalent planes below ${\mathit{T}}_{\mathrm{MI}}$, one plane containing ordered Nd ions, the other remaining paramagnetic down to low temperatures. This behavior is a consequence of the unusual magnetic order of the Ni ions below ${\mathit{T}}_{\mathrm{MI}}$, with the \ensuremath{\mu}SR data confirming the disappearance of the inversion center at the Ni site in the magnetic insulating regime of the R${\mathrm{NiO}}_{3}$ perovskites.