Temperature Evolution of Sodium Nitrite Structure in a Restricted Geometry

The NaNO$_{2}$ nanocomposite ferroelectric material in porous glass was studied by neutron diffraction. For the first time the details of the crystal structure including positions and anisotropic thermal parameters were determined for the solid material, embedded in a porous matrix, in ferro- and paraelectric phases. It is demonstrated that in the ferroelectric phase the structure is consistent with bulk data but above transition temperature the giant growth of amplitudes of thermal vibrations is observed, resulting in the formation of a "premelted state". Such a conclusion is in a good agreement with the results of dielectric measurements published earlier.Comment: 4 pages, 4 figure

Nanopillar spin filter tunnel junctions with manganite barriers.

The potential of a manganite ferromagnetic insulator in the field of spin-filtering has been demonstrated. For this, an ultrathin film of Sm0.75Sr0.25MnO3 is integrated as a barrier in an epitaxial oxide nanopillar tunnel junction and a high spin polarization of up to 75% at 5 K has been achieved. A large zero-bias anomaly observed in the dynamic conductance at low temperatures is explained in terms of the Kondo scattering model. In addition, a decrease in spin polarization at low bias and hysteretic magneto-resistance at low temperatures are reported. The results open up new possibilities for spin-electronics and suggest exploration of other manganites-based materials for the room temperature spin-filter applications.This work was partially supported by the ERC Advanced Integrators Grant “SUPERSPIN”. B.P. was funded by the Nehru Trust for Cambridge University and St John’s College. The TEM work at Texas A&M was supported by the U.S. National Science Foundation (NSF-DMR 0846504). The authors wish to thank Prof. J. Kumar (IIT Kanpur, India) for help in improving the manuscript.This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/nl500798

Structural and Magnetic Properties of Orthorhombic LixMnO₂

Rietveld refinement of the crystal and magnetic structures of LixMnO2 (x = 0.98, 1.00, 1.02) are performed using neutron and X-ray measurements. A significant structural disorder due to the presence of manganese ions in lithium positions (MnLi) and lithium ions in manganese ones (LiMn) is found to be a common feature of Li0.98MnO2, Li1.00MnO2, and Li1.02MnO2. An essential anisotropy of the thermal-expansion coefficients of the lithium manganese oxides is observed in the temperature range of 1.5-300 K. Furthermore, the distortion of the oxygen octahedral environment around the manganese ions decreases when the temperature lowers. This is attributed to the strong exchange interactions between parallel exchange-coupled Mn chains. First-principles calculations of the effective exchange-interaction parameters in Li16Mn16O32 confirm the essential antiferromagnetic interactions between the chains. In addition, a hypothetical (Li15Mn)Mn16O32 structure where a lithium atom located between the Mn double layers is replaced by a manganese atom is considered. The calculations reveal that the presence of such defects results in appearance of a ferromagnetic component that agrees with the magnetic measurements