Hexagonal Intermetallic Compounds Research Articles

Effects of Ge addition on the structure, mechanical and magnetic properties of (CoCrFeNi)100-xGex high-entropy alloys

Alloying non-metallic elements can not only change the structure of alloys, but also tailor the mechanical and physical properties. The microstructure, mechanical and magnetic properties of (CoCrFeNi)100-xGex (molar ratio, x = 0 ∼ 33) high-entropy alloys (HEAs) have been systematically studied in this paper. The experimental results show that the (CoCrFeNi)100-xGex HEAs transform from a face-centered cubic (FCC) to a body-centered cubic (BCC) solid solution when 10 ≤ x ≤ 25, and a hexagonal intermetallic compound (IM) formed at x = 33. Tensile measurement revealed that the strength and plasticity of the alloy were enhanced simultaneously with Ge addition in the single FCC region (x ≤ 10), a decrease in ductility but sharp increase of strength was found in the alloys when the BCC phase starts to appear. Theoretical calculations and magnetic hysteresis loop measurements show that the alloys transform gradually from a paramagnetic to a ferromagnetic state at room temperature.

Resistivity and magnetoresistance properties of R2NiSi3 (R = Gd, Dy, Ho, Er, Tm) compounds

The resistivity and magnetoresistance behaviour of the hexagonal intermetallic compounds R2NiSi3(R = Gd, Dy, Ho, Er, and Tm) are reported here. All the studied polycrystalline compounds exhibit metallic behaviour along with additional magnetic anomalies at low temperatures. A well-defined resistivity minima is observed in Gd2NiSi3and Dy2Ni0.87Si2.95at a temperature much higher than their respective magnetic transition temperatures. The anomaly has been ascribed to the charge carrier localization caused by magnetic precursor effect. Magnetic field induced crossover from positive to negative magnetoresistance (MR) behaviour associated with antiferromagnetic ground state is evidenced for Gd2NiSi3and Er2NiSi3in the low temperature region. Although Tm2Ni0.93Si2.93does not exhibit any long range magnetic order down to 2 K, a sudden drop in resistivity behaviour is observed below ~10 K. Presence of short range magnetic correlation observed in a wide temperature range, much beyond their respective magnetic ordering temperatures, has been argued to be responsible for achieving finite negative MR for all the compounds. A subtle resemblance between the observed transport anomalies and the magnetic properties of these systems have been discussed.

Effect of Au Doping on Elastic, Thermodynamic, and Electronic Properties of η-Cu6Sn5 Intermetallic

The effects of substitution of Au for Cu on the elastic, thermodynamic, and electronic properties of hexagonal η-Cu6Sn5 intermetallic compound (IMC) are investigated by first-principles calculations. The results show that Au atoms preferentially occupy Cu4 or Cu3 site to form η-Cu5Au1Sn5 or η-Cu4Au2Sn5 IMC, respectively. Doping Au in η-Cu6Sn5 IMC forms a more stable thermodynamic structure than pure phase. The ductility of η-Cu6Sn5 IMC increases after substitution of Au for Cu. However, doping Au weakens the Young’s modulus, shear modulus, hardness, and Debye temperature of η-Cu6Sn5 IMC. The results for the charge density difference, total density of states, and partial density of states show that doping Au atoms can stabilize the structure of η-Cu6Sn5 IMC.

Magnetocaloric properties of cluster glass compound Pr2Ni0.95Si2.95

In this work, we report the magnetocaloric properties of a hexagonal intermetallic compound Pr2Ni0.95Si2.95 that exhibits spin cluster glass behaviour below 3.3 K. At lower temperature, the compound undergoes magnetic field induced metamagnetic transition beyond 5 kOe applied field value as inferred from the temperature dependence of magnetization at various fields as well as isothermal magnetization measurements. The temperature dependence of magnetic entropy change (−ΔSM) has been calculated from the magnetization data and the maximum value is found to be 7.9 J/kg-K for a magnetic field change of 70 kOe. Interestingly, although the compound does not undergo any long range magnetic ordering, it exhibits considerable magnetocaloric effect in a temperature region much above the spin freezing due to the presence of short range magnetic correlation that persists up to much higher temperature. The suppression of short range interaction with the application of magnetic field has been argued to be responsible for such magnetic entropy change and adiabatic temperature change over a large temperature scale.

