arXiv subjects

Zbigniew Śniadecki

Publications and source records attributed to Zbigniew Śniadecki.

3 recordsLinked to original sources

arXiv2026

Emergence of ferromagnetic state due to structural disorder in pseudo-binary Ce(Fe0.9Co0.1)2 compound

The changes in magnetic properties of Ce(Fe0.9Co0.1)2 compound with increasing disorder are discussed in the paper. Homogeneous alloys are known to undergo the phase transition from ferromagnetic to antiferromagnetic state accompanied by the structural distortion of the cubic Laves C15 phase into the rhombohedral one. Various stimuli, like the structural disorder, or applied magnetic field, can force the emergence of ferromagnetism at low temperatures. We initially introduced the structural disorder using rapid quenching. Further changes were made by severe plastic deformation. The presence of a ferromagnetic phase in a low-temperature region is reported here and accompanies the deterioration of a first-order phase transition. We show, based on electronic calculations, that the structural motifs arising from various distortions of the initial MgCu2-type structure, caused by the partial replacement of Fe with Co atoms, are characterized by stable antiferromagnetic order. This neglects simple structural distortions as the source of ferromagnetism. The presence of a strongly defective structure understood as a topologically disordered volume, reduced the fraction transformed from a ferromagnetic to an antiferromagnetic state. Therefore, a strong reduction of isothermal entropy changes was also observed, as it decreased from 1.94 Jkg-1K-1 and -1.43 Jkg-1K-1 (Δμ0H = 4 T) to 0.30 Jkg-1K-1 and -0.96 Jkg-1K-1 for antiferromagnetic-ferromagnetic and ferromagnetic-paramagnetic transition, respectively.

cond-mat.mtrl-sci↗

arXiv2025

Normal and inverse magnetocaloric effects in structurally disordered Laves phase Y$_{1-x}$Gd$_{x}$Co$_{2}$ (0 $\leq$ x $\leq$ 1) compounds

Magnetic and magnetocaloric properties of Y$_{1-x}$Gd$_{x}$Co$_{2}$ compounds, where x = 0.2, 0.4, 0.6, 0.8 and 1.0, were investigated experimentally and theoretically. Crystal structures were characterized by X-ray diffraction (Rietveld analysis) and investigated samples possess the MgCu$_{2}$-type single phase with Fd-3m space group. Melt-spinning process introduced a chemical and topological disorder, which directly affected the magnetic properties. Refrigerant capacity (RC), strictly connected to the full width at half maximum $δ$TFWHM of the $Δ$S$_M$(T) curve and the maximum of magnetic entropy changes $Δ$S$_{Mpk}$(T)(T,$Δ$H), increases from 29 to 148 J/kg with replacement of Y by Gd atoms from x = 0.2 to x = 0.8. RC and $δ$TFWHM indicate the presence of disorder. Temperature dependences of magnetic entropy change $Δ$S$_M$(T,$Δ$H) and RC were measured in as-quenched and annealed state for Y$_{0.4}$Gd$_{0.6}$Co$_{2}$. This particular composition was chosen for detailed investigation mainly due to its Curie point (T$_C$ = 282 K), which is close to the room temperature. After isothermal annealing ($τ_a$ = 60 min, Ta = 700$^o$C) RC decreased from 122 to 104 J/kg, which clearly indicates the homogenization of the heat treated sample. Furthermore, observed inverse magnetocaloric effect is associated with the presence of antiferromagnetically coupled Gd and Co magnetic moments. The phase transition temperature increases with increasing Gd content from 74 to 407 K for Y$_{0.8}$Gd$_{0.2}$Co$_{2}$ and GdCo2, respectively. Within the FPLO-LDA DFT method, the non-magnetic ground state for YCo$_{2}$ and the magnetic ground state for GdCo$_{2}$ are predicted in agreement with experiment. The dependence of calculated total and species-resolved magnetic moments on Gd concentration reasonably agrees with available experimental data.

cond-mat.mtrl-sci↗

arXiv2019

Electronic specific heat coefficient and magnetic properties of Y(Fe$_{1-x}$Co$_x$)$_2$ Laves phases: a combined experimental and first-principles study

We investigated experimentally and computationally the concentration dependence of electronic specific heat coefficient $γ$ in Y(Fe$_{1-x}$Co$_x$)$_2$ pseudobinary Laves phase system. The experimentally observed maximum in $γ$($x$) around the magnetic phase transition was interpreted within the local density approximation (LDA) combined with the virtual crystal approximation (VCA). To explain the formation of the observed maximum, we analyzed theoretically the dependence of the magnetic energy, magnetic moments, densities of states, and Fermi surfaces on the Co concentration. Furthermore, we carried out the calculations of density of states at the Fermi level as a function of fixed spin moment. The calculated Co concentration at which $γ$ takes the maximum value ($x_{\mathrm{max-LDA-VCA}}=0.91$) stays in good agreement with the measured value ($x_{\mathrm{max-expt}} = 0.925$). We conclude that the observed maximum in $γ(x)$ results from the presence of the sharp DOS peak in the vicinity of the Fermi level.

cond-mat.mtrl-sci↗