Magnetic structures of the rare-earth chain nickelates R2R2BaNiO5 as studied by the optical spectroscopy of the Er probe

The rare-earth chain nickelates R2R2BaNiO5 (R=NdR=Nd, Sm, Eu, Gd, Dy, Ho, Er, and Tm) were studied by means of the spectroscopic Er probe. The magnetic ordering was registered and the splitting of the ground-state Kramers doublet of Er3+ as a function of temperature was measured for all the compounds studied. This information was used to analyze a possible orientation of ordered magnetic moments of the nickel ions. The magnetic structures found for R=HoR=Ho, Dy, Nd, Gd, Tm, and Er are in good agreement with literature data, those for R=SmR=Sm and Eu are predicted for the first time.

► Spectroscopic method was applied to study magnetic structure of R2R2BaNiO5 compounds.
► Splitting Δ of the ground state Kramers doublet of the Er3+ probe ion was measured.
► Δ is sensitive to the direction of internal magnetic field in the AFM-ordered state.
► The magnetic structures for R=SmR=Sm and Eu were determined for the first time.