Large magnetoresistance in a ferromagnetic cobaltite: The 12H Ba0.9CoO2.6

The magnetic and transport properties of a hexagonal cobaltite related to the perovskite structure have been studied. By combining transmission electron microscopy, X-ray powder diffraction and iodometric titration, it is found that Ba0.9CoO2.6 crystallizes in the 12H structure [P63/mmc, a=5.6612 (1) Å and c=28.4627(8) Å]. Interestingly, this compound is a ferromagnet with a Curie temperature TC=50 K and a saturation magnetization MS2.5K=1.2μB/Co. This value is smaller than expected from the effective paramagnetic moment, μeff=3.7μB/Co, corresponding to an average spin S∼32 per Co, from which one would expect MSexp.=3μB/Co. This suggests either a canted structure or a strong local magnetic anisotropy related to the crystal field of the CoOn polyhedra. A clear transition in the electrical resistivity is found at TC consistent with a spin scattering reduction as the sample becomes ferromagnetic. The spin–charge coupling is evidenced by the large negative magnetoresistance effect optimum near TC=50 K, with [100×(ρH=7T-ρH=0T)/ρH=0T]=-60%.

Isothermal magnetic field-dependent magnetoresistance of the 12HBa0.9 CoO2.6. A negative value of −60% is reached in 7T at TC=50K.Figure optionsDownload as PowerPoint slide