Ferrimagnetism of the magnetoelectric compound Cu2_2OSeO3_3 probed by 77^{77}Se NMR

We present a thorough $^{77}$Se NMR study of a single crystal of the magnetoelectric compound Cu$_2$OSeO$_3$. The temperature dependence of the local electronic moments extracted from the NMR data is fully consistent with a magnetic phase transition from the high-T paramagnetic phase to a low-T ferrimagnetic state with 3/4 of the Cu$^{2+}$ ions aligned parallel and 1/4 aligned antiparallel to the applied field of 14.09 T. The transition to this 3up-1down magnetic state is not accompanied by any splitting of the NMR lines or any abrupt modification in their broadening, hence there is no observable reduction of the crystalline symmetry from its high-T cubic \textit{P}2$_1$3 space group. These results are in agreement with high resolution x-ray diffraction and magnetization data on powder samples reported previously by Bos {\it et al.} [Phys. Rev. B, {\bf 78}, 094416 (2008)]. We also develop a mean field theory description of the problem based on a microscopic spin Hamiltonian with one antiferromagnetic ($J_\text{afm}\simeq 68$ K) and one ferromagnetic ($J_\text{fm}\simeq -50$ K) nearest-neighbor exchange interaction

Orbital domain state and finite size scaling in ferromagnetic insulating manganites

55Mn and 139La NMR measurements on a high quality single crystal of ferromagnetic (FM) La0.80Ca20MnO3 demonstrate the formation of localized Mn(3+,4+) states below 70 K, accompanied with strong anomalous increase of certain FM neutron Bragg peaks. (55,139)(1/T1) spin-lattice relaxation rates diverge on approaching this temperature from below, signalling a genuine phase transition at T(tr) approx. 70 K. The increased local magnetic anisotropy of the low temperature phase, the cooling-rate dependence of the Bragg peaks, and the observed finite size scaling of T(tr) with Ca (hole) doping, are suggestive of freezing into an orbital domain state, precursor to a phase transition into an inhomogeneous orbitally ordered state embodying hole-rich walls.Comment: 4 pages, 4 figure

Domestication Trial of Synsepalum Stipulatum (Radlk.) Engl. in The Humid Tropical Climate of Kinshasa

The present study deals with the domestication trial of Synsepalum stipulatum (Radlk.) Engl. in the humid tropical climate of Kinshasa and aims at contributing to the domestication of the species. To achieve this, proceeded with two methodological approaches: observation and experimentation. The results obtained show that the effect of three seeds treatments: drying of the seeds on the sun, seeds unpulped in the bag kept under the shade for 14 days and no treatment on the germination of Synsepalum stipulatum seeds was evaluated on two types of substrates: potting soil and clay soil. The absence of seed treatment resulted in very high germination rates in potting soil (75 %) and significantly longer germination times (41 days in potting soil and 67 days in clay soil). Overall, germination was better (rate and emergence) in the potting soil (53.3 %) and poor in the clay soil (20 %). The monthly growth analysis in height is estimated at 16.2 ± 1.2 cm while that in diameter was estimated at 0.3 ± 0.0 cm. The fruit of the species contains elements riches in carbohydrates and very few lipids and proteins whose energy value was evaluated at 422.1 ± 0.6 calories per 100 grams of edible parts. Therefore, it is important to consider the promotion of the species in view of its nutritional value

