27 research outputs found
Many-Spin Effects and Tunneling Properties of Magnetic Molecules
Spin tunneling in molecular magnets has attracted much attention, however
theoretical considerations of this phenomenon up to now have not taken into
account the many-spin nature of molecular magnets. We present, to our
knowledge, the first successful attempt of a realistic calculation of tunneling
splittings for Mn molecules, thus achieving a quantitatively accurate
many-spin description of a real molecular magnet in the energy interval ranging
from about 100 K down to 10 K. Comparison with the results of the
standard single-spin model shows that many-spin effects affect the tunneling
splittings considerably. The values of ground state splitting given by
single-spin and many-spin models differ from each other by a factor of five.Comment: 3REVTeX pages, 2 figure
Effect of ligand substitution on the exchange interactions in {Mn12}-type single-molecule magnets
We investigate how the ligand substitution affects the intra-molecular spin
exchange interactions, studying a prototypal family of single-molecule magnets
comprising dodecanuclear cluster molecules [Mn12O12(COOR)16]. We identify a
simple scheme based on accumulated Pauling electronegativity numbers (a.e.n.)
of the carboxylate ligand groups (R). The redistribution of the electron
density, controlled by a.e.n. of a ligand, changes the degree of hybridization
between 3d electrons of manganese and 2p electrons of oxygen atoms, thus
changing the exchange interactions. This scheme, despite its conceptual
simplicity, provides a strong correlation with the exchange energies associated
with carboxylate bridges, and is confirmed by the electronic structure
calculations taking into account the Coulomb correlations in magnetic
molecules.Comment: 18 pages, 1 table, 4 figures. Accepted to "Inorganic Chemistry
Exchange Interactions and High-Energy Spin States in Mn_12-acetate
We perform inelastic neutron scattering measurements on the molecular
nanomagnet Mn_12-acetate to measure the excitation spectrum up to 45meV (500K).
We isolate magnetic excitations in two groups at 5-6.5meV (60-75K) and
8-10.5meV (95-120K), with higher levels appearing only at 27meV (310K) and
31meV (360K). From a detailed characterization of the transition peaks we show
that all of the low-energy modes appear to be separate S = 9 excitations above
the S = 10 ground state, with the peak at 27meV (310K) corresponding to the
first S = 11 excitation. We consider a general model for the four exchange
interaction parameters of the molecule. The static susceptibility is computed
by high-temperature series expansion and the energy spectrum, matrix elements
and ground-state spin configuration by exact diagonalization. The theoretical
results are matched with experimental observation by inclusion of cluster
anisotropy parameters, revealing strong constraints on possible parameter sets.
We conclude that only a model with dominant exchange couplings J_1 ~ J_2 ~
5.5meV (65K) and small couplings J_3 ~ J_4 ~ 0.6meV (7K) is consistent with the
experimental data.Comment: 17 pages, 12 figure
Electronic structure of a Mn12 molecular magnet: Theory and experiment
金沢大学大学院自然科学研究科物質情報解析We used site-selective and element-specific resonant inelastic x-ray scattering (RIXS) to study the electronic structure and the electron interaction effects in the molecular magnet [Mn12 O12 (C H3 COO)16 (H2 O)4] 2C H3 COOH 4 H2 O, and compared the experimental data with the results of local spin density approximation +U electron structure calculations which include the on-site Coulomb interactions. We found a good agreement between theory and experiment for the Coulomb repulsion parameter U=4 eV. In particular, the p-d band separation of 1.8 eV has been found from the RIXS spectra, which is in accordance with the calculations. Similarly, the positions of the peaks in the XPS spectra agree with the calculated densities of p and d states. Using the results of the electronic structure calculations, we determined the intramolecular exchange parameters, and used them for diagonalization of the Mn12 spin Hamiltonian. The calculated exchanges gave the correct ground state with the total spin S=10. © 2007 The American Physical Society
The impact of different biochars on Stemphylium leaf blight SLB suppression and productivity of onion Allium cepa L.
Objectives: Onion is a highly consumed vegetable crop in many countries, being a vital component of every dish. Recent studies indicated that different plant residues’ and animal manure-based biochars have strong impacts on the growth and development of plants. However, the impact of these biochars on disease suppression remains elusive. Therefore, this two-year study assessed the impact of animal and plant residues-based biochars on the suppression of Stemphylium leaf blight (SLB) of onion and productivity of the crop. Methods: Three pyrolyzed biochars cotton sticks, wheat straw and poultry litter) were used in the study. Biochars were prepared in the laboratory and applied to soil prior to crop sowing in same concentration during both years of study. Results: Poultry litter biochar had the highest impact on allometric traits and productivity of onion, and successfully reduced SLB severity. The control treatment had the lowest productivity and the highest disease severity during both years of the study. The remaining biochars (cotton sticks and wheat straw) hadmoderate influence on growth and development of onion plants. The disease severity was higher compared to poultry litter; however, it was lower in both biochars than control treatment. It is concluded that different animal and plant residues-based biochars could be used to improve plant health. Nonetheless, the response of these biochars will be crop-specific. Conclusion: Poultry litter biochar can be successfully used to suppress SLB in onion and productivity of the crop. Nevertheless, the actual mechanisms involved in disease suppression warrant further investigation
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The history, development, and curriculum of the Institute of Musical Studies and the Higher Institute of Musical Art in Kuwait
The present study sought to provide a detailed and documented examination of the history, development, and curriculum of the Institute of Musical Studies (IMS) and the Higher Institute of Musical Arts (HIMA). The primary sources of the study were interviews of key individuals who helped to form the two schools and were involved in the education of the first students. Private and institutional archives were also utilized. Searches through the archives were conducted in order to document the official policies, rules, and regulations of the schools.This study is organized into five chapters. The first chapter is the introduction into the subject of music education in Kuwait. The second chapter examines the establishment of the Institute of Musical Studies and the Higher Institute of Musical Arts. The third chapter describes the rules and regulations established for the two schools, including the acceptance requirements, attendance, policies, graduation fulfillment, requirements, and the goals of the schools. The fourth chapter presents the curriculum that was established for all the students and any changes that have been made over the years. The fifth chapter includes summary, conclusions, and recommendations
Many-spin calculation of tunneling splittings in Mn12 magnetic molecules
We calculate the tunneling splittings in a Mn12 magnetic molecule taking into account its internal many-spin structure. We discuss the precision and reliability of these calculations and show that restricting the basis (limiting the number of excitations taken into account) may lead to significant error (orders of magnitude) in the resulting tunneling splittings for the lowest energy levels, so that an intuitive picture of different decoupled energy scales does not hold in this case.
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