We report on the main results of studying the electrical and magnetoresistance (MR) of a composite material consisting of 70 % mol. Dirac semi-metal Cd 3 As 2 and 30 % mol. ferromagnet MnAs at pressures up to 50 GPa in a diamond anvil cell with a «rounded cone-flat» type anvils, as well as magnetization at hydrostatic pressures up to 6 GPa in a toroid-shaped high-pressure cell, both at room temperature and in the temperature range of 180 – 350 K at atmospheric pressure. A mixture of methanol and ethanol in a ratio of 4:1 was used as a pressure transmitting medium. Elemental analysis of Cd 3 As 2 + 30 % mol MnAs composites showed that much of the volume is occupied by the Cd 3 As 2 phase. The proportion of MnAs phase inclusions is less than 5 %. The feature of Cd 3 As 2 + MnAs is the presence of a significant region of non-mixing of the Cd 3 As 2 and MnAs phase melts. A negative MR was revealed with increasing pressure in the entire studied baric zone. The maximum negative MR is observed in the baric zone of 22 – 26 GPa. Further increase in the pressure up to the maximum level result in the appearance of several extrema on the Δ R / R 0 ( P ) curve, with negative MR not exceeding 4 %. Upon pressure release from 50 GPa, the baric dependence of Δ R / R 0 ( P ) is characterized by an inversion of the MR sign: at pressures around 40 GPa, a negative MR is replaced by a positive MR, and at around 20 GPa, the maximum value of positive MR of ~5.3 % is observed. Signs of the instability of the monoclinic structure of Cd 3 As 2 resulted from its partial decomposition upon decompression were revealed. The results obtained can be used in spintronics when using appropriate composite materials.

Resistivity ρ, magnetoresistance Δρxx/ρ0(P) and Hall constant RH were measured in (Cd1 – xZnx)3As2 sample with х = 0.31 under the action of all-round pressure and at various temperatures in the range (80–400) K. These samples were obtained by the modified Bridgman method. The composition of the samples and their homogeneity were controlled by X-ray phase analysis and energy-dispersive X-ray spectroscopy. The results of energy dispersive X-ray spectroscopy showed that the distribution of elements in the sample is uniform. It was found that the resistivity increases with increasing temperature, and the change in ρ(T) has a metallic character. The Hall constant RH in the field decreases slightly with increasing temperature and retains a negative sign throughout the entire range under study. With increasing pressure, anomalies were observed in the baric dependences of the electrical resistivity ρ(Р), magnetoresistance Δρxx/ρ0(Р) and the Hall coefficient RH(Р). Increasing the confining pressure leads to suppression of the positive magnetoresistance. In the phase transition region, the negative magnetoresistance at a pressure Р (2.4–2.7) GPa in a field of 5 kOe is the maximum value of 1.7.

The resistivity ρ, magnetoresistance Δρ xx /ρ 0 ( P ), and Hall coefficient R H are measured in a (Cd 1 ‒ x Zn x ) 3 As 2 sample with х = 0.31 under the action of uniform pressure and at various temperatures in the range 80–400 K. These samples are obtained by the modified Bridgman method. The composition of the samples and their homogeneity are controlled by X-ray phase analysis and energy-dispersive X-ray spectroscopy. The results of energy dispersive X-ray spectroscopy show that the distribution of elements in the sample is uniform. It is found that the resistivity increases with increasing temperature, and the change in ρ( T ) has a metallic character. The Hall coefficient R H in the field decreases slightly with increasing temperature and retains a negative sign throughout the entire range under study. With increasing pressure, anomalies are observed in the baric dependences of the electrical resistivity ρ( Р ), magnetoresistance Δρ xx /ρ 0 ( Р ), and the Hall coefficient R H ( Р ). Increasing the uniform pressure leads to suppression of the positive magnetoresistance. In the phase-transition region, the negative magnetoresistance at a pressure of Р (2.4–2.7) GPa in a field of 5 kOe is a maximum value of 1.7.

The results of experimental studies of the resistivity, Hall effect, and magnetoresistance of Cd3As2 + kMnAs composites (k = 20, 30, 44.7 mol

In this article, we report research data for the isothermal magnetization of a composite consisting of Cd3As2 Dirac semimetal and MnAs ferromagnet (30 mol %) at pressures up to 5 GPa. A magnetic transformation in MnAs inclusions, the size of which presumably varies from a micro- to nanoscale, has been found to be similar to that in bulk MnAs compound, except for a hysteresis in the range of magnetostructural transformation. Under hydrostatic pressure, a magnetization maximum has been revealed at pressures P ≥ 0.77 GPa, which is indicative of ferromagnetic ordering improvement. The conclusion has been drawn that that the above features are due to the superparamagnetic nature of nanometer-sized MnAs inclusions in the Cd3As2 matrix.

The results of studying the thermal emf of composites Cd3As2 + n mol % MnAs (n = 10, 20, 30, 44.7) at high pressures up to 50 GPa are presented. In the pressure ranges of P = 28–35 GPa (n = 10, 20), 20–35 GPa (n = 30), and 30–35 GPa (n = 44.7), all the materials studied exhibit specific features in the behavior of the thermal emf S(P) (extrema, inflection points on the curves or hysteresis). At a pressure exceeding 40 GPa, the thermal emf changes weakly or barely changes with an increase and a subsequent decrease in pressure.