Pressure Effect on Elastic Constants and Related Properties of Ti₃Al Intermetallic Compound: A First-Principles Study.

Using first-principles calculations based on density functional theory, the elastic constants and some of the related physical quantities, such as the bulk, shear, and Young’s moduli, Poisson’s ratio, anisotropic factor, acoustic velocity, minimum thermal conductivity, and Debye temperature, are reported in this paper for the hexagonal intermetallic compound TiAl. The obtained results are well consistent with the available experimental and theoretical data. The effect of pressure on all studied parameters was investigated. By the mechanical stability criteria under isotropic pressure, it is predicted that the compound is mechanically unstable at pressures above 71.4 GPa. Its ductility, anisotropy, and Debye temperature are enhanced with pressure.

Baromagnetic Effect in the Hexagonal Mn3Sn System

The magnetic behaviors influenced by the hydrostatic pressure in the polycrystalline hexagonal Mn3Sn intermetallic compound are briefly reported. The crystalline structure of Mn3Sn is determined to be hexagonal with lattice parameters $a = b = 5.674$ (6) A and $c = 4.533$ (6) A by means of the powder X-ray diffraction and the subsequent Rietveld refinement. Two distinct transitions can be observed from the M(T) curves in the range of 150-450 K. During the cooling process, Mn3Sn sample first changes into a triangular antiferromagnetic (AFM) state with weak ferromagnetism at the Neel temperature of ~412 K, and then, it further transforms to a spiral AFM spin arrangement over a broad temperature range from 260 to 180 K at ambient pressure. With the application or the increase of hydrostatic pressures, this triangular to spiral AFM transition occurs at higher temperatures, while the magnetization of triangular AFM phase increases significantly. Such a phenomenon can be explained by the fact that the hydrostatic pressure compresses the sample and shortens the Mn–Mn separation, and thus, the moments of Mn will deviate from their ideal 120° configuration to their easy axis in the basal plane. The variations of transition temperature and maximum magnetization with applied hydrostatic pressure confirm the incremental instability of the triangular AFM arrangement under pressure.

Specific features of the electronic structure and spectral characteristics of the Gd5Si3 compound

The electronic structure and optical properties of the hexagonal intermetallic compound Gd5Si3 are investigated. The spin-polarization calculation of the band spectrum is performed in the local spin density approximation, taking account for the strong electron correlations in the 4 f shell of a Gd ion (LSDA + U method). Optical constants of the compound in the wavelength range of 0.22–15 μm are determined by the ellipsometry technique and some spectral characteristics are calculated. The frequency dependence of optical conductivity in the light quantum absorption region is analyzed on the basis of the calculated electron density of states.

Electronic structure and optical properties of the Pr5Ge3 compound

The electronic structure and optical properties of the hexagonal intermetallic compound Pr5Ge3 have been studied. The spin-polarization calculations of the band spectrum have been performed in the approximation of local electron density with allowance for strong electron correlations in 4f shell of the rareearth ion. In the wavelength range λ = 0.22–15 µm, the optical constants of the compound have been measured by the ellipsometric method, and a number of spectral and electronic characteristics have been determined. The experimental dependence of the optical conductivity in the region of quantum absorption of light have been interpreted based on the results of calculating the density of electronic states.

Low-temperature magnetic properties ofNpNi5

We present the result of an extended experimental characterization of the hexagonal intermetallic Haucke compound NpNi$_{5}$. By combining macroscopic and shell-specific techniques, we determine the 5$f$-shell occupation number $n_f$ close to 4 for the Np ions, together with orbital and spin components of the ordered moment in the ferromagnetic phase below T$_C$ = 16 K ($\mu_{S}$ = -1.88~$\mu_{B}$ and $\mu_{L}$ = 3.91~$\mu_{B}$). The apparent coexistence of ordered and disordered phases observed in the M\"{o}ssbauer spectra is explained in terms of slow relaxation between the components of a quasi-triplet ground state. The ratio between the expectation value of the magnetic dipole operator and the spin magnetic moment ($3\langle T_{z}\rangle/ \langle S_{z}\rangle$ = +1.43) is positive and large, suggesting a localized character of the 5$f$ electrons. The angular part of the spin-orbit coupling ($\langle\vec{\ell}\cdot\vec{s}\rangle$ = -5.55) is close to the value of -6.25 calculated for trivalent Np ions in intermediate coupling approximation. The results are discussed against the prediction of first-principle electronic structure calculations based on the spin-polarized local spin density approximation plus Hubbard interaction, and of a mean field model taking into account crystal field and exchange interactions.

