Ferromagnetism and Large Negative Magnetoresistance in Pb Doped Bi–Sr–Co–O Misfit-Layer Compound

Abstract

Ferromagnetism and accompanying large negative magnetoresistance in Pb-substituted Bi-Sr-Co-O misfit-layer compound are investigated in detail. Recent structural analysis of (Bi,Pb)2Sr3Co2O9, which has been believed to be a Co analogue of Bi2Sr2CaCu2O 8+δ , revealed that it has a more complex structure including a CoO2 hexagonal layer [T. Yamamoto et al., Jpn. J. Appl. Phys. 39 (2000) L747]. Pb substitution for Bi not only introduces holes into the conducting CoO2 layers but also creates a certain amount of localized spins. Ferromagnetic transition appears at T = 3.2 K with small spontaneous magnetization along the c axis, and around the transition temperature large and anisotropic negative magnetoresistance was observed. This compound is the first example which shows ferromagnetic long-range order in a two-dimensional metallic hexagnonal CoO2 layer.

Out‐of‐plane transport in Bi2−xPbxSr2Co2Oy single crystals

“…Unlike it remaining non-metallic down to T c in most cuprates, the c-axis resistivity ρ c of Sr 2 RuO 4 is non-metallic (dρ c /dT < 0) above T M ≈ 130 K, and becomes metallic (dρ c /dT > 0) below T M , while the in-plane resistivity ρ ab is always metallic. This peculiar behavior has also been detected in layered metals such as NaCo 2 O 4 [2] and (Bi 1-x Pb x ) 2 M 2 Co 2 O y [3,4] (M = Ba or Sr), in which the layers appear as 'isolated' at high temperatures but connected at low temperatures to give a 3D system.…”

Impurity-induced transition and impurity-enhanced thermopower in the thermoelectric oxideNaCo2−xCuxTerasaki1, Tsukada2, Iguchi3 2002Phys. Rev. B883550View full textAdd to dashboardCite

“…This does not mean that NaCo 2 O 4 is far from the instability of phase transitions, but rather, is very susceptible to various transitions against various perturbations. In fact, Na 1.5 Co 2 O 4 exhibits a glassy behavior at 3 K due to structure instability of the γ phase [39], and (Bi,Pb)-Sr-Co-O shows a ferromagnetic transition at 4 K due to the lattice misfit [40].…”

Instabilities of interacting electrons on the triangular lattice

“…A one-band Hubbard model on the two-dimensional triangular lattice may be the simplest approach to describe the motion of the charge carriers in the layers. In the cobalt oxides there are signs of electronic correlations like weak ferromagnetism and high temperature Curie behavior of the susceptibility 5,6 . Therefore it is natural to ask whether the superconductivity in these materials arises due to electron-electron interactions.…”