For the first time, the temperature dependences of the electrical resistivity and magnetization of the Cd48.6Mn11.4As40 nanocomposite were measured in the temperature range of 10–350 K. It is shown that the electrical properties of Cd48.6Mn11.4As40 are associated with spin polarization of intrinsic electrons in the Cd3As2 matrix by spin-polarized electrons injected into it from ferromagnetic MnAs nanoclusters. With an increase in the magnetization of the entire sample, the angle between the magnetization directions of individual nanoclusters decreases and the spin-polarized current increases. Furthermore, an increase in the concentration of intrinsic carriers in the matrix leads to an increase in the spin-polarized current. This concept is also confirmed by measurements of current–voltage characteristics (CVCs) at voltages of up to 5 V at temperatures both below critical temperature Tcg = 241 K of cluster glass formation (at 77 and 172 K) and above it (at 273.15 and 373.15 K), which exhibit an increasing deviation from the ohmic behavior with an increase in the stress. This means that the greater the spin polarization of intrinsic electrons in Cd3As2 due to an increase in the injection of spin-polarized electrons from MnAs with an increase in the voltage, the higher the current.

This work presents the results of studying the magnetization at pressures up to 5 GPa of a composite consisting of a Dirac semimetal Cd3As2 and 30 mol. % ferromagnet MnAs.

В нанокомзозите Cd48.6Mn11.4As40 в интервале температур 10-350 K впервые измерены температурные зависимости электросопротивления и намагниченности. Показано, что электрофизические свойства Cd48.6Mn11.4As40 обусловлены спиновой поляризацией собственных электронов в матрице Cd3As2 спин-поляризованными электронами, инжектируемыми в нее из ферромагнитных нанокластеров MnAs. С ростом намагниченности всего образца, угол между намагниченностями отдельных нанокластеров уменьшается и спин-поляризованный ток возрастает. Кроме того, повышение концентрации собственных носителей в матрице приводит к увеличению спин-поляризованного тока. Эта концепция подтверждается и измерениями вольтамперных характеристик (ВАХ) при напряжениях до 5 V при температурах как ниже критической температуры образования кластерного стекла Tcg=241 (при 77 и 172 K), так и выше нее (при 273.15 и 373.15 K), которые обнаруживают отклонение от омичности, возрастающее с напряжением. Это означает, что чем больше спиновая поляризация собственных электронов в Cd3As2, вследствие увеличения инжекции спин-поляризованных электронов из MnAs с напряжением, тем больше ток. Ключевые слова: спин, нанокомпозиты, вольт-амперные характеристики, сопротивление, спиновая поляризация, полупроводники, спиновая инжекция, намагниченность.

Представлены результаты исследования электро- и магнитосопротивления (МС) композита, состоящего из дираковского полуметалла Cd3As2 и 30 mol.% ферромагнетика MnAs при давлениях до 50 GPa. В диапазоне давлений 16-50 GPa наблюдалось гистерезисное поведение транспортных свойств при двух последовательных циклах приложения и снятия давления. Измерения МС в режиме подъема и сброса давления выявили особенности в виде максимумов отрицательного и положительного МС, величины относительного магнитосопротивления (Delta R/R0) достигали ~20 и ~5.3% соответственно. Установлена нестабильность моноклинной структуры Cd3As2 в результате ее частичного разложения при декомпрессии. Ключевые слова: высокое давление, композит, удельное электросопротивление, отрицательное магнитосопротивление, структурный фазовый переход.

Abstract The pressure dependences of electrical resistance, Hall coefficient, charge carrier mobilities, and magnetoresistance of the Cd_3As_2–20 mol % MnAs composite are investigated at pressures up to 9 GPa. The pressure dependences of all the listed properties exhibit features related to phase transitions. The presence of pressure-induced negative magnetoresistance is registered.

Samples of tricadmium diarsenide with MnAs nanogranules (44.7 mol % MnAs) are synthesized. The morphology of the samples is studied by X-ray phase analysis and electron microscopy. The electrical properties of tricadmium diarsenide with MnAs nanogranules are studied in a range of temperatures of 77–372 K. It is found that the voltammetric characteristics are symmetrical relative to the inversion of the voltage sign at this temperature, and their deviation from ohmicity at a certain threshold voltage and decrease in the region of ohmicity with the growth in temperature are determined by the increase in the breakdown probability in a field above 5 × 10 4 V/m.

The pressure dependences of electrical resistance, Hall coefficient, charge carrier mobilities, and magnetoresistance of the Cd 3 As 2 –20 mol % MnAs composite are investigated at pressures up to 9 GPa. The pressure dependences of all the listed properties exhibit features related to phase transitions. The presence of pressure-induced negative magnetoresistance is registered.

Синтезированы образцы диарсенида трикадмия с наногранулами MnAs (MnAs --- 44.7 mol.%). Структура образцов исследована методами рентгенофазного анализа и электронной микроскопии. Исследованы электрические свойства диарсенида трикадмия с наногранулами MnAs в интервале температур 77-372 K. Обнаружено, что вольт-амперные характеристики симметричны относительно инверсии знака напряжения при данной температуре, их отклонение от омичности при определенном пороговом значении напряжения и уменьшение участка омичности с ростом температуры обусловлены увеличением вероятности пробоя в поле выше 5·104 V/m. Ключевые слова: нанокомпозиты, вольт-амперные характеристики, сопротивление, отрицательный температурный коэффициент, тепловой пробой.

— We have studied the effect of hydrostatic pressure on the galvanomagnetic properties of a Cd 3 As 2 + 20 mol % MnAs alloy in a transverse magnetic field of up to 4 kOe. The pressure dependences of the Hall coefficient and resistivity for the alloy provide evidence of reversible phase transitions. The observed negative magnetoresistance of the alloy is shown to be induced by high pressure.