Magnetic ground state of pyrochlore oxides close to metal-insulator boundary probed by muon spin rotation

M. Miyazaki, R. Kadono, K. H. Satoh, M. Hiraishi, S. Takeshita, A. Koda, Ayako Yamamoto, H. Takagi

Research output: Contribution to journalArticle

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Abstract

The magnetism of ruthenium pyrochlore oxides A2Ru 2O7 (A=Hg, Cd, and Ca), whose electronic properties within a localized ion picture are characterized by nondegenerate t2g orbitals (Ru5+, 4 d3) and thereby subjected to geometrical frustration, has been investigated by the muon spin rotation/relaxation (μSR) technique. The A cation (mostly divalent) was varied to examine the effect of covalency (Hg>Cd>Ca) on the electronic property of the oxides. In a sample with A=Hg, which exhibits a clear metal-insulator (MI) transition below ∼100K (associated with a weak structural transition), a nearly commensurate magnetic order is observed to develop in accordance with MI transition. Meanwhile, in the case of A=Cd, where the MI transition is suppressed to the level of small anomaly in the resistivity, the local-field distribution probed by muons indicates emergence of a certain magnetic inhomogeneity below ∼30K. Moreover, in Ca2Ru2O7, which remains metallic, highly inhomogeneous local magnetism is found below ∼25K; this magnetism arises from randomly oriented Ru moments and thus is described as a "frozen spin-liquid" state. The systematic trend of increasing randomness and itinerant character with decreasing covalency suggests a close relationship between the two characters. To understand the effect of orbital degeneracy and associated Jahn-Teller instability, we examine a tetravalent ruthenium pyrochlore, Tl2Ru2O7 (Ru4+, 4 d 4). The result of μSR indicates a nonmagnetic ground state that is consistent with the formation of the Haldane chains suggested by the neutron-diffraction experiment.

Original languageEnglish
Article number094413
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume82
Issue number9
DOIs
Publication statusPublished - 2010 Sep 8
Externally publishedYes

Fingerprint

Metal insulator boundaries
muon spin rotation
Metal insulator transition
Magnetism
Oxides
Ground state
Ruthenium
insulators
Electronic properties
ground state
oxides
metals
ruthenium
Divalent Cations
Neutron diffraction
orbitals
frustration
Positive ions
electronics
Ions

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electronic, Optical and Magnetic Materials

Cite this

Magnetic ground state of pyrochlore oxides close to metal-insulator boundary probed by muon spin rotation. / Miyazaki, M.; Kadono, R.; Satoh, K. H.; Hiraishi, M.; Takeshita, S.; Koda, A.; Yamamoto, Ayako; Takagi, H.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 82, No. 9, 094413, 08.09.2010.

Research output: Contribution to journalArticle

Miyazaki, M. ; Kadono, R. ; Satoh, K. H. ; Hiraishi, M. ; Takeshita, S. ; Koda, A. ; Yamamoto, Ayako ; Takagi, H. / Magnetic ground state of pyrochlore oxides close to metal-insulator boundary probed by muon spin rotation. In: Physical Review B - Condensed Matter and Materials Physics. 2010 ; Vol. 82, No. 9.
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