Colossal magnetoresistance accompanying a structural transition in a highly two-dimensional metallic state ofCa3Ru2O7

Abstract

We report the high-field magnetoresistivity, magnetization, and magnetostriction data of a bilayered ruthenate ${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ grown by a floating-zone method. The samples used in this study show metallic inplane conduction, but nonmetallic interplane conduction, below $30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$; these results are suggestive of a highly two-dimensional metallic ground state. We demonstrate here the existence of two types of field-induced metamagnetic transitions at 6 and $15\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, accompanied by the colossal magnetoresistance effect in the interplane conduction $[{\ensuremath{\rho}}_{c}(20\phantom{\rule{0.3em}{0ex}}\mathrm{T})∕{\ensuremath{\rho}}_{c}(0\phantom{\rule{0.3em}{0ex}}\mathrm{T})<{10}^{\ensuremath{-}3}]$. Interestingly, the higher-field transition is accompanied by large inplane lattice shrinkage that is sufficient to cause orbital polarization in nearly threefold ${t}_{2g}$ orbitals. The lattice change due to the magnetic field coincides with the discontinuity at $48\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ observed in the thermal contraction data, suggesting that the high-temperature crystal structure is restored by the application of a magnetic field. In this paper, we will discuss this anomalous coupling between spin, charge, and lattice in ${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ in terms of structural distortions.