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Atomic scale magnetism:  seeing spin state?


1“Atomic resolution imaging of nanometer sized spin-state superlattices in cobaltite films“. J. Gazquez, W. Luo, M. P. Oxley, M. Prange, M. A. Torija, M. Sharma, C. Leighton, S. T. Pantelides, S. J. Pennycok, M. Varela. Nanoletters 11, 973-976 (2011).

Text Box:
Real-space, atomic-resolution mapping of a spin state superlattice in La0.5Sr0.5CoO3-δ.

The first atomic-resolution mapping of cobalt spin states has been achieved by aberration-corrected scanning transmission electron microscopy. Being able to obtain this information on a local scale will resolve many of the mysteries of magnetic nanostructures, since the magnetic properties of materials are not solely determined by the local ordering of magnetic moments, but also their actual values (“spin states”). Like many atoms, Co can exhibit a low, intermediate or high spin state. Our work1 now maps the spin state of Co atoms in nanometer-sized pockets of cobaltite thin films. We see unexpected spin state superlattices associated with O vacancy ordering. Such ordering is not observed in the bulk and therefore cannot be studied by diffraction techniques that provide spatial averages. This demonstrates the need for this local technique. Atomic resolution electron energy loss spectroscopy in the aberration corrected scanning electron microscope thus becomes a uniquely powerful tool to unravel the mechanisms of magnetism and  spin state superlattices at the nanometer scale.

 Oak Ridge National Laboratory