Hybrid Quantum-Classical Monte-Carlo Study of a Molecule-Based Magnet

Using a Monte Carlo (MC) method, we study an effective model for the Fe(II)Fe(III) bimetallic oxalates. Within a hybrid quantum-classical MC algorithm, the Heisenberg S=2 and $S'=5/2$ spins on the Fe(II) and Fe(III) sites are updated using a quantum MC loop while the Ising-like orbital angular momenta on the Fe(II) sites are updated using a single-spin classical MC flip. The effective field acting on the orbital angular momenta depends on the quantum state of the system. We find that the mean-field phase diagram for the model is surprisingly robust with respect to fluctuations. In particular, the region displaying two compensation points shifts and shrinks but remains finite.Comment: 8 pages, 7 figure

Low-symmetry spin Hamiltonian and crystal field tensors analysis: Fe3+ in natrolite

Electron paramagnetic resonance study of a natural single crystal of natrolite was carried out at the frequency ν = 36.772 GHz at room temperature. The angular dependence of the four symmetry-related spectra of Fe3+in the three crystallographic planes was fitted to a spin Hamiltonian (S = 5/2) of symmetry Ci. The rank 4 crystal field tensors at tetrahedral sites were calculated using the point-charge model to determine the principal axes orientations of their cubic and trigonal components. The analysis of zero-field splitting tensors and comparison with crystal field ones suggests that Fe3+ substitutes for Al3+ with no significant distortion of the coordination tetrahedron in natrolite. Comparison of data for several natural and synthetic crystals reveals that the 4-rank zero-field splitting tensor invariants for Fe3+ at the tetrahedral oxygen-coordinated sites are distinguishably smaller than those for Fe3+ at octahedral sites. Such comparative analysis may help to determine the substitutional sites in other crystals. © 2002 Elsevier Science (USA)

Multifrequency EPR study of Cr3+ ions in LiScGeO4

An electron paramagnetic resonance study of a synthetic single crystal of Cr-doped LiScGeO4 was carried out at the X-and Q-bands at 300 K and at the broad band (70-370 GHz) at 4.2 K. It was established that the EPR spectra with the magnetic multiplicity KM = 2 observed in all the frequency bands are due to the Cr3+ substituted for Sc3+ at the mirror symmetry octahedral site. The angular dependences of the two symmetry-related spectra of Cr3+ in the three crystallographic planes were fitted with the spin Hamiltonian (S = 3/2) of monoclinic symmetry. The zero-field splitting of the ground state energy levels was determined as 1.309(5) cm-1 which compares well with that for Cr3+ in forsterite and alexandrite crystals with similar olivine-like structure. Additional weak lines due to Mn2+ and Fe3+ at the mirror symmetry sites were also identified in the X- and Q-band spectra

Molecular and electronic structure of terminal and alkali metal-capped uranium(V) nitride complexes

Determining the electronic structure of actinide complexes is intrinsically challenging because inter-electronic repulsion, crystal field, and spin–orbit coupling effects can be of similar magnitude. Moreover, such efforts have been hampered by the lack of structurally analogous families of complexes to study. Here we report an improved method to U≡N triple bonds, and assemble a family of uranium(V) nitrides. Along with an isoelectronic oxo, we quantify the electronic structure of this 5f1 family by magnetometry, optical and electron paramagnetic resonance (EPR) spectroscopies and modelling. Thus, we define the relative importance of the spin–orbit and crystal field interactions, and explain the experimentally observed different ground states. We find optical absorption linewidths give a potential tool to identify spin–orbit coupled states, and show measurement of UV···UV super-exchange coupling in dimers by EPR. We show that observed slow magnetic relaxation occurs via two-phonon processes, with no obvious correlation to the crystal field

Этимологический анализ специальных единиц лексико-семантического поля "интеллектуальные энергетические системы" в системе современного английского языка

В данной статье описываются результаты этимологического анализа лексико-семантического поля "Интеллектуальные энергетические системы" современного английского языка. Этимологический анализ проводится в аспекте "семантической эволюции слова", а также принадлежности слова к собственному или заимствованному языковому материалу

Implications of Invalid Conversions between Crystal-Field Parameters and Zero-Field Splitting Ones Used in Superposition Model

The methodology used in recent study of the zero-field splitting parameters of $Cr^{3+}$ ions at various orthorhombic symmetry sites in $LiKSO_4$ by Pandey and Kripal is critically commented on. We argue that the crystal field parameters, $B_{kq}$, in the Wybourne notation, which were calculated using the superposition model for $Cr^{3+}$ ions in $LiKSO_4$, may only be converted into the crystal field parameters in the Stevens notation. Regrettably, the authors have also converted the latter parameters supposedly into the zero-field splitting parameters D and E in the conventional notation. Such direct conversions are fundamentally incorrect and constitute factual invalid usage of the conversion relations between the crystal field (ligand field) parameters and the zero-field splitting ones. The cases of an implied usage of the invalid conversion relations between the crystal field parameters and the zero-field splitting parameters occurring in recent literature are also outlined. Pandey and Kripal have found the zero-field splitting parameters theoretically evaluated in this way to be in good agreement with the experimental values. However, the faulty methodology renders the conclusion that $Cr^{3+}$ ions enter into the $LiKSO_4$ lattice at the substitutional $K^{+}$ sites unjustified. Several other conceptual problems arising from misinterpretations of the crucial notions identified therein are also discussed and clarified