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In this work, the electronic structure and magnetic properties of GdNiSi have been investigated within the framework of theoretical DFT + U method. The antiferromagnetic ordering of the Gd moments was obtained as the ground state, whereas Ni and Si have negligible magnetic moments. An antiferromagnetic-to-ferromagnetic transition was found when GdNiSi is doped with Al in our theoretical calculations. The antiferromagnetic-to-ferromagnetic transition takes place in the Gd sublattice, the magnetic moments at the Gd ions remain the same but the type of magnetic ordering changes. It was found that even at concentrations as low as , the ferromagnetic ordering in the Gd sublattice is more favorable in total energy as the ground state which can be ascribed to the shortening of Gd–Gd distances and the oscillating behavior of the Ruderman–Kittel–Kasuya–Yosida interaction in the Al-doped compositions. The electronic structure demonstrates significant changes in the vicinity of the localized Gd 4f states that confirms the presence of the antiferromagnetic-to-ferromagnetic transition using our theoretical results for Al in good agreement with the previous experimental magnetic results. [ABSTRACT FROM AUTHOR]

The intermetallic compounds GdFe1−xCrxSi, x = 0–0.8, GdFe1−xVxSi, x = 0–0.4, and GdFe1−xNixSi, x = 0–0.4 with a tetragonal CeFeSi (P4/nmm) structure type have been synthesized. The Curie temperature, TC, sharply increases from 130 K to 255 K and 250 K for the GdFe1−xCrxSi and GdFe1−xVxSi compounds and decreases to 104 K for GdFe1−xNixSi. Within the framework of the model of effective d–f exchange interaction in R3¯d intermetallics, these changes in TC can be caused by the corresponding changes in the density of states. The electronic structure, magnetic moments and types of magnetic orderings of the GdFe1−xTxSi, T = Cr, V, Ni intermetallic compounds were calculated using the DFT+U theoretical method. For the GdFe1−xNixSi system, the transformation of a ferromagnet with the composition x = 0 into an antiferromagnet with the composition x = 0.3 was established experimentally and using first-principles calculations. The correlation of the ferromagnetic or antiferromagnetic type of the magnetic state in the GdFe1−xNixSi compounds with the value of the lattice parameter c to greater or less than the critical value c = 6.72 Å for the GdCoSi antiferromagnet has been experimentally established. The magnetic structures of the antiferromagnets GdFe0.7Ni0.3Si and GdCoSi were found to be different. GdFe0.7Ni0.3Si is characterized by a collapse in the magnetocaloric effect via a change in the isothermal magnetic entropy ΔSM(TC). The compounds GdFe0.4Cr0.6Si with −ΔSM(TC) = 2.37 J kg−1 K−1 at TC = 255 K and RC = 82.07 J kg−1 and GdFe0.7V0.3Si with −ΔSM(TC) = 2.06 J kg K−1 at TC = 250 K and RC = 96.02 J kg−1 in a field changing to 17 kOe could be of practical interest due to the TC being close to room temperature. [ABSTRACT FROM AUTHOR]

In this paper, we present the calculation results of the electronic structure and optical spectrum and an experimental study of the optical properties of Heusler alloys Mn2 –xFe1 +xAl (x = –0.5, 0, 0.5, 1). An anomalous for metallic systems behavior of the optical conductivity of alloys in the IR region of the spectrum was found: the absence of Drude growth and a high level of interband absorption. This behavior is shown to be determined by the features of the electronic structure: the Fermi level is located in the region of high density of states that is formed by the d states of Mn and Fe. [ABSTRACT FROM AUTHOR]

The intermetallic compounds GdFe 1- x Cr x Si, x = 0-0.8, GdFe 1- x V x Si, x = 0-0.4, and GdFe 1- x Ni x Si, x = 0-0.4 with a tetragonal CeFeSi ( P4/nmm ) structure type have been synthesized. The Curie temperature, T C , sharply increases from 130 K to 255 K and 250 K for the GdFe 1- x Cr x Si and GdFe 1- x V x Si compounds and decreases to 104 K for GdFe 1- x Si. Within the framework of the model of effective d-f exchange interaction in x Si. Within the framework of the model of effective d-f exchange interaction in R 3̄d intermetallics, these changes in T C can be caused by the corresponding changes in the density of states. The electronic structure, magnetic moments and types of magnetic orderings of the GdFe 1- x T x Si, T = Cr, V, Ni intermetallic compounds were calculated using the DFT+U theoretical method. For the GdFe 1- x Ni x Si system, the transformation of a ferromagnet with the composition x = 0 into an antiferromagnet with the composition x = 0.3 was established experimentally and using first-principles calculations. The correlation of the ferromagnetic or antiferromagnetic type of the magnetic state in the GdFe 1- x Ni x Si compounds with the value of the lattice parameter c to greater or less than the critical value c = 6.72 Å for the GdCoSi antiferromagnet has been experimentally established. The magnetic structures of the antiferromagnets GdFe 0.7 Ni 0.3 Si and GdCoSi were found to be different. GdFe 0.7 Ni 0.3 Si is characterized by a collapse in the magnetocaloric effect via a change in the isothermal magnetic entropy Δ S M ( T C ). The compounds GdFe 0.4 Cr 0.6 Si with -Δ S M ( T C ) = 2.37 J kg -1 K -1 at T C = 255 K and R C = 82.07 J kg -1 and GdFe 0.7 V 0.3 Si with -Δ S M ( T C ) = 2.06 J kg K -1 at T C = 250 K and RC = 96.02 J kg -1 in a field changing to 17 kOe could be of practical interest due to the T C being close to room temperature.