Search Results (5)

Three high-entropy Sm(Eu,Gd)Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2O₃ perovskite solid solutions were synthesized using the usual ceramic technology. The XRD investigation at room temperature established a single-phase perovskite product. The Rietveld refinement with the FullProf computer program in the frame of the orthorhombic Pnma (No 62) space group was realized. Along with a decrease in the V unit cell volume from ~224.33 ų for the Sm-based sample down to ~221.52 ų for the Gd-based sample, an opposite tendency was observed for the unit cell parameters as the ordinal number of the rare-earth cation increased. The average grain size was in the range of 5–8 μm. Field magnetization was measured up to 30 kOe at 50 K and 300 K. The law of approach to saturation was used to determine the M_s spontaneous magnetization that nonlinearly increased from ~1.89 emu/g (Sm) up to ~17.49 emu/g (Gd) and from ~0.59 emu/g (Sm) up to ~3.16 emu/g (Gd) at 50 K and 300 K, respectively. The M_r residual magnetization and H_c coercive force were also determined, while the SQR loop squareness, k magnetic crystallographic anisotropy coefficient, and H_a anisotropy field were calculated. Temperature magnetization was measured in a field of 30 kOe. ZFC and FC magnetization curves were fixed in a field of 100 Oe. It was discovered that the T_mo magnetic ordering temperature downward-curve decreased from ~137.98 K (Sm) down to ~133.99 K (Gd). The spin glass state with ferromagnetic nanoinclusions for all the samples was observed. The <D> average and D_max maximum diameter of ferromagnetic nanoinclusions were calculated and they were in the range of 40–50 nm and 160–180 nm, respectively. The mechanism of magnetic state formation is discussed in terms of the effects of the A-site cation size and B-site poly-substitution on the indirect superexchange interactions. Full article

Magnetic and magnetocaloric properties of a spin-1 Heisenberg diamond cluster with two different coupling constants are investigated with the help of an exact diagonalization based on the Kambe’s method, which employs a local conservation of composite spins formed by spin-1 entities located in opposite corners of a diamond spin cluster. It is shown that the spin-1 Heisenberg diamond cluster exhibits several intriguing quantum ground states, which are manifested in low-temperature magnetization curves as intermediate plateaus at 1/4, 1/2, and 3/4 of the saturation magnetization. In addition, the spin-1 Heisenberg diamond cluster may also exhibit an enhanced magnetocaloric effect, which may be relevant for a low-temperature refrigeration achieved through the adiabatic demagnetization. It is evidenced that the spin-1 Heisenberg diamond cluster with the antiferromagnetic coupling constants $J_1$/$k_{\mathrm{B}}$ = 41.4 K and $J_2$/$k_{\mathrm{B}}$ = 9.2 K satisfactorily reproduces a low-temperature magnetization curve recorded for the tetranuclear nickel complex [Ni${}_4$($\mu$-CO${}_3$)${}_2$(aetpy)${}_8$](ClO${}_4$)${}_4$ (aetpy = 2-aminoethyl-pyridine) including a size and position of intermediate plateaus detected at 1/2 and 3/4 of the saturation magnetization. A microscopic nature of fractional magnetization plateaus observed experimentally is clarified and interpreted in terms of valence-bond crystal with either a single or double valence bond. It is suggested that this frustrated magnetic molecule can provide a prospective cryogenic coolant with the maximal isothermal entropy change $-\mathsf{\Delta }{S}_M=10.6$ J·K${}^{-1}$·kg${}^{-1}$ in a temperature range below 2.3 K. Full article

Recently, we proposed an approximate expression for the liquid–vapor saturation curves of pure fluids in a temperature–entropy diagram that requires the use of parameters related to the molar heat capacity along the vapor branch of the saturation curve. In the present work, we establish a connection between these parameters and the ideal-gas isobaric molar heat capacity. The resulting new approximation yields good results for most working fluids in Organic Rankine Cycles, improving the previous approximation for very dry fluids. The ideal-gas isobaric molar heat capacity can be obtained from most Thermophysical Properties databases for a very large number of substances for which the present approximation scheme can be applied. Full article

The present work exhibits the effects of Sn addition on the magnetic properties and microstructure of FeCoNi(CuAl)_0.8Sn_x (0 ≤ x ≤ 0.10) high-entropy alloys (HEAs). The results show all the samples consist of a mixed structure of face-centered-cubic (FCC) phase and body-centered-cubic (BCC) phase. The addition of Sn promotes the formation of BCC phase, and it also affects the shape of Cu-rich nano-precipitates in BCC matrix. It also shows that the Curie temperatures (T_c) of the FCC phase and the saturation magnetization (M_s) of the FeCoNi(CuAl)_0.8Sn_x (0 ≤ x ≤ 0.10) HEAs increase greatly while the remanence (B_r) decreases after the addition of Sn into FeCoNi(CuAl)_0.8 HEA. The thermomagnetic curves indicate that the phases of the FeCoNi(CuAl)_0.8Sn_x (0 ≤ x ≤ 0.10) HEAs will transform from FCC with low T_c to BCC phase with high T_c at temperature of 600–700 K. This work provides a new idea for FeCoNi(CuAl)_0.8Sn_x (0 ≤ x ≤ 0.10) HEAs for their potential application as soft magnets to be used at high temperatures. Full article

In order to investigate behavior of magnetic field-induced reverse martensitic transformation for Ni-Co-Mn-Sb, magnetization experiments up to a static magnetic field of 18 T and a pulsed magnetic field of 40 T were carried out. In the thermomagnetization curves for Ni₄₁Co₉Mn₃₉Sb₁₁ alloy, the equilibrium transformation temperature T₀ was observed to decrease with increasing applied magnetic field, μ₀H, at a rate of dT₀/dμ₀H = 4.6 K/T. The estimated value of entropy change evaluated from the Clausius-Clapeyron relation was about 14.1 J/(K·kg), which was in good agreement with the value obtained by differential scanning calorimetric measurements. For the isothermal magnetization curves, metamagnetic behavior associated with the magnetic field-induced martensitic transformation was observed. The equilibrium magnetic field, μ₀H₀ = (μ₀H_Af + μ₀H_Ms)/2, of the martensitic transformation tended to be saturated at lower temperature; that is, transformation arrest phenomenon was confirmed for the Ni-Co-Mn-Sb system, analogous with the Ni(Co)-Mn-Z (Z = In, Sn, Ga, Al) alloys. Temperature dependence of the magnetic field hysteresis, μ₀H_hys = μ₀H_Af − μ₀H_Ms, was analyzed based on the model for the plastic deformation introduced by the dislocations. The behavior can be explained by the model and the difference of the sweeping rate of the applied magnetic field was well reflected by the experimental results. Full article