Intermediate valence of CeNi2Al3 compound and its evidences: Theoretical and experimental approach

We present measurements of magnetic, transport and electronic properties obtained for polycrystalline CeNi2Al3 intermetallic compound. Magnetic susceptibility χ(T) was investigated in the range from 2 to 700 K, and its behavior is characteristic of a compound with unstable valence, varying between Ce3þ and Ce4þ. In the temperature range down to 2 K there was no trace of magnetic order, no anomalies in the temperature dependence of the specific heat were found. The Sommerfeld coefficient extracted from the linear term of the heat capacity takes a value of γ ¼ 21 mJ/(mol K2). The dependence of S(T) is linear up to about 25 K, which is symptomatic of a thermopower in the Fermi’s liquid regime. The structure of satellites in the Ce(3d) electron spectrum obtained by the X-ray photoelectron spectroscopy (XPS) method indicates that the states of Ce(4f) are of mixed valence character. Analysis of Ce(3d) states based on Gunnarsson-Sch€onhammer theory shows that the energy of hybridization of Ce(4f) states with a conduction band is about 78 meV. For more detailed information about electronic states the fully relativistic band structure was calculated within the density functional theory (DFT) for the first time. Below Fermi’s energy, the density of states is mainly formed by Ni(3d) states hybridized with Ce(4f) ones

Development of magnetic properties during annealing of Hf₂Co₁₁B amorphous alloy

Influence of heat treatment on magnetic properties of amorphous Hf₂Co₁₁B alloy was investigated. Hard magnetic phase, characterized by high magnetic anisotropy, appears during crystallization. The highest coercive field equal to 1.86 kOe, was obtained for sample annealed in third crystallization stage. Longer heat treatment at T_{a} = 650°C leads to decrease in coercive field, which can be the result of excess of the HfCo₃B₂ phase volume fraction and additionally eutectoid transformation of hard magnetic phase into soft magnetic Co₂₃B₆ and fcc-Co. Decrease of volume fraction of hard phase is confirmed by the remanence ratio m_{r}. Value of m_{r}, for T_{a} = 650°C, is decreasing with annealing time from 0.4 to 0.27 for 30 min and 120 min, respectively. The magnetocrystalline anisotropy constant K₁ increases from 2.23 Merg/cm³ for the amorphous ribbon to 15.84 Merg/cm³ for the sample annealed at 650°C for 30 min

Activation Energies of Crystallization in Amorphous RMn4.5Ge4.5Fe1.5Al1.5RMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5} (R = La, Y, Dy) Alloys

The effective activation energies, characteristic crystallization temperatures and enthalpies of amorphous $RMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ (R = Y, La, Dy) alloys produced using melt-spinning technique were investigated by differential scanning calorimetry. X-ray diffraction measurements were performed for as-quenched and annealed samples. The crystalline structure of annealed $YMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ and $DyMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ alloys was determined as orthorhombic $TbFe_6Sn_6$-type with Cmcm (63) space group. The alloy with Y appears as a more useful non-magnetic analogue for $DyMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ than the La-based alloy. The differential scanning calorimetry curves for Dy- and Y-based alloys also exhibit similar thermal behavior. The effective activation energies $E_a$ were determined using the Kissinger approach and high values up to 778±74 kJ/mol for La-based sample were established. The comparison of Y-, La-, and Dy-based alloys suggests improvement of thermal stability with the increase in rare-earth element atomic radius in the glassy $RMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ systems

Activation Energies of Crystallization in Amorphous RMn 4.5

The effective activation energies, characteristic crystallization temperatures and enthalpies of amorphous $RMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ (R = Y, La, Dy) alloys produced using melt-spinning technique were investigated by differential scanning calorimetry. X-ray diffraction measurements were performed for as-quenched and annealed samples. The crystalline structure of annealed $YMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ and $DyMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ alloys was determined as orthorhombic $TbFe_6Sn_6$-type with Cmcm (63) space group. The alloy with Y appears as a more useful non-magnetic analogue for $DyMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ than the La-based alloy. The differential scanning calorimetry curves for Dy- and Y-based alloys also exhibit similar thermal behavior. The effective activation energies $E_a$ were determined using the Kissinger approach and high values up to 778±74 kJ/mol for La-based sample were established. The comparison of Y-, La-, and Dy-based alloys suggests improvement of thermal stability with the increase in rare-earth element atomic radius in the glassy $RMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ systems

Critical Behavior near the Ferromagnetic to Paramagnetic Phase Transition in Y₈Co₆₂B₃₀ Amorphous Alloy

The Y₈Co₆₂B₃₀ amorphous alloy is a collinear ferromagnet. The Arrott plot, the Kouvel-Fisher method, critical isotherm analysis and magnetic field dependence of maximum magnetic entropy changes were the main analytical tools used to determine the nature of the ferromagnetic/paramagnetic phase transition. Values of critical exponents (β, γ, and δ) were calculated and were convergent with those characteristic for mean-field model. It suggests that long range ferromagnetic interactions are playing main role in investigated alloy and the phase transition was confirmed to be of a second order according to the Banerjee criterion

Crystallisation of Amorphous Y50Cu42Al8Y_{50}Cu_{42}Al_8 Alloy

Amorphous $Y_{50}Cu_{42}Al_8$ ribbon was prepared by melt-spinning technique on the Cu wheel. The crystallisation process was analysed by differential scanning calorimetry and X-ray diffraction. Differential scanning calorimetry curves characterising two crystallisation stages of $Y_{50}Cu_{42}Al_8$ alloy were measured in non-isothermal dynamic mode at different heating rates. Activation energies of both steps of crystallisation process were acquired by the Kissinger method and are equal to 570± 56 and 290±29 kJ/mol for the first and second stage, respectively. By annealing the ribbon at a given temperature for various times the nanocrystalline phase grains of the sizes of about 40 nm in diameter were created. The influence of the annealing temperature on the grain size evolution was also examined

Semi-Empirical Modelling of Glass Forming Ranges for Y-Co-Si System

Glass forming abilities of a ternary Y-Co-Si system were determined on the basis of combined semi-empirical Miedema's and geometric models. The enthalpy of amorphous and solid solution phases formation, along with the mismatch entropy and GFA parameter, were analysed to indicate compositions with the highest ability for the amorphization. The large atomic radii difference between constituents, especially Y and Si, is the deciding factor of GFA. Compositions ranged between $Y_{33}Si_{67}$ and $Y_{45}Si_{55}$ are the best glass formers

Crystallization Processes of R4.5Fe77B18.5R_{4.5}Fe_{77}B_{18.5} (R = Pr, Nd) Amorphous Alloys

The amorphous alloys $R_{4.5}Fe_{77}B_{18.5}$ (R=Pr, Nd) were prepared by melt-spinning technique under argon atmosphere on a cooper wheel rotating with surface velocity of 25 m·$s^{-1}$. The ribbons have been investigated by means of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Temperatures of crystallization for $Pr_{4.5}Fe_{77}B_{18.5}$, measured at the heating rate 20 K/min, are equal $T_{x1}$=591°C for the first exothermic effect and $T_{x2}$=603°C for the second one (for $Nd_{4.5}Fe_{77}B_{18.5} T_{x1}$=594°C and $T_{x2}$=633°C). In the amorphous ribbons the crystallization of $Fe_{3}B$ phase in the first step, followed by the crystallization of $Pr_{2}Fe_{23}B_{3}$ and $Nd_{2}Fe_{23}B_{3}$, was observed. Both later phases appear in the process of recrystallization, immediately after $Fe_{3}B$ formation