Electron-spin-resonance in the doped spin-Peierls compound Cu(1-x)Ni(x)GeO3

ESR-study of the Ni-doped spin-Peierls compound CuGeO3 has been performed in the frequency range 9-75 GHz. At low temperatures the g-factor is smaller than the value expected for Cu- and Ni-ions. This anomaly is explained by the formation of magnetic clusters around the Ni-ions within a nonmagnetic spin-Peierls matrix. The transition into the AFM-state detected earlier by neutron scattering for doped samples was studied by means of ESR. For x=0.032 a gap in the magnetic resonance spectrum is found below the Neel temperature and the spectrum is well described by the theory of antiferromagnetic resonance based on the molecular field approximation. For x=0.017 the spectrum below the Neel point remained gapless. The gapless spectrum of the antiferromagnetic state in weekly doped samples is attributed to the small value of the Neel order parameter and to the magnetically disordered spin-Peierls background.Comment: 16 pages, LATEX, 12 figures, submitted to Journal of Physics : Condensed Matte

Magnetic Resonance of the Intrinsic Defects of the Spin-Peierls Magnet CuGeO3

ESR of the pure monocrystals of CuGeO3 is studied in the frequency range 9-75 GHz and in the temperature interval 1.2-25 K. The splitting of the ESR line into several spectral components is observed below 5 K, in the temperature range where the magnetic susceptibility is suppressed by the spin-Peierls dimerization. The analysis of the magnetic resonance signals allows one to separate the signals of the S=1/2- and S=1 defects of the spin-Peierls phase. The value of g-factor of these signals is close to that of the Cu-ion. The additional line of the magnetic resonance is characterized by an anomalous value of the g-factor and by the threshold-like increase of the microwave susceptibility when the microwave power is increasing. The ESR signals are supposingly attributed to two types of the planar magnetic defects, arising at the boundaries of the domains of the spin-Peierls state with the different values of the phase of the dimerization.Comment: LATEX-text, 12 PS-figures, typos corrected, LATEX-style change

Summer Time Distribution of Sedentary and Migratory Individuals of the Baikal Grayling Thymallus baicalensis in the Tributaries of the Thermally Altered Section of the Yenisei River

Изменение температурного режима Енисея в нижнем бьефе ГЭС создало условия, позволяющие местной популяции байкальского хариуса осуществлять все стадии жизненного цикла в основном русле реки, без необходимости миграции в притоки, роль которых в поддержании популяционной структуры вида остается неизвестной. Целью проведенных в июле-августе 2021 года исследований стала оценка присутствия особей хариуса в пяти различных по протяженности притоках Енисея в районе г. Красноярска, а также их дифференциация по происхождению на основании анализа структуры чешуи и темпов роста. Полученные результаты свидетельствуют о неоднородном пространственном распределении вида в исследованных притоках, где он был представлен как оседлыми особями, так и мигрантами из основного русла Енисея. Область распространения хариуса в июле-августе была ограничена участками рек, температура воды в которых не превышала 16–17 ºС. Жилая медленнорастущая форма обнаружена в верхнем и среднем течении р. Березовка, а также на изолированных дамбами участках верхнего течения р. Кача. В крупных притоках Мана и Базаиха, на значительном удалении от их устья, отмечены мигранты из Енисея, с единичным присутствием оседлых особей. Таким образом, современная популяция байкальского хариуса на термически измененном участке реки Енисей включает рыб с разной миграционной активностью. Несмотря на меньшую биомассу зообентоса в притоках, по сравнению с основным руслом Енисея, преимуществом летней миграции в прогретые притоки может быть удлинение периода соматического роста рыб до 7 месяцевThe changes in the temperature regime of the Yenisei River downstream from the Krasnoyarsk Hydroelectric Power Plant have created conditions which allow the local population of the Baikal grayling to pass through all the stages of its life cycle in the main stream without migrating into the Yenisei tributaries, the role of the latter in maintaining the structure of the grayling population remaining unknown. The present research is aimed to determine the distribution of grayling in five Yenisei tributaries of different lengths in the vicinity of Krasnoyarsk and to investigate fish individuals’ origin based on comparative analysis of scale morphology and growth rate. The results indicate a heterogeneous spatial distribution of the species in the tributaries with both sedentary individuals and migrants from the mainstream of the Yenisei. Grayling distribution through July and August was limited to the river sections with water temperature up to 16–17 ºС. Slowly growing sedentary forms inhabit the upper and middle reaches of the Beryozovka River and the upper reaches of the Kacha River sections isolated by dams. Migrants from the Yenisei and single sedentary individuals were found at a considerable distance from the mouths of larger tributaries, the Mana and Bazaikha. Thus, the current population of the Baikal grayling in the thermally altered section of the Yenisei includes fish with different migration patterns. Although zoobenthos biomass is lower in the tributaries than in the mainstream of the Yenisei, a possible advantage of the summer migration into the warmed tributaries is the prolongation of the somatic growth period up to 7 month

