Search

The Hall effect in single crystals of topological semimetals WTe2 and MoTe2 is studied in the temperature range from 2 to 100 K and in magnetic fields up to 9 T. It is established that the Hall resistivity of WTe2 shows a nonlinear dependence on the magnetic field at temperatures below 100 K. At the same time, the Hall resistivity of MoTe2 depends linearly on the magnetic field in the temperature range from 2 to 25 K and a nonlinear contribution appears at 50 K. Along with the known mechanism of compensation/decompensation of electron and hole charge carriers, the nonlinear dependence of the Hall resistivity of WTe2 and MoTe2 single crystals on the magnetic field is associated with the scattering of charge carriers on the surface. [ABSTRACT FROM AUTHOR]

The electrical resistivity, magnetic, and galvanomagnetic properties of the cast and rapid melt quenched Mn3Al Heusler alloy have been studied. Rapid melt quenching was found to result in changing the microstructure of the Mn3Al alloy, which leads to substantial changes in its electronic transport and magnetic properties. It was suggested that for the cast and rapid melt quenched Mn3Al alloy frustrated antiferromagnetic and almost compensated ferrimagnetic state could appear, respectively. It is shown that the preparation and treatment of the Mn3Al compound plays a substantial role in the formation of its electronic and magnetic characteristics. [ABSTRACT FROM AUTHOR]

Electrical resistivity, magnetoresistivity, and the Hall effect have been studied in a single crystal of topological semimetal WTe2 in the temperature range from 12 to 200 K under magnetic fields up to 9 T. A quadratic temperature dependence of the electrical resistivity in the absence of field and conductivity in a magnetic field is found at low temperatures, which appears to be associated with contributions from various scattering mechanisms. Single-band and two-band models were used to analyze data on the Hall effect and magnetoresistivity. These results indicate electron–hole compensation with a slight predominance of electron charge carriers. [ABSTRACT FROM AUTHOR]

Temperature dependences of electrical resistivity of Co2MnZ (Z = Al, Si, Ga, Ge, Sn) Heusler alloys were measured in a temperature range of 78–300 K; their magnetization was measured at 5 and 300 K in fields up to 30 kOe. It was found that, for the Co2MnAl and Co2MnGa alloys, the Mooij rule [Mooij J.H. Phys. Stat. Sol. (a). 1973. V. 17. P. 521] does not hold. A correlation between electronic and magnetic characteristics of the Co2MnZ alloys and atomic number of element Z is found. [ABSTRACT FROM AUTHOR]

WTe2 and MoTe2 single crystals were grown, some of them were quenched, and the following properties were studied: electroresistivity in the temperature range from 1.8 to 300 K, magnetoresistivity at temperatures from 1.8 to 300 K in magnetic fields of up to 9 T. On the one hand, quenching leads to dramatic changes in the behaviour and value of the electroresistivity of MoTe2; the type of the electroresistivity changes from "semiconductor" to "metallic", and the electroresistivity values of MoTe2 before and after quenching differ by 8 orders of magnitude (!) at low temperatures. On the other hand, quenching is shown not to lead to significant changes in the behaviour and value of the electroresistivity of WTe2. A relatively small increase in the electroresistivity of quenched WTe2 at low temperatures can be associated with the scattering of current carriers by structural defects. The magnetoresistivity of MoTe2 increases from 7 to 16% in a field of 9 T at a temperature of 12 K as a result of quenching. The magnetoresistivity of WTe2 is shown to reach ∼1700% in a field of 9 T at 2 K. The behaviour of the magnetoresistivity of non-quenched samples is typical for compensated conductors with a closed Fermi surface. [ABSTRACT FROM AUTHOR]

Parameters of the energy gap and, consequently, electronic, magnetic and galvanomagnetic properties in different X2YZ Heusler alloys can vary quite strongly. In particular, half-metallic ferromagnets (HMFs) and spin gapless semiconductors (SGSs) with almost 100% spin polarization of charge carriers are promising materials for spintronics. The changes in the electrical, magnetic and galvanomagnetic properties of the Co2YSi (Y = Ti, V, Cr, Mn, Fe) and Co2MnZ Heusler alloys (Z = Al, Si, Ga, Ge) in possible HMF- and/or SGS-states were followed and their interconnection was established. Significant changes in the values of the magnetization and residual resistivity were found. At the same time, the correlations between the changes in these electronic and magnetic characteristics depending on the number of valence electrons and spin polarization are observed. [ABSTRACT FROM AUTHOR]

The field dependence of magnetization at T = 4.2 K and in magnetic fields of up to 70 kOe, temperature dependences of magnetization (2 K < T < 300 K), heat capacity (2 K < T < 30 K) and magnetic susceptibility (2 K < T < 1000 K) for Mn1.99Co0.96Al1.05 and Mn1.79Co1.25Al0.96 alloys, closed in composition to the Mn2CoAl spin gapless semiconductor, were studied. Alloys studied were demonstrated to be the band ferromagnets. Their high-field (H > 11 kOe) magnetization is described in the Stoner models with the Rhodes-Wohlfarth parameter pRW = 1.3 for Mn1.99Co0.96Al1.05 and pRW = 2.3 for Mn1.79Co1.25Al0.96. When the composition deviates from the stoichiometric Mn2CoAl, the spontaneous moment decreases slightly, the effective moment, on the contrary, increases. In this case, a negative sign of the temperature-independent component of the paramagnetic susceptibility is observed. The density of states n(EF) at Fermi level and the Debye temperature ΘD of studied alloys have the usual values for 3d-metal alloys. [ABSTRACT FROM AUTHOR]

The electro- and magneto-transport as well as magnetic properties of Co2MeSi (Me = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys were studied. The electroresistivity was measured from 4.2 to 300 K, the galvanomagnetic properties (magnetoresistivity and Hall effect) were measured at T = 4.2 K in magnetic fields of up to 100 kOe, and the magnetization at T = 4.2 and 300 K in fields of up to 70 kOe. The normal and anomalous Hall coefficients, saturation magnetization, residual resistivity, current carrier concentration, coefficients at linear contributions into the electroresistivity and magnetoresistivity were obtained. It was shown that on the one hand, there is quite clear correlation between the electronic and magnetic characteristics of Heusler alloys studied, and the spin polarization coefficients of current carriers, taken from well know literature data, on the other hand. The obtained results can be used for creation of new materials for spintronics. [ABSTRACT FROM AUTHOR]

The residual resistivity, Hall effect, and magnetization of Co2YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys were considered at T = 4.2 K and in fields up to 100 kOe. It is shown that as the number of valence electrons z ranges from 26 to 32, significant changes in the residual resistivity ρ0, magnetization Ms, sign and magnitude of the normal R0 and anomalous RS Hall effect coefficients are observed during the transition from Co2TiSi to Co2NiSi. It is established that there is a clear correlation between the values ρ0, R0, RS and Ms, depending on the number z, which can be associated with the appearance of a half-metal ferromagnetic state and/or spin gapless semiconductor. As z changes, the anomalous Hall effect coefficient has a power-law dependence on the residual electrical resistivity with an exponent of k = 3.1, which diverges with existing theories but agrees well with the experimental data obtained earlier for similar half-metallic ferromagnetic Heusler alloys. [ABSTRACT FROM AUTHOR]

The electrical, magnetic, and galvanomagnetic properties of Mn2YAl Heusler alloys (Y = Ti, V, Cr, Mn, Fe, Co, Ni) were experimentally studied. The temperature dependences of the electrical resistivity were obtained in a wide temperature range of 4.2–1000 K. The field dependences of the magnetoresistivity and the Hall effect were measured at T = 4.2 K in magnetic fields of up to 100 kOe, and the magnetization in fields of up to 70 kOe. The systems under consideration demonstrate strong ferromagnetism or compensated ferrimagnetism and phase transitions with a change in the magnetic structure are possible. The variability of the electronic structure in the series of these alloys, including the states of a half-metallic ferromagnet and a spin gapless semiconductor, is discussed. [ABSTRACT FROM AUTHOR]

A topological semimetal PtSn4 single crystal is grown and the following properties are studied: its electrical resistivity in the temperature range from 4.2 to 300 K, galvanomagnetic properties at temperatures from 4.2 to 80 K and in magnetic fields of up to 100 kOe, and optical properties at room temperature. Theoretical calculations of the electronic structure are performed. It is shown that the residual resistivity is rather small: ρ0 = 0.47 μΩ cm, which is characteristic of a "good" metal. The ρ(T) dependence is of the metallic type, increasing monotonically with temperature. Analysis of the temperature dependences of the magnetoresistivity suggests that the Fermi surface of the PtSn4 compound may contain closed sheets. Studies of the Hall effect and the estimates made in the single-band model allowed us to conclude that the predominant type of current carriers are holes with concentration n = 6.8 × 1021 cm–3 and mobility μ ≈ 1950 cm2/(V s) at T = 4.2 K. It is shown that the optical properties of PtSn4 have features characteristic of "bad" metals. The calculation of the electronic structure of PtSn4 showed that, in general, this compound has a structure characteristic of metallic systems with a sufficiently large number of electronic states at the Fermi level, which is consistent with the experimental results on the electronic transport and optical properties of the PtSn4 single crystal. [ABSTRACT FROM AUTHOR]

Abstract: Studies of structural and phase transformations in the cast and melt-quenched ferromagnetic four-component alloy Ni54Mn20Fe1Ga25 were performed using transmission and scanning electron microscopy and X-ray diffraction, The obtained data have been compared with the results of studies of physical characteristics (electrical resistance, thermopower, magnetic susceptibility, magnetization, and temperature coefficients of linear expansion and relative elongation ΔL/L measured by the method of dilatometry) in the temperature range of 2-870 K. This work has established the effects of quenching on the microstructure, magnetic state, critical temperatures, and specific features of thermoelastic martensitic transformations in the alloy. [ABSTRACT FROM AUTHOR]

The phase composition, structure, magnetic and thermoelastic martensitic transformations, and physical properties (magnetic susceptibility, magnetization, electric resistivity) in multicomponent magnetic Ni 50 − xCo xMn 29Ga 21 alloys (with a Co content of x = 0, 1, 2, 3, and 10 at %) exhibiting a magnetically controlled shape memory effect are studied. The critical temperatures of the magnetic transitions and thermoelastic martensitic transformations are determined. It is shown that the studied alloys in the austenitic state are substitutional solid solutions based on a quasi-ternary L2 1 superstructure (Ni, Co) 50Mn 29Ga 21. [ABSTRACT FROM AUTHOR]