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Competition between ferromagnetism and spin glass: The key for large magnetoresistance in oxygen-deficient perovskites Sr Co 1 − x M x O <mml:…

2005; American Physical Society; Volume: 71; Issue: 21 Linguagem: Inglês

10.1103/physrevb.71.214424

1550-235X

Teruki Motohashi, V. Caignaert, V. Pralong, M. Hervieu, A. Maignan, B. Raveau,

Multiferroics and related materials

The magnetic and magnetotransport properties of the oxygen deficient perovskites, $\mathrm{Sr}{\mathrm{Co}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ with $M=\mathrm{Nb}$ and Ru, were investigated. Both Nb- and Ru-substituted cobaltites are weak ferromagnets, with transition temperatures ${T}_{m}$ of $130--150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $130--180\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, respectively, and both exhibit a spin glass behavior at temperatures below ${T}_{f}=80--90\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. It is demonstrated that there exists a strong competition between ferromagnetism and spin glass state, where ${\mathrm{Co}}^{4+}$ induces ferromagnetism, whereas Nb or Ru substitution at the cobalt sites induces magnetic disorder, and this particular magnetic behavior is the origin of large negative magnetoresistance of these oxides, reaching up to 30% at $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in $7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. The differences between Nb- and Ru-substituted cobaltites are discussed on the basis of the different electronic configuration of niobium and ruthenium cations.