Electronic properties and electronic structure of Co2YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys

Abstract

Energy gap parameters can vary significantly in X2YZ Heusler alloys [1], where Y-elements are 3d-transition metals and Z-components are s- and p-elements. Therefore, changes in different physical properties, especially, in electronic and optical characteristics are observed. Some features may indicate conditions close to half-metallic ferromagnets (HMFs) [2] and spin gapless semiconductors (SGSs) [3]. Such compounds are promising materials for spintronics because they can possess almost 100% spin polarization of charge carriers.HMFs hold an energy gap near the Fermi level for the current carriers with spin down, while its absence for current carriers with spin up. In turn, SGSs are like HMFs for the spin projection down, however, for the opposite spin direction, the gap is being zero [2, 3].Thus, the aim of the work is to follow the changes in the electronic transport, optical properties of the Co2YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys system experimentally, and to compare the results obtained with the electronic band structure calculation, to establish their interconnection and suggest possible proximity to HMF- and/or SGS-states in the Co2YSi system.According to the data of X-ray structural analysis, all compounds are found to be ordered in the L21 structure. The electrical resistivity was measured in a wide temperature range using a PPMS setup. The field and the temperature dependences of the magnetic properties being studied too on the SQUID magnetometer. The coefficients of the normal and anomalous Hall Effect were found. The values of current carrier concentration and their mobility were estimated. Results of optical measurements showed good agreement with electronic band structure calculation. Besides, the correlation between the changes in these electronic, optical characteristics, and the coefficient of the current carrier spin polarization depending on the number of valence electrons are observed, which may point to the possible states of the HMF or SGS in this system of Heusler alloys.The work was performed within the framework of the state assignment of the Ministry of Science and High Education of Russia (the themes “Spin”, No. AAAA-A18-118020290104-2-2 and “Electron” No. AAAA-A18-118020190098-5) with partial support from the RFBR (project No. 20-32-90065), and the Government of the Russian Federation (Decree No. 211, Contract No. 02.A03.21.0006). **