Interest to studies of gallium alloys increased recently in relation to their prospective applications for self-healing superconducting connections and wires. Special attention is focused on superconductive properties of nanostructured alloys. In the present work we studied the ac susceptibility of a porous glass/Ga-In-Sn nanocomposite within the temperature range from 1.9 to 8 K at bias fields up to 5 T. Two superconducting phase transitions were revealed with temperatures of 5.6 and 3.1 K. Phase diagrams were created. Positive curvature of the parts of critical lines was demonstrated and treated within the framework of a proximity effect model. Vortex activation barriers were found from shifts of the maxima of the imaginary parts of susceptibility with changing the ac frequency. A bend was shown on the field dependence of the activation barriers.

We present results of studies of superconductivity in a binary Bi-Sn alloy of the eutectic composition (57 wt.% Bi, 43 wt.% Sn). Temperature and field dependences of the dc magnetization were measured within a temperature range from 1.8 to 20 K in magnetic fields up to 20 kOe using a Quantum Design MPMS3 SQUID magnetometer. A two-stage phase transition with temperatures of the diamagnetism onset of 8.55 and 5.1 K was observed. A phase diagram was constructed. The coherence length for the first stage was estimated. The field dependence of the irreversibility temperature was found. Critical dependencies showed a positive curvature which was treated within the framework of the proximity effect model.

The results of studies of phase transitions of KNO3, embedded in carbon nanotubes, are presented. It is shown that for KNO3 particles in nanotubes, a narrowing of the tempera-ture range of the existence of the ferroelectric phase is observed, similarly to what hap-pens in ferroelectric semiconductors. The results obtained indicate that the external screening from the side of the conducting matrix acts similarly to the screening of spon-taneous polarization in conducting ferroelectrics.

Эвтектический сплав галлия и олова является перспективным материалом для использования в современной микроэлектронике, медицинской диагностике и гибкой робототехнике. В связи с новыми применениями сплава Ga-In, значительный интерес вызывают исследования влияния понижения размеров на свойства этого сплава. В настоящей работе приводятся результаты исследования методом ЯМР атомной подвижности в сегрегированной кристаллической фазе наноструктурированного сплава Ga-In, обогащенной галлием. Сплав с концентрацией 94 at.% Ga и 6 at.% In был введен в поры опаловой матрицы. Показано, что обогащенная галлием фаза имела структуру β-Ga. Проведены измерения температурной зависимости скорости ядерной спин-решеточной релаксации галлия. Разделены вклады магнитного дипольного и электрического квадрупольного механизмов релаксации. Рассчитано изменение с температурой времени корреляции атомного движения и оценена энергия активации. Ключевые слова: Ga-In сплав, наноконфайнмент в опале, сегрегированная фаза со структурой β-Ga, ЯМР, спин-решеточная релаксация галлия, атомная подвижность.

The discovery of extreme magnetoresistance (XMR) in non-magnetic materials attracted attention to the WTe2 semimetal. We have carried out studies of magnetoresistance in a tungsten ditelluride single crystal in the magnetic field range up to 14 T. Magnetoresistance increased with increasing field following a near quadratic law without saturation. The Shubnikov-de Haas oscillations were observed. Four fundamental frequencies were found in the oscillations spectrum, which correspond to two electron and two hole pockets caused by strong spin-orbit coupling.

The results of studying the linear and nonlinear dielectric properties of a new organic ferroelectric diisopropylammonium iodide (DIPAI), embedded in porous alumina films, in comparison with bulk DIPAI, are presented. It was found, for DIPAI in pores 300 and 60 nm in diameter the ferroelectric phase is formed in the heating and cooling modes in the temperature interval between two structural phase transitions above room temperature. No noticeable temperature hysteresis was observed for both phase transitions. It was shown that the boundaries of the intermediate polar phase for nanostructured DIPAI shift to low temperatures with decreasing pore size. For bulk DIPAI, two structural transitions were revealed during heating with the formation of an intermediate polar phase and only one transition during cooling, below which ferroelectricity occurred. The temperature of this transition was much lower than the corresponding temperature during heating. It is assumed that the observed differences in phase transitions for DIPAI in pores and bulk DIPAI are associated with acceleration of the phase transitions kinetics under conditions of nanoconfinement.