Antiferromagnetic ordering and metamagnetism in PrCuSi

A variety of physical properties measured on the hexagonal rare-earth intermetallic compound PrCuSi are presented. We provide compelling evidence for antiferromagnetic ordering at TN = 5.1 K in this compound, in contrast to the former claim of ferromagnetic ordering at 14 K. The antiferromagnetic order is, however, found to be unstable in applied magnetic fields, becoming ferromagnetic beyond a metamagnetic transition at a field of 0.7 T at 2 K. It is argued that the magnetism in PrCuSi has the ingredients of a tricritical phase transition at the intersection of paramagnetism, ferromagnetism, and antiferromagnetism.

Hydrogen Ordering in Hexagonal Intermetallic AB5Type Compounds

Hydrogen Ordering in Hexagonal Intermetallic AB₅Type Compounds

Magnetic structure of Nd 7Ni 3

The magnetic structure of a hexagonal intermetallic compound Nd 7Ni 3 has been studied by the neutron diffraction measurements. The Rietveld analysis was carried out to refine the structural and magnetic parameters. The refined propagation vector is Q = (0 0 0.32(2)) to describe the ferrimagnetic structure at 2.0 K. The magnetic moment of the Nd atom is 2.00(1), 2.09(1), 2.09(1) μ B for the sites I, II and III, respectively. The magnetic moment at the site I has the conical structure with the cone angle 22.00(1)°. The refined initial relative phase is 39.43(3)° for sites I and II and 41.43(5)° for sites II and III, respectively.

Low-temperature specific heat and resistivity studies in the [formula omitted] compounds

The specific heat study of the hexagonal intermetallic compound CeNi 5 revealed a substantial Sommerfeld coefficient of the linear electronic term γ = 40 mJ / mol K 2 . When substituting Cu instead of Ni, the electronic term is no longer linear and the low-temperature enhancement of the electronic term becomes apparent. With the increasing Cu concentration the enhanced γ reaches 46, 95 and 700 mJ / mol K 2 for x = 0.3 , 0.4 and 0.5, respectively, in zero magnetic field. When further increasing the Cu concentration a broad peak develops on the c / T vs. T plot below T = 2 K which can be described by a quasi-doublet with the splitting of the energy levels Δ ≈ 4 K . The low-temperature electronic specific heat of the Ce ( Ni 1 - x Cu x ) 5 compounds and its behaviour in magnetic fields is discussed in terms of possible Ce-valence fluctuations.

Magnetocaloric effect in theRNi5(R=Pr, Nd, Gd, Tb, Dy, Ho, Er) series

In this paper, the magnetocaloric effect in the hexagonal intermetallic compounds belonging to the $R{\mathrm{Ni}}_{5}$ series was calculated using a Hamiltonian including the crystalline electrical field, exchange interaction, and the Zeeman effect. Experimental work was performed and the two thermodynamics quantities, namely, isothermal entropy change and adiabatic temperature change were obtained for polycrystalline samples, using heat capacity measurements, and compared to the theoretical predictions.

The influence of high pressure on the structural and magnetic properties of Y2Fe17−x M x (M=Si, Al; x=1.7) compounds

The influence of high pressure on the crystal structure of the hexagonal intermetallic compounds Y2Fe17, Y2Fe15.3Al1.7, and Y2Fe15.3Si1.7 is investigated by neutron diffraction for the first time. It is shown that, under high pressure, the crystal lattice undergoes an isotropic contraction. A correlation of the changes in the Curie temperature with the distance between iron atoms in the dumbbell positions under pressure is revealed. The effect of pressure on the Y2Fe17 compound is