Critical phenomena in 1D Ising model with arbitrary spin

The aim of this work was to study critical phenomena taking place in 1D Ising model with different exchange interactions signs and arbitrary spin values in a magnetic field. Exact analytical formulas for frustration fields, zero temperature magnetization and entropy at these fields are obtained. The general behavior of pair spin correlation function with the accounting of only interactions between nearest neighbors is examined. © 2018 The Authors, published by EDP Sciences.The reflorted study was carried out within the state assignment of FASO of Russia (theme «Quantum» n. 01201463332) and was funded by RFBR according to the research flroject n. 16-32-00032

Magnetic and magnetocaloric properties of (MnCo)1-xGe compounds

The crystal structure, magnetic properties, and heat capacity of the (MnCo)1-xGe compounds with x ≤ 0.05 have been studied. It was found that, as the deviation from the MnCoGe stoichiometric composition increases, the temperature of structural transition from the low-temperature phase with the orthorhombic TiNiSi-type structure to the high-temperature phase with the hexagonal Ni2In-type phase decreases rapidly, whereas the magnetic ordering temperature varies slightly. The temperature of structural transition for the composition with x = 0.02 approximately coincides with the Curie temperature of the hexagonal phase, and the transition is accompanied by a significant entropy change, namely, ΔS = 34 J/(kg K). The application of high magnetic field in the transition-temperature range causes an increase in the relative volume of the orthorhombic phase. An analysis of magnetocaloric properties of these compounds, which was performed with the formal application of the Maxwell's relationship near the temperature of first-order structural phase transition, is shown to give overestimated values of the entropy change. © Pleiades Publishing, Ltd., 2013

Irreversibility of the magnetic state of Tm1 xTbxCo2 revealed by specific heat, electrical resistivity, and neutron diffraction measurements

The substitution of Tb for Tm in the Laves phase compound Tm Co2 leads to appearance of a magnetic moment on the Co atoms through the metamagnetic transition in the itinerant d -electron subsystem and gives rise to long-range ferrimagnetic order in Tm1-x Tbx Co2 at x≥0.15. The magnetic state of the compound Tm0.9 Tb0.1 Co2, i.e., just below the critical Tb concentration, is characterized by the presence of large regions with short-range magnetic order and localized spin fluctuations (LSFs) induced in the Co 3d -electron subsystem by the fluctuating f-d exchange due to the Tm-Tb substitution. The peculiar magnetic state of this compound is strongly influenced by an external magnetic field which produces a first-order magnetic phase transition to a long-range ferrimagnetic state with the magnetic moment on the Co atoms up to (0.7-0.8) μB. This field-induced transition in Tm0.9 Tb0.1 Co2 is found to be irreversible. It is accompanied by a giant and irreversible reduction of the electrical resistivity (Δρ ρ∼-45%), specific heat (by about 3.7 times at 2 K), and intensity of magnetic neutron scattering. Such behavior is associated with the field-induced metamagnetic transition in the itinerant d -electron subsystem mediated by the f-d exchange. Significantly enhanced values of the residual resistivity and the coefficient γ of the T -linear contribution to the specific heat in the compound with x=0.1 as well as their unusual behavior with temperature and under application of the magnetic field is ascribed to the presence of LSF. © 2006 The American Physical Society.This work was partly performed at the Swiss Spallation Neutron Source SINQ, Paul Scherrer Institute (PSI), Villigen, Switzerland. This work was supported by the Russian Foundation for Basic Research (Grant No. 04-02-96060) and by the Swiss National Science Foundation (SCOPES Project No. IB7420-110849)

Identification of Populus nigra, P. laurifolia and P. × jrtyschensis by leaf petiole anatomy

