Spin-resonance modes of the spin-gap magnet TlCuCl_3

Three kinds of magnetic resonance signals were detected in crystals of the spin-gap magnet TlCuCl_3. First, we have observed the microwave absorption due to the excitation of the transitions between the singlet ground state and the excited triplet states. This mode has the linear frequency-field dependence corresponding to the previously known value of the zero-field spin-gap of 156 GHz and to the closing of spin-gap at the magnetic field H_c of about 50 kOe. Second, the thermally activated resonance absorption due to the transitions between the spin sublevels of the triplet excitations was found. These sublevels are split by the crystal field and external magnetic field. Finally, we have observed antiferromagnetic resonance absorption in the field-induced antiferromagnetic phase above the critical field H_c. This resonance frequency is strongly anisotropic with respect to the direction of the magnetic field.Comment: v.2: typo correction (one of the field directions was misprinted in the v.1

ЭФФЕКТИВНОСТЬ И ПАТОГЕНЕТИЧЕСКАЯ НАПРАВЛЕННОСТЬ ФОТОФЕРЕЗА ПРИ АТИПИЧНОМ КРАСНОМ ПЛОСКОМ ЛИШАЕ

Lichen planus (LP) is an autoimmune disorder which is characterized by long lasting, recurrent course of a disease and by poor response to treatment (including systemic corticosteroids and cytostatics). Cutaneous and mucosal LP may present in atypical forms, several can transform to cancer with statistical confidence. Earlier, we have confirmed high clinical efficacy of photopheresis — method of adoptive immunotherapy in treatment of patients with typical LP.Target: research of clinical efficacy of photopheresis in complex trearment of atypical forms of cutaneous and mucosal LP.Materials and methods. There had been carried out a study of the clinical and immunological efficacy in two groups of patients: patients receiving complex therapy, which includes photopheresis with routine therapy (delagil, doxycycline and topical corticosteroids (I groupe — 23 patients) and receiving complex therapy, which includes photopheresis with single injection of methotrexate in dose of 10 mg with routine therapy ( II groupe — 18 patients).Results. In I group of patients immunological disorders were similar with results of earlier immunological studies in patients with lypical LP, among them increase in the number of CD16+-cells. In the II groupe immunological disorders were characterized by the rise of amount and activity of CD3+CD8+-lymphocytes. The high efficacy of Group I patient treatment was accompanied by the restoration of their tolerance to the skin antigenic structures, while maintaining the possibility for transendothelial migration of CD16 + cells. The effect of the treatment in Group II patients was also pronounced; however, due to the use of methotrexate, no normalization of the patients’ immune parameters was observed.Conclusion. The data obtained confirms the high clinical efficacy of photopheresis in both groups of patients and its pathogenic validity in patients suffering from atypical lichen ruber planus.Красный плоский лишай (КПЛ) — хроническое воспалительное заболевание кожи и слизистых оболочек. КПЛ рассматривается как аутоиммунный дерматоз, характеризующийся длительным, рецидивирующим течением, часто торпидный к проводимой терапии, в том числе системными кортикостеридами и цитостатиками. Выделяют атипичные формы КПЛ кожи и слизистых оболочек, некоторые из которых могут трансформироваться в рак со статистически значимой частотой. Ранее нами была доказана высокая эффективность метода адаптивной иммунотерапии — фотофереза (ФФ) в лечении больных типичным КПЛ.Цель: изучение клинической эффективности ФФ в комплексном лечении атипичного КПЛ кожи и слизистых.Материалы и методы. Проведено клинико-иммунологическое изучение эффективности ФФ в двух группах больных: получавших ФФ на фоне стандартной (делагилом, доксициклином и кортикостероидными мазями) терапии (I группа — 23 больных) и в комплексе с однократной внутримышечной инъекцией метотрексата в дозе 10 мг на фоне стандартной терапии (II группа — 18 больных).Результаты. В I группе больных характер иммунных нарушений был сходен с ранее полученными при типичном КПЛ, в том числе относительно повышения уровня CD16+-клеток. Во II группе иммунные нарушения характеризовались повышенным количеством и активностью CD3+CD8+-лимфоцитов. Высокая эффективность лечения больных I группы сопровождалась восстановлением толерантности к собственным антигенным структурам кожи при сохранении возможности для трансэндотелиальной миграции CD16+-клеток, во II группе лечение также было эффективно, но не сопровождалось нормализацией иммунных показателей ввиду применения метотрексата.Заключение. Полученные данные подтверждают высокую клиническую эффективность ФФ в обеих группах пациентов и его патогенетическую обоснованность при атипичном КПЛ кожи

Separation of the magnetic phases at the N\'{e}el point in the diluted spin-Peierls magnet CuGeO3

The impurity induced antiferromagnetic ordering of the doped spin-Peierls magnet Cu(1-x)Mg(x)GeO(3) was studied by ESR technique. Crystals with the Mg concentration x<4% demonstrate a coexistence of paramagnetic and antiferromagnetic ESR modes. This coexistence indicates the separation of a macroscopically uniform sample in the paramagnetic and antiferromagnetic phases. In the presence of the long-range spin-Peierls order (in a sample with x=1.71%) the volume of the antiferromagnetic phase immediately below the N\'{e}el point T_N is much smaller than the volume of the paramagnetic phase. In the presence of the short-range spin-Peierls order (in samples with x=2.88%, x= 3.2%) there are comparable volumes of paramagnetic and antiferromagnetic phases at T=T_N. The fraction of the antiferromagnetic phase increases with lowering temperature. In the absence of the spin-Peierls dimerization (at x=4.57%)the whole sample exhibits the transition into the antiferromagnetic state and there is no phase separation. The phase separation is explained by the consideration of clusters of staggered magnetization located near impurity atoms. In this model the areas occupied by coherently correlated spins expand with decreasing temperature and the percolation of the ordered area through a macroscopic distance occurs.Comment: 7pages, 10 figure

Investigation of thermal and magnetic properties of defects in a spin-gap compound NaV2O5

The specific heat, magnetic susceptibility and ESR signals of a Na-deficient vanadate Na_xV_2O_5 (x=1.00 - 0.90) were studied in the temperature range 0.07 - 10 K, well below the transition point to a spin-gap state. The contribution of defects provided by sodium vacancies to the specific heat was observed. It has a low temperature part which does not tend to zero till at least 0.3 K and a high temperature power-like tail appears above 2 K. Such dependence may correspond to the existence of local modes and correlations between defects in V-O layers. The magnetic measurements and ESR data reveal S=1/2 degrees of freedom for the defects, with their effective number increasing in temperature and under magnetic field. The latter results in the nonsaturating magnetization at low temperature. No long-range magnetic ordering in the system of defects was found. A model for the defects based on electron jumps near vacancies is proposed to explain the observed effects. The concept of a frustrated two-dimensional correlated magnet induced by the defects is considered to be responsible for the absence of magnetic ordering.Comment: 6 pages, 8 figure

Formation of the S = 1 paramagnetic centers in the bond-diluted spin-gap magnet (C4H12N2)(Cu2Cl6)

Recently found quasi-two dimensional metalloorganic compound (C4H12N2)(Cu2Cl6) (abbreviated PHCC) is an example of a spin-gap magnet. Its ground state is a nonmagnetic singlet separated from the triplet excitations by an energy gap of approximately 1 meV. This compound allows partial substitution of chlorine ions by bromine, which results in the modulation of the affected exchange bonds. We have found by means of electron spin resonance spectroscopy that this doping results in the formation of the gapless S = 1 paramagnetic centers. These centers can be interpreted as triplet excitations trapped in a potential well created by doping.ISSN:1742-6588ISSN:1742-659

Improving the design of horizontal continuous casting machines

15.00; Translated from Russian (Stal' 1986 (9) p. 31-32)SIGLEAvailable from British Library Document Supply Centre- DSC:9022.06(BISI--25538)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo