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The structure and optical properties of the Mn2FeAl Heusler alloy have been investigated. It is shown that the alloy crystallizes into a structure of the β-Mn type. The behavior of the optical conductivity of the alloy, which is anomalous for metallic systems (namely, the absence of a contribution from the intraband absorption and the presence of the intensive interband absorption), is observed in the IR spectral range. It is shown that this behavior is due to the following peculiarities of the electronic structure: the Fermi level is located in the region of a high density of states formed by the d states of Mn and Fe atoms.

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.

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.

Parameters of the energy gap and, consequently, electronic, magnetic and galvanomagnetic properties in different X$_2$YZ 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 Co$_2$YSi (Y = Ti, V, Cr, Mn, Fe) and Co$_2$MnZ 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., 10 pages

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. © 2021 Author(s). The research was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (theme “Spin” No. AAAA-A18-118020290104-2), was supported in part by the Russian Foundation for Basic Research (projects Nos. 18-02-00739 and 20-32-90065) and by the Government of the Russian Federation (decision No. 211, contract No. 02.A03.21.0006). The authors would like to thank D. A. Shishkin and P. B. Terentyev for measuring the magnetic properties of alloys at high temperatures.

A single crystal of a topological Weyl semimetal WTe2 was grown and its electrical resistivity and galvanomagnetic properties (magnetoresistivity and the Hall effect) were investigated in detail in the temperature range from 1.8 K to 300 K and in magnetic fields of up to 9 T. © Published under licence by IOP Publishing Ltd. The research was carried out within the state assignment of Ministry of Education and Science of the Russian Federation (theme “Spin”, No. АААА-А18-118020290104-2), supported in part by RFBR (Project No. 20-32-90069) and the Government of Russian Federation (Decree No. 211, Contract No. 02.A03.21.0006).

The structural and magnetic properties (field dependences of the magnetization in magnetic fields of up to 6 kOe) of thin-film Co2FeAl, and Co2NiSi Heusler alloys grown by pulsed laser deposition on glass and a single-crystalline Al2O3 R-plane substrate at different growth temperatures (20, 280 and 420 °C) were studied. It was found that the stoichiometric composition of the films depends on the substrate temperature during growth and repeats the composition of the target for films grown at low temperatures. The films deposited on a single crystalline Al2O3 substrate have uniaxial magnetic anisotropy in the plane. © Published under licence by IOP Publishing Ltd. This work was partly supported by the state assignment of Minobrnauki of Russia (themes “Spin” No. АААА-А18-118020290104-2), RFBR grants (Nos. 18-32-00686 and 18-02-00739) and the Government of the Russian Federation (state contract No. 02.A03.21.0006).

A topological semimetal PtSn4 single crystal was grown by method of crystallization from a solution in a melt. Then the electrical resistivity and galvanomagnetic properties (magnetoresistivity and the Hall effect) were studied in the temperature range from 4.2 to 80 K and in magnetic fields up to 100 kOe. The optical measurements were carried out at room temperature. The residual resistivity is shown to be low enough and amount to ∼ 0.5 μOhm•cm. The temperature dependence of the electrical resistivity has a metallic type, increasing monotonically with temperature. A sufficiently large magnetoresistance of 750% is observed. The majority carriers are supposed to be holes with a concentration of ∼ 6.8•10 21 cm -3 and mobility of ∼ 1950 cm 2 /Vs at T = 4.2 K as a result of the Hall effect studies. The optical properties of PtSn 4 have features characteristic of "bad" metals. © 2019 Published under licence by IOP Publishing Ltd. This work was partly supported by the state assignment of Russia (theme “Spin” No. АААА-А18-18020290104-2 and theme “Electron” No. АААА-А18-118020190098-5), by the RFBR (project No.17-52-52008) and by the Government of the Russian Federation (state contract No. 02.A03.21.0006).

