International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators

4-8 May 2009, Vienna

Magnetism in Rare Earth Nickelates Studied by Muon Spin Rotation

F.J. Litterst¹, E.M. Baggio-Saitovitch², M.M. Abd-Elmeguid³, J.A. Alonso⁴, and H. Luetkens⁵

¹Technische Universität Braunschweig, Germany
²Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro, Brazil
³Universität Köln, Germany
⁴CSIC, Madrid, Spain
⁵Paul Scherrer Institut, Villigen, Switzerland

Corresponding Author: j.litterst@tu-bs.de

The metal to insulator transition at T_MI and related changes in structure and magnetic behavior in the rare-earth nickelates RNiO₃ have been intensively studied in recent years. Evidence for charge disproportiona-tion occurring at Ni in EuNiO₃, NdNiO₃ [1,2] and YNiO₃ [3] comes from Mössbauer spectroscopy using ⁵⁷Fe substituted for Ni as nuclear probe. For both EuNiO₃ and YNiO₃ T_MI is much higher than the Néel temperatures of T_N =210K and 150K, respectively. This is in contrast to the nickelates with larger R (like Nd) where T_MI , T_N and a structural transition are coinciding.

We have performed muon spin rotation (μSR) experiments at SμS PSI, Switzerland, both for
EuNiO₃ and YNiO₃ to trace the magnetic ordering and also the influence of doping. Whereas in other RNiO₃ the magnetic response is dominated by the moments of R, we have here the advantage of vanishing or nearly vanishing contributions from the Y and Eu moments allowing an undisturbed study of the Ni sublattice.

The EuNiO₃ susceptibility is untypical for an antiferromagnet. The moment is increasing below T_N and saturating only below about 120K. We relate this to induced moments caused by mixing with higher crystal electric field states to the J =0 ground state of Eu³⁺ . With μSR in zero magnetic field we observe muon spin rotation at several muon sites in completely magnetically ordered surrounding below T_N =210K. From the frequencies we conclude that the ratio of valence of the disproportionated Ni species cannot be more than about 50% in contrast to the Mössbauer data of the Fe doped samples. For YNiO₃ we find similar μSR results with T_N =150K, yet with significant differences due to the diamagnetism of Y. Notably both compounds reveal significant changes in magnetic response below T_N which will be discussed, as well as the discrepancies with the Mössbauer results.

[1] A. Caytuero et al., Phys. Rev. B 74 (2006) 094433.
[2] A. Caytuero et al., Phys. Rev. B 76 (2007) 193105.
[3] S.J. Kim et al., J. Am. Chem. Soc. 123 (2001) 8127.