Search NASA⌕ Search

Engineering topics

Nelson-Cheeseman, B. B.

Publications and source records attributed to Nelson-Cheeseman, B. B..

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Interface ferromagnetism in a SrMnO 3 /LaMnO 3 superlattice

Resonant soft x-ray absorption measurements at the O K edge on a SrMnO 3 /LaMnO 3 superlattice show a shoulder at the energy of doped holes, which corresponds to the main peak of resonant scattering from the modulation in the doped hole density. Scattering line shape at the Mn L 3,2 edges has a strong variation below the ferromagnetic transition temperature. This variation has a period equal to half the superlattice superperiod and follows the development of the ferromagnetic moment, pointing to a ferromagnetic phase developing at the interfaces. It occurs at the resonant energies for Mn 3+ and Mn 4+ valences. A model for these observations is presented, which includes a double-exchange two-site orbital and the variation with temperature of the hopping frequency t ij between the two sites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Modified Magnetic Ground State in Nimn 2 O 4 Thin Films

The authors demonstrate the stabilization of a magnetic ground state in epitaxial NiMn 2 O 4 (NMO) thin films not observed in their bulk counterpart. Bulk NMO exhibits a magnetic transition from a paramagnetic phase to a collinear ferrimagnetic moment configuration below 110 K and to a canted moment configuration below 70 K. By contrast, as-grown NMO films exhibit a single magnetic transition at 60 K and annealed films exhibit the magnetic behavior found in bulk. Cation inversion and epitaxial strain are ruled out as possible causes for the new magnetic ground state in the as-grown films. However, a decrease in the octahedral Mn 4+ :Mn 3+ } concentration is observed and likely disrupts the double exchange that produces the magnetic state at intermediate temperatures. X-ray magnetic circular dichroism and bulk magnetometry indicate a canted ferrimagnetic state in all samples at low T. Together these results suggest that the collinear ferrimagnetic state observed in bulk NMO at intermediate temperatures is suppressed in the as grown NMO thin films due to a decrease in octahedral Mn 4+ , while the canted moment ferrimagnetic ordering is preserved below 60 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Diffraction from Oxide Superlattices - Stacking sequence Effects in Plan View

As nanoscience moves from observation to control, and electron microscope image interpretation becomes simplified by the new corrected TEMs, there is now a more realistic prospect than ever of both fabricating, with control at the atomic level, structures with wanted properties, and interpreting their bulk properties in terms of the atomic structures seen in the (S)TEM. For example, oxide superlattices may now be tailor-made by atomic-layer deposition to produce both conductive and ferromagnetic or antiferromagnetic interfaces by choice of stoichiometry and stacking sequence.

36 MATERIALS SCIENCE↗