Remarkable variability in morphology of the Populus genus, as well as widely spread hybridization within the genus complicate taxa identification. Petiole anatomy plays an important role in plant taxonomic attribution and resolution of arguments in systematics. The aim of the study was to examine the petiole anatomy of P. nigra, P. laurifolia and P. × jrtyschensis to assess its potential use for taxa identification. The leaf petioles were collected from 252 individual trees in 8 populations of P. nigra, P. laurifolia and P.× jrtyschensis in the area of their natural hybridization in the basin of the Tom River in Kemerovo Oblast. Two of those 8 populations, located far from the hybridization centers, were regarded as controls to characterize parent taxa. Cross sections were made in the upper part of petioles. Then the sections were used to examine the shape of petiole cross sections, the contour of the adaxial sides, the vascular system types and lower ring shape. The petioles of trees growing far from hybridization areas were found to differ in their vascular systems: P. nigra had a linear, while P. laurifolia a high­arc­shaped one. The hybrids were found to belong to several types of vascular systems, namely intermediate, high­intermediate, linear and high­arc­shaped ones. The intermediate type of vascular system is characteristic of the most part of P. × jrtyschensis trees (78 % of the total samplings). Therefore most of them can be classified as F1 hybrid and others – as a recombinant species. Examination of P. nigra in its natural hybridization center allowed finding an approach to the identification back­crosses. The study confirmed provides a solid basis for the identification of parent species, hybrids and backcrosses in natural hybridization areas of taxa belonging to Aigeiros and Tacamahaca sections of Populus genus

PHENETIC ANALYSIS OF POPULUS NIGRA, P. LAURIFOLIA AND P. × JRTYSCHENSIS IN NATURAL HYBRIDIZATION ZONE

The wide spread of hybridization in the genus Populus, including spontaneous hybridization, caused by cultivars, requires studying the variability and inheritance of morphological traits by hybrids for initial tracking of these processes. The analysis of endogenous, intra- and inter-population variability was performed on 533 individual poplar trees in seven populations of P. nigra, seven populations of P. laurifolia and four populations of P. × jrtyschensis in the Tom river basin. On each specimen, 15 leaves from short mid-crown branches were collected to determine the shape of the leaf blade, the shape of its tip and base, as well as the branch morphotype. Some biometric indicators were proposed for geometric assessment of the leaf blade shapes of poplar species. The analysis showed that of all the traits examined only the leaf blade shape did not meet the criterion for “phene”, since it is usually represented by several forms in the crown of one and the same tree. In all the species studied, the level of their intra-population diversity was found to be much higher than the inter-population one. According to the increase of intra-population variability of qualitative traits, the taxa could be ranked as P. nigra < P. laurifolia < P. × jrtyschensis. The share of inter-population diversity differed among the species studied, accounting for 21.5% in P. laurifolia, 13.8% in P. nigra and 8.0% in P. × jrtyschensis. The P. laurifolia populations showed the greatest inter-population differentiation, most likely because of a disjunct distribution due to narrow specialization to the montane river environment. The lower differentiation in P. nigra is probably due to the facts that this species dominates the poplar stands of the Tom River basin; its populations are not fragmented and are linked by vast gene flow. In P. nigra, an increase in the diversity of qualitative characteristics and phenotypes was observed in populations confined to hybridization centers. Natural selection is most likely the factor governing the inter-population differentiation in P. × jrtyschensis, leading to the predominance of F1 hybrids in populations and hence to a sharp decrease in inter-population variability

Ordering and frustrations in generalized Ising chain

The Ising model on a one-dimensional monoatomic equidistant lattice with different nearest-neighbour and second-neighbour exchange interactions is researched. Generalized Kramers-Wannier transfer-matrix with translation on two periods of a lattice is introduced. A property similar to supercooling and superheating is detected. At the triple points phases are not individualized, but completely frustrated which corresponds to the phenomenon of critical opalescence. Exact analytical expressions for free energy, heat capacity and entropy including zero-temperature entropy are obtained. Various new special cases were analyzed and compared with all known results. All frustration fields for magnetization, frustration values for the zero-temperature entropy and magnetization are found. © Published under licence by IOP Publishing Ltd.Ural Branch, Russian Academy of Sciences, UB RAS: 18-2-2-11The research was carried out within the state assignment of Minobrnauki of Russia (theme ”Quantum” No. AAAA-A18-118020190095-4), supported in part by Ural Branch of the Russian Academy of Sciences (project No. 18-2-2-11)