The quantum origins of skyrmions and half-skyrmions in Cu2OSeO3

The Skyrme-particle, the $skyrmion$, was introduced over half a century ago and used to construct field theories for dense nuclear matter. But with skyrmions being mathematical objects - special types of topological solitons - they can emerge in much broader contexts. Recently skyrmions were observed in helimagnets, forming nanoscale spin-textures that hold promise as information carriers. Extending over length-scales much larger than the inter-atomic spacing, these skyrmions behave as large, classical objects, yet deep inside they are of quantum origin. Penetrating into their microscopic roots requires a multi-scale approach, spanning the full quantum to classical domain. By exploiting a natural separation of exchange energy scales, we achieve this for the first time in the skyrmionic Mott insulator Cu$_2$OSeO$_3$. Atomistic ab initio calculations reveal that its magnetic building blocks are strongly fluctuating Cu$_4$ tetrahedra. These spawn a continuum theory with a skyrmionic texture that agrees well with reported experiments. It also brings to light a decay of skyrmions into half-skyrmions in a specific temperature and magnetic field range. The theoretical multiscale approach explains the strong renormalization of the local moments and predicts further fingerprints of the quantum origin of magnetic skyrmions that can be observed in Cu$_2$OSeO$_3$, like weakly dispersive high-energy excitations associated with the Cu$_4$ tetrahedra, a weak antiferromagnetic modulation of the primary ferrimagnetic order, and a fractionalized skyrmion phase.Comment: 5 pages, 3 figure

Establishing the fundamental magnetic interactions in the chiral skyrmionic Mott insulator Cu2OSeO3 by terahertz electron spin resonance

The recent discovery of skyrmions in Cu$_2$OSeO$_3$ has established a new platform to create and manipulate skyrmionic spin textures. We use high-field electron spin resonance (ESR) spectroscopy combining a terahertz free electron laser and pulsed magnetic fields up to 64 T to probe and quantify its microscopic spin-spin interactions. Besides providing direct access to the long-wavelength Goldstone mode, this technique probes also the high-energy part of the excitation spectrum which is inaccessible by standard low-frequency ESR. Fitting the behavior of the observed modes in magnetic field to a theoretical framework establishes experimentally that the fundamental magnetic building blocks of this skyrmionic magnet are rigid, highly entangled and weakly coupled tetrahedra.Comment: 5 pages, 3 Figure

Ethnobotanical characterization of medicinal plants used in Kisantu and Mbanza-Ngungu territories, Kongo-Central Province in DR Congo (vol 17, 5, 2021)

Background: The phytotherapeutic knowledge of the Kongo people in the territories of Kisantu and Mbanza-Ngungu in Kongo-Central Province (DR Congo) is rapidly eroding. To document the remaining knowledge, we conducted an ethnobotanical survey on the most important medicinal plant species and diseases treated with them, as well as plants with therapeutic potential. We also checked for the cultural similarity in medicinal plant knowledge between the two territories and how knowledge about Kongo medicinal plants differs between different social groups. Methods: From June 2017 until February 2018 and from February 2019 until April 2019, we conducted a survey with 188 phytotherapists, selected using the snowball method and surveyed using semi-structured interviews. Voucher specimens were taken for identification. Ethnobotanical data were analyzed using medicinal use value (UVs), informant agreement ratio (IARs), informant consensus factor (ICF), and species therapeutic potential (STP). Rahman's similarity index was used for ethno-cultural comparison of medicinal plant knowledge between the two communities. Medicinal knowledge between different social groups was analyzed using non-parametric tests and Poisson regression. Results: A total of 231 plants (i.e., 227 botanical species, representing 192 genera and 79 families) were reportedly used to treat 103 diseases. Most abundant taxa were reported for the Fabaceae family (including 11.9% of species and 10.9% of genera). Most reported species (45.0%) were from anthropized areas. Leaves (39.4%), herbs (37.1%), decoction (41.7%), and oral ingestion (72%) were the most frequently cited plant part, botanical form, preparation, and administration method, respectively. Four of all inventoried species showed high UVS (> 0.05), whereas eight had an IAR of one. According to ICF, 31 diseases were mentioned. Highest ICF (>= 0.4) was observed for hemorrhoids (0.44), amoebiasis (0.43), and itchy rash (0.42). Fifty-four plant species were identified as likely possessing an interesting therapeutic potential. Low ethno-cultural similarity in medicinal knowledge (RSI = 16.6%) was found between the two territories. Analysis of the Kongo medicinal plant knowledge showed that the mean number of reported species and diseases vary considerably depending on gender, type, and residence of therapists (P < 0.05). Conclusion: Results prove that the Kongo phytopharmacopeia makes use of interesting medicinal plant species that could be further studied for conservation and pharmacological applications