Spin Transition Diagram of (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)2\text{}_{2}] Studied by EPR

The high-spin↔ low-spin transition in (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)$\text{}_{2}$] was studied by EPR under hydrostatic pressure in the temperature range of 80-310 K. Two modifications of the low-spin complexes: low-pressure (LS-1) and high-pressure (LS-2) ones were revealed. The low-spin complexes are associated in domains. Under atmospheric pressure LS-1 appears or disappears at 220 K. The hydrostatic pressure shifts the transition to high temperatures. Above 410 MPa the abrupt changes of the g-factor and width Δ B of the EPR line are observed. The pressure-induced transition LS-1 ↔ LS-2 is almost independent of T up to 275 K where under pressure 420 MPa a triple point is observed. When the pressure has been decreased the reverse transition from LS-2 to LS-1 or to high spin phase (at T>260 K) occurs with a large hysteresis about 95 MPa

EPR Discovery of a New Pressure-Induced Low-Spin Phase in (2Me-5Et-PyH)[Fe(Th-5Cl-Sa) 2

Electron paramagnetic resonance studies of the high-spin (HS) ↔ low-spin (LS) transition in 2-methyl-5-ethyl-pyridine-5-chloro-salicylalt hiosemicarbazonatoferrate(III) performed under hydrostatic pressure up to 500 MPa in a temperature range of 80-310 K have revealed two modifications of the low spin complexes: low-pressure (LS1) and high-pressure (LS2) ones. Under atmospheric pressure LS1 appears on cooling and disappears on heating at 220 K. The hydrostatic pressure shifts the transition to higher temperatures. Below 275 K an increase in pressure to 410 MPa results in abrupt changes in the g-factor and widthΔ B of the EPR line indicating a transition to a new phase. The pressure-induced transition LS1 ↔ LS2 is almost independent of T up to 275 K, where at a pressure of 420 MPa a triple point is observed. The LS1↔ LS2 and HS↔ LS2 (at T>260 K) transitions occur with a large hysteresis of about 95 MPa. The process of the spin transition has been shown to begin with the formation of domains of LS complexes in the matrix of HS ones. The response of the domains to external factors has been studied

Intramolecular and Lattice Dynamics in V6−nIV\text{}_{6-n}^{IV}VnV\text{}_{n}\text{}^{V} O7\text{}_{7}(OCH3\text{}_{3})12\text{}_{12} Crystal

Multi-nuclear mixed-valence clusters V$\text{}_{4}^{IV}$V$\text{}_{2}^{V}$O$\text{}_{7}$(OCH$\text{}_{3}$)$\text{}_{12}$ were studied by X-band EPR in the temperature range 4.2-300 K. An isotropic exchange interactions between four V$\text{}^{IV}$ ions with individual spin S$\text{}_{i}$=1/2 determine the energy levels structure of the compound with the total spin states S=0, 1, and 2, which are doubled and split due to the extra electron transfer. The spin-Hamiltonian approach was used for the analysis of the temperature dependences of the EPR spectra parameters and the cluster dynamics. Two types of the electron transfer are assumed: the single jump transfer leading to the splitting of the total spin states by intervals comparable in magnitude with the exchange parameter J≈100-150 cm$\text{}^{-1}$ and the double jump one resulting in dynamics. The dependence of the transition ratesν$\text{}_{tr}$ on the energy of the total spin states was observed. In particular, in the range 300-220 K theν$\text{}_{tr}$ ≈0.7×10$\text{}^{10}$ cm$\text{}^{-1}$ and below 180 K the ν$\text{}_{tr}$≈1×10$\text{}^{10}$ cm$\text{}^{-1}$ was estimated. The g-factors of the spin states were shown to depend on the values of the intermediate spins. A phase transition in the T-range 210-180 K leading to the change in the initial V$\text{}^{IV}$ ions localization was discovered

The Origin of EPR Signals in SrCuO2\text{}_{2} Ceramics

The origin and thermal evolution of the EPR signals in SrCuO$\text{}_{2}$ ceramics are studied. It has been shown that the EPR signals observed in this ceramic material are due to contamination with other phases. The axial signal is due to SrCu(OH)$\text{}_{4}$·H$\text{}_{2}$O, which is a product of water reactions with SrCuO$\text{}_{2}$