Peculiarities of the electronic and magnetic characteristics in Co2YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys close to the half-metallic ferromagnets and spin gapless semiconductors

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)

NONLINEAR VOLT-AMPPER CHARACTERISTICS OF THE SPECIALTIME TUNGLED TEMPERATURE MONOCRYSTALS AT LOW TEMPERATURES AND IN STRONG MAGNETIC FIELDS

The magnetoresistance and the current-voltage characteristics of tungsten single crystals with a resistivity ratio ρ300K/ρ4.2K = 80000 at T = 4,2 K in fields up to 150 kOe were investi-gated. As a result of the research, nonlinear VACs were found in the magnetoresistance of tungsten crystals under the conditions of SSE. It is suggested that the possible cause of the observed nonlinearities is the effect of phonon generation by supersonic drift of charge car-riers near the conductor surface.Работа выполнена в рамках государственного задания ФАНО России (тема «Спин», № 01201463330) при частичной поддержке Правительства Российской Федерации (постановление № 211, контракт № 02.A03.21.0006) и гранта № 14.Z50.31.0025 Министерства образования и науки РФ

Strong changes in electronic transport and magnetic properties of Co2 YSi Heusler alloys at Y-component variation

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, 18-02-00739Government Council on Grants, Russian Federation: 02.Ural Branch, Russian Academy of Sciences, UB RAS: 18-10-2-37АААА-А18-118020290129-5This 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)

Magnetic order and electronic transport properties in the Mn3Al compound: The role of the structural state

Electronic transport and magnetic properties of bulk and rapid melt quenched samples of the Mn3Al Heusler alloy were studied. A correlation between the magnetic and structural states was established. For a cast sample, there is no ferromagnetic moment, and the behavior of the magnetic susceptibility (break at low temperatures and the Curie-Weiss law with high values of the paramagnetic Curie temperature) indicates a frustrated antiferromagnetic state. At the same time, for a rapid melt quenched sample, a ferrimagnetic state is observed with a moment close to compensation. The results of measurements of the electrical resistivity and the Hall effect evidence as well in favor of the implementation of these magnetic states. © 2023 Elsevier B.V.Ministry of Education and Science of the Russian Federation, Minobrnauka: 122021000033-2, 122021000036-3; Russian Science Foundation, RSF: 22-22-00935Synthesis of the alloy and RMQ tapes, studies of electron transport and magnetic properties were supported by Russian Science Foundation (project No. 22-22-00935 ).The structure studies were carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (themes “Structure” No. 122021000033-2 and “Spin” No. 122021000036-3). Synthesis of the alloy and RMQ tapes, studies of electron transport and magnetic properties were supported by Russian Science Foundation (project No. 22-22-00935). Authors thank P.B. Terentyev, D.A. Shishkin, V.N. Neverov for help and valuable discussions

Electronic transport features of MoTe2caused by quenching

The electro- and magnetoresistivity of MoTe2 single crystals before and after quenching were measured at temperatures from 1.8 to 300 K and in magnetic fields of up to 9 T. It was demonstrated that quenching can lead to strong changes in values of the electro-and magneresistivity studied as well as in their temperature and field dependences. The peculiarities of these electronic transport characteristics changes were studied in detail. © Published under licence by IOP Publishing Ltd.The research was carried out within the state assignment of the Ministry of Education and Science of the Russian Federation (theme “Spin”, No. АААА-А18-118020290104-2), supported in part by RFBR (Project No. 17-52-52008) and the Government of Russian Federation (Decree No. 211, Contract No. 02.A03.21.0006)

Electronic, magnetic and galvanomagnetic properties of Co-based Heusler alloys: Possible states of a half-metallic ferromagnet and spin gapless semiconductor

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. © 2021 Author(s).The work was performed within the framework of the state assignment of the Ministry of Science and Higher Education of Russia (the themes “Spin,” No. AAAA-A18-118020290104-2-2 and “Quantum” No. AAAA-A18-118020190095-4) with partial support from the RFBR (projects No. 18-02-00739 and 20-32-90065) and the Government of the Russian Federation (Decree No. 211, Contract No. 02.A03.21.0006)

Features of the electroresistivity, magnetic and galvanomagnetic characteristics in Co2MeSi Heusler alloys

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)

Electrical, magnetic and galvanomagnetic properties of Mn-based Heusler alloys

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: 18-02-00739Government Council on Grants, Russian Federation: 02, 211Ministry of Science and Higher Education of the Russian Federation: AAAA-A18-1118020190095-4Ural Branch, Russian Academy of Sciences, UB RAS: 18-10-2-37The 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)

Magnetic and thermal properties of alloys close in composition to the spin gapless semiconductor Mn2CoAl

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 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

Electronic properties of WTe2 and MoTe2 single crystals

WTe2 and MoTe2 single crystals were grown, and their electrical resistivity in the temperature range from 80 K to 300 K, optical properties at room temperature in the spectral range of 0.17-5.0 eV were studied as well as theoretical calculations of the electronic structure were performed. It is shown that the temperature dependence of the electrical resistivity of orthorhombic WTe2 has a metallic type with resistivity value of (0.5-1) mOhmcm, while hexagonal MoTe2 has a semiconductor one and resistivity value (0.5-1) Ohmcm, which is three orders of magnitude larger than the resistivity of WTe2. Optical properties indicated that there is no contribution from free carriers in the entire spectral range studied. The calculated densities of the electronic states of MoTe2 and WTe2 showed the presence of a bunch of the molybdenum and tungsten electronic states in a wide energy interval with strong admixing of tellurium states. In the WTe2 compound, the larger number of the electronic states is located near the Fermi energy, characterizing a more metallic state in this compound as compared to MoTe2. © Published under licence by IOP Publishing Ltd.Government Council on Grants, Russian Federation: 02, 211Russian Foundation for Basic Research, RFBR: 17-52-52008Ministry of Education and Science of the Russian Federation, Minobrnauka: АААА-А18-118020190098-5The 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 and theme “Electron” No. АААА-А18-118020190098-5), supported in part by RFBR (Project No. 17-52-52008) and the Government of Russian Federation (Decree No. 211, Contract No. 02.A03.21.0006)