Исследованы особенности низкотемпературной теплоемкости, транспортные характеристики фононов в области гелиевых температур и наноструктурные неоднородности в монокристаллах твердых растворов эрбиевых моноалюминатов YAlO3 : Er, синтезированных методом направленной кристаллизации.

Changes in structure of a new molecular ferroelectric diisopropylammonium chloride (C6H16ClN, DIPAC) at room temperature were studied by high-resolution (CP-MAS) nuclear magnetic resonance (NMR) and X-ray analysis. NMR measurements were carried out for ^{13}С nuclei. Monoclinic ferroelectric and orthorhombic nonpolar phases as well as their coexistence were observed depending on time and thermal treatment. It was shown that the polar modification of DIPAC at room temperature transforms with time to the nonpolar orthorhombic structure. N. I. Uskova, E. V. Charnaya, L. Yu. Podorozhkin, S. V. Baryshnikov, I. V. Egorova, A. Yu. Milinskii

AbstractWe study the dc magnetization of a Bi_1.94Fe_0.06Se_3 single crystal in the temperature range of 1.9 to 400 K in applied magnetic fields up to 70 kOe for two sample orientations in the applied field. We register three magnetic phase transitions and observe considerable anisotropy of the magnetic properties. The coercive force varies with temperature in a nonmonotonic manner. For the sample in a paramagnetic state, we estimate its magnetic moment per iron atom; its Curie–Weiss temperature is found to be negative. Arrot–Belov plots are constructed.

We carried out 125Te NMR studies of a WTe2 topological Weyl semimetal at temperatures of 41 and 293 K. Measurements were performed using a pulse Bruker Avance 500 NMR spectrometer. 125Te NMR spectra were obtained for the WTe2 single crystal at the orientation of the crystalline c axis parallel and perpendicular to the quantized field. We ascribed the complex spectra to four non-equivalent tellurium sites in the WTe2 crystalline structure. The recovery of the longitudinal magnetization was studied after the pulse saturation of particular lines in the spectra. We observed the single-exponential relaxation. The frequency shifts and widths of the spectral lines differed insignificantly at two temperatures while the spin-lattice relaxation times at 41 K were by a factor of approximately 30 greater than the relevant times at room temperature. Strong temperature dependence of relaxation was suggested to be due to the contribution of Weyl quasi-particles below the topological phase transition.

AbstractIn this paper, we compared the results of a heat capacity study of an erbium-doped gallium gadolinium garnet crystal with data for an undoped garnet. The measurements were carried out in the temperature range from 1.9 to 220 K and in magnetic fields from 0 to 9 T. The temperature dependences of the specific heat were interpreted with allowance for the Schottky contributions due to the Gd^3+ and Er^3+ ions and the contributions of the thermal vibrations of the crystal lattice. The values of entropy and magnetic entropy are calculated.

AbstractThe temperature evolution of the Ga_94In_6 liquid alloy introduced into an opal matrix has been studied by the NMR method in the temperature range 300–155 K. The temperature dependences of the position and the intensity of the NMR signals from ^71Ga, ^69Ga, and ^115In isotopes have been measured upon cooling and heating of the nanocomposite. The ^71Ga NMR line has been observed to be split into two components on cooling below 176 K with a transfer of the intensity to the high-frequency component. The results demonstrate an induced by nanoconfinement shift of the eutectic point in the alloy and the liquid–liquid phase transition in the indium depleted part of the melt.

Проведены исследования температурной зависимости магнитной ac восприимчивости монокристаллического смешанного граната Er2HoAl5O12 в диапазоне от 1.8 до 300 K в нулевом постоянном поле и при приложении смещающих полей до 9 T. В отсутствие постоянного магнитного поля восприимчивость следовала закону Кюри-Вейсса. Приложение постоянного поля индуцировало магнитный фазовый переход, температура которого возрастала с ростом напряженности магнитного поля. Характерный для фазового перехода максимум динамической восприимчивости не демонстрировал заметной зависимости от частоты переменного поля. Работа выполнена при поддержке РФФИ (грант N 16-07-00181). Измерения проводились на оборудовании Ресурсного центра "Центр диагностики функциональных материалов для медицины, фармакологии и наноэлектроники", Научный парк СПбГУ. DOI: 10.21883/FTT.2017.04.44273.345