Neutron diffraction study of the inverse spinels Co2TiO4 and Co2SnO4

We report a detailed single crystal and powder neutron diffraction study of Co2TiO4 and Co2SnO4 between the temperature 1.6 and 80K to probe the spin structure in the ground state. For both compounds the strongest magnetic intensity was observed for the 111 M reflection due to ferrimagnetic ordering, which sets in below TN 48.6 and 41 K for Co2TiO4 and Co2SnO4, respectively. An additional low intensity magnetic reflection 200 M was noticed in Co2TiO4 due to the presence of an additional weak antiferromagnetic component. Interestingly, from both the powder and single crystal neutron data of Co2TiO4, we noticed a significant broadening of the magnetic 111 M reflection, which possibly results from the disordered character of the Ti and Co atoms on the B site. Practically, the same peak broadening was found for the neutron powder data of Co2SnO4. On the other hand, from our single crystal neutron diffraction data of Co2TiO4, we found a spontaneous increase of particular nuclear Bragg reflections below the magnetic ordering temperature. Our data analysis showed that this unusual effect can be ascribed to the presence of anisotropic extinction, which is associated to a change of the mosaicity of the crystal. In this case, it can be expected that competing Jahn Teller effects acting along different crystallographic axes can induce anisotropic local strain. In fact, for both ions Ti3 and Co3 , the 2tg levels split into a lower dxy level yielding a higher twofold degenerate dxz dyz level. As a consequence, one can expect a tetragonal distortion in Co2TiO4 with c a lt; 1, which we could not significantly detect in the present wor

Combining Sentinel-1 and Sentinel-2 data for improved land use and land cover mapping of monsoon regions

Land use and land cover maps can support our understanding of coupled human-environment systems and provide important information for environmental modeling and water resource management. Satellite data are a valuable source for land use and land cover mapping. However, cloud-free or weather independent data are necessary to map cloud-prone regions. This particularly applies to monsoon regions such as the Chennai basin, located in the north of Tamil Nadu and the south of Andhra Pradesh, India, which is influenced by the South Asian Monsoon and has abundant cloud cover, throughout the monsoon season. The Basin is characterized by small-scale agriculture with multiple cropping seasons and the rapidly developing metropolitan area of Chennai. This study aims to generate a land use and land cover map of the Chennai Basin for the cropping season of Rabi 2015/16 and to assess the influence of combining the new ESA Copernicus satellites Sentinel-1 and -2 on classification accuracies. A Random Forest based wrapper approach was applied to select the most relevant radar (Sentinel-1) images for the combination with the optical (Sentinel-2) data. Area proportion weighted accuracy with 95% confidence interval were estimated for the Random Forest models, which differentiated 13 land cover classes. The highest overall accuracy of 91.53% ± 0.89 pp was achieved with a combination of 1 Sentinel-2 and 8 Sentinel-1 scenes. This is an improvement of 5.68 pp over a classification with Sentinel-2 data only. An addition of further Sentinel-1 scenes showed no improvement in overall accuracy. The strongest improvement in class-specific accuracy was achieved for paddy fields. This study shows for the first time how land use and land cover classifications in cloud-prone monsoon regions with small-scale agriculture and multiple cropping patterns can be improved by combining Sentinel-1 and Sentinel-2 data

Atomic structure and magnetic properties of Fe–Nb–B metallic glasses

The short-range atomic order of ternary Fe–Nb–B metallic glasses has been studied by X-ray diffraction, neutron diffraction, X-ray absorption spectroscopy, and reverse Monte-Carlo simulation. The similarities and differences in the local structure of the Fe–Nb–B glasses and their crystalline counterparts are revealed. The composition dependences for the Curie temperature of the Fe–Nb–B glasses, which increases by substitution of boron for iron at constant niobium content and decreases by substitution of niobium for iron at constant boron concentration, are discussed in the frame of the coordination-bond model

A new type of La(Fe,Si)13-based magnetocaloric composite with amorphous metallic matrix

We report on novel magnetocaloric composites based on La(Fe,Si)13 particles in an amorphous metallic matrix. Hot compaction at the glass transition temperature, Tg, of the matrix prevents crack formation as commonly occurs in conventional hot-compacted La(Fe,Si)13 material. This damage can affect the magnetocaloric performance. The approach in the present paper shows that the La(Fe,Si)13 particles stay intact due to the buffer-effect of the amorphous and ductile matrix at Tg. Therefore, the magnetocaloric properties of the composites are almost independent of the compaction pressures

Strong correlation between structure and magnetic ordering in tetragonally distorted off stoichiometric spinels Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4

We report a systematic study on the structural and magnetic properties of off stoichiometric polycrystalline bulk spinels Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4 using neutron and x ray diffraction, ferromagnetic resonance, and magnetic measurements. Both compounds show a weak tetragonal distortion with c a lt;1, where the crystal structure could be refined in the tetragonal space group I41 amd. Both Co2 and Cu2 ions are located at the tetrahedral A site, and Mn3 and Co3 at the octahedral B site. Ferrimagnetic FI ordering of Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4 sets in below 184 and 164 K, respectively. Magnetic structure analysis revealed that the ferrimagnetically coupled A2 and B3 site moments are aligned parallel to the tetragonal c axis. Additionally, a noncollinear antiferromagnetic order appears in the ab plane, where the moments point along [110] and [1 10]. The net magnetic moment [2 amp; 956;FI MnB CoB amp; 8722; amp; 956;FI CoA ] of Mn1.15Co1.85O4 obtained from neutron data varies between 0.88 1.08 amp; 956;B which is in good agreement with M 0.89 1.13 amp; 956;B as determined from magnetization measurements. However, for the Cu containing compound a larger discrepancy in the magnetic moment was observed between the neutron data 1.89 1.92 amp; 956;B and low temperature T 1.9 K field dependent H 90 kOe magnetization data 0.97 1.21 amp; 956;B . From the three sublattice model we obtained canting angles 28 amp; 8728; and 25 amp; 8728; for Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4, respectively. Both the bulk systems exhibit high magnetocrystalline anisotropy KU amp; 8764;9 105 and 7.5 105 erg cm3 and a field induced transition HD across 4.0 kOe due to the domain reorientation. Temperature 1.9 350 K and field 90 kOe dependence of magnetization data confirms the high spin S 32 and S 2 ground state configuration for both the divalent Co and trivalent M