The Co2 YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys can manifest the properties of half-metallic ferromagnets. These compounds are promising materials for spintronics since almost 100 % spin polarization of charge carriers can be realized at room temperature. We measured the electroresistivity, magnetic and galvanomagnetic properties of the Co2 YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys from 4.2 K to 300 K and in magnetic fields up to 100 kOe. The type, concentration and mobility of charge carriers were estimated. The Y-component variation in the Co2 YSi Heusler alloys is found to affect strongly the number of current carriers and alter the electronic band structure near the Fermi level E F and, consequently, the electronic transport and magnetic properties of the Co2 YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys. © Published under licence by IOP Publishing Ltd. Russian Foundation for Basic Research, RFBR: 18-32-00686, 18-02-00739 Government Council on Grants, Russian Federation: 02. Ural Branch, Russian Academy of Sciences, UB RAS: 18-10-2-37 АААА-А18-118020290129-5 This work was partly supported by the state assignment of Minobrnauki of Russia (themes “Spin” No. АААА-А18-118020290104-2 and “Magnet” No. АААА-А18-118020290129-5), RFBR grants (Nos. 18-32-00686 and 18-02-00739), the Scientific Program of UB RAS (project No. 18-10-2-37) and the Government of the Russian Federation (state contract No. 02.A03.21.0006).

The Hall Effect and magnetization of Heusler alloys Co2YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) were measured at T = 4.2 K and 300 K in magnetic fields of up to 100 kOe as well as the temperature dependence of the electroresistivity from 4.2 to 300 K. The normal and anomalous Hall coefficients, saturation magnetization, residual resistivity, type and concentration of current carriers and their mobility were obtained. It was demonstrated that there is a clear correlation between the electronic and magnetic parameters obtained, depending on the number of valence electrons z, at the transition from Co2TiSi (z=26) to Co2NiSi (z=32). The observed peculiarities of electronic and magnetic parameters may be due to the appearance of the states of the half-metallic ferromagnet and/or spin gapless semiconductor. © Published under licence by IOP Publishing Ltd. This work was carried out as part of the state task of the Russian Ministry of Education and Science (themes “Spin”,No. AAAA-A18-118020290104-2) with partial support from the Russian Foundation for Basic Research (projects Nos. 18-32-00686 and 18-02-00739) and the Government of the Russian Federation (Act No. 211, contract No. 02.A03.21.0006).

Half-metallic ferromagnets and spin gapless semiconductors are promising materials for spintronic devices since a high degree of the spin polarization of charge carriers can be realized in such materials. Spin gapless semiconductors make it possible to combine the properties of half-metallic ferromagnets with semiconductor characteristics and to perform fine tuning of the energy gap value. The Mn2 MeAl (Me = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys can possess such features. We studied the electrical, magnetic and galvanomagnetic properties of the Mn2 MeAl (Me = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys from 4.2 K to 900 K and in magnetic fields up to 100 kOe. The features in the electronic and magnetic properties of Mn2MeAl Heusler alloys were observed, which can be a manifestation of the electronic energy spectrum peculiarities with occurrence of the half-metallic ferromagnet and/or spin gapless semiconductor states. © Published under licence by IOP Publishing Ltd. Russian Foundation for Basic Research, RFBR: 18-02-00739 Government Council on Grants, Russian Federation: 02, 211 Ministry of Science and Higher Education of the Russian Federation: AAAA-A18-1118020190095-4 Ural Branch, Russian Academy of Sciences, UB RAS: 18-10-2-37 The work was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (themes “Spin”, No. AAAA-A18-118020290104-2-2 “Magnet”, No. АААА-А18-118020290129-5 and “Quant”, No. AAAA-A18-1118020190095-4), supported in part by RFBR (projects No. 18-02-00739), the Complex Program of the UB RAS (Project No. 18-10-2-37) and the Government of the Russian Federation (Decree No. 211, Contract No. 02.A03.21.0006).

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. © 2021 Author(s). The research was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (theme “Spin” No. AAAA-A18-118020290104-2), was supported in part by the Russian Foundation for Basic Research (Projects Nos. 18-02-00739 and 20-32-90065) and by the Government of the Russian Federation (decision No. 211, contract No. 02.A03.21.0006).