Antiferromagnetic Order in MnO Spherical Nanoparticles

We have performed unpolarized and polarized neutron diffraction experiments on monodisperse 8 nm and 13 nm antiferromagnetic MnO nanoparticles. For the 8 nm sample, the antiferromagnetic transition temperature $T_N$ (114 K) is suppressed compared to the bulk material (119 K) while for the 13 nm sample $T_N$ (120 K) is comparable to the bulk. The neutron diffraction data of the nanoparticles is well described using the bulk MnO magnetic structure but with a substantially reduced average magnetic moment of 4.2$\pm$0.3 $\mu_B$/Mn for the 8 nm sample and 3.9$\pm$0.2 $\mu_B$/Mn for the 13 nm sample. An analysis of the polarized neutron data on both samples shows that in an individual MnO nanoparticle about 80$$ of Mn ions order. These results can be explained by a structure in which the monodisperse nanoparticles studied here have a core that behaves similar to the bulk with a surface layer which does not contribute significantly to the magnetic order.Comment: 7 pages, 5 figure

Size matters: the value of small populations for wintering waterbirds

Protecting systematically selected areas of land is a major step towards biodiversity conservation worldwide. Indeed, the identification and designation of protected areas more often than not forms a core component of both national and international conservation policies. In this paper we provide an overview of those Special Protection Areas and Ramsar Sites that have been classified in Great Britain as of 1998/99 for a selection of wintering waterbird species, using bird count data from the Wetland Bird Survey. The performance of this network of sites is remarkable, particularly in comparison with published analyses of networks elsewhere in the world. Nevertheless, the current site-based approach, whilst having the great benefit of simplicity, is deliberately biased towards aggregating species at the expense of the more dispersed distribution species. To ensure that the network continues successfully to protect nationally and internationally important waterbird populations, efforts now need to concentrate on the derivation of species-specific representation targets and, in particular, the ways in which these can be incorporated into the site selection process. Although these analyses concern the performance of protected areas for waterbirds in Great Britain, the results have wide-ranging importance for conservation planning in general and the design of protected area networks

Third structure determination by powder diffractometry round robin (SDPDRR-3)

The results from a third structure determination by powder diffractometry (SDPD) round robin are discussed. From the 175 potential participants having downloaded the powder data, nine sent a total of 12 solutions (8 and 4 for samples 1 and 2, respectively, a tetrahydrated calcium tartrate and a lanthanum tungstate). Participants used seven different computer programs for structure solution (ESPOIR, EXPO, FOX, PSSP, SHELXS, SUPERFLIP, and TOPAS), applying Patterson, direct methods, direct space methods, and charge flipping approach. It is concluded that solving a structure from powder data remains a challenge, at least one order of magnitude more difficult than solving a problem with similar complexity from single-crystal data. Nevertheless, a few more steps in the direction of increasing the SDPD rate of success were accomplished since the two previous round robins: this time, not only the computer program developers were successful but also some users. No result was obtained from crystal structure prediction expert

Superconductivity in Co-doped SmFeAsO

Here we report the synthesis and basic characterization of SmFe1-xCoxAsO (x=0.10, 0.15). The parent compound SmFeAsO itself is not superconducting but shows an antiferromagnetic order near 150 K, which must be suppressed by doping before superconductivity emerges. With Co-doping in the FeAs planes, antiferromagnetic order is destroyed and superconductivity occurs at 15 K. Similar to LaFe1-xCoxAsO, the SmFe1-xCoxAsO system appears to tolerate considerable disorder in the FeAs planes. This result is important, which indicates difference between cuprare superconductors and the iron-based arsenide ones.Comment: 11 pages, 3 figure

How many bird and mammal extinctions has recent conservation action prevented?

Aichi Target 12 of the Convention on Biological Diversity (CBD) contains the aim to ‘prevent extinctions of known threatened species’. To measure the degree to which this was achieved, we used expert elicitation to estimate the number of bird and mammal species whose extinctions were prevented by conservation action in 1993–2020 (the lifetime of the CBD) and 2010–2020 (the timing of Aichi Target 12). We found that conservation action prevented 21–32 bird and 7–16 mammal extinctions since 1993, and 9–18 bird and two to seven mammal extinctions since 2010. Many remain highly threatened and may still become extinct. Considering that 10 bird and five mammal species did go extinct (or are strongly suspected to) since 1993, extinction rates would have been 2.9–4.2 times greater without conservation action. While policy commitments have fostered significant conservation achievements, future biodiversity action needs to be scaled up to avert additional extinctions

The non-centrosymmetric borate oxides, MBi2B2O7 (M=Ca, Sr)

Two novel noncentrosymmetric borates oxides, MBi2B2O7 or MBi2O(BO3)2 (MCa, Sr), have been synthesized by solid-state reactions in air at temperatures in the 600-700??C range. Their crystal structures have been determined ab initio and refined using powder neutron diffraction data. CaBi2B2O7 crystallizes in the orthorhombic Pna21 space group with a=8.9371(5)??, b=5.4771(3)??, c=12.5912(7)??, Z=4, Rwp=0.118, [chi]2=2.30. SrBi2B2O7 crystallizes in the hexagonal P63 space group with a=9.1404(4)??, c=13.0808(6)??, Z=6, Rwp=0.115, [chi]2=4.15. Large displacement parameters suggest the presence of disorder in SrBi2B2O7 as also revealed by diffuse 2?a superstructure reflections in electron diffraction patterns. Both structures are built of identical (001) neutral layers of corner-sharing BO3 triangles and MO6 trigonal prisms forming six-membered rings in which Bi2O groups are located. Adjacent layers are stacked in a staggered configuration and connected through weak Bi-O bonds. A moderate efficiency for second harmonic generation (SHG) has been measured for a powder sample of CaBi2B2O7 (deff=2deff(KDP)).NRC publication: Ye

The incommensurate magnetic structure of Er3Cu4Ge4 below 1 K

The magnetic structure of Er3Cu4Ge4 was previously studied down to 1.5 K by Wawrzynska et al. who found that the Er(2d) sublattice orders at 8 K in a commensurate, doubled structure (kd = [0 1/2 0]) with an Er moment close to the free-ion value of 9 \u3bcB. By contrast, the Er(4e) sublattice ordered at 3.5 K in an incommensurate structure (ke = [0 0.883(2) 0]) with a greatly reduced moment (about one-third of the free-ion value). We have extended this study by high-resolution neutron powder diffraction down to 0.34 K in an effort to establish if the Er(4e) sublattice eventually locks-in and attains its free-ion moment (in keeping with our 166Er M\uf6ssbauer work). We observed a change in the Er (4e) order, beginning at 1.4 K, leading to a magnetic structure at 0.34 K which has almost locked-in but with (ke = [0.1 2/3 0]) and a still-reduced Er moment.Peer reviewed: YesNRC publication: Ye

Low-background single-crystal silicon sample holders for neutron powder diffraction

Neutron diffraction measurements on weakly scattering or highly absorbing samples may demand custom mounting solutions. Two low-background sample holders based on inexpensive single-crystal silicon are described. One uses a conventional cylindrical geometry and is optimized for weakly scattering materials, while the other has a large-area flat-plate geometry and is designed for use with highly absorbing samples. Both holders yield much lower backgrounds than more conventional null-matrix or null-scattering materials and are essentially free from interfering Bragg peaks.NRC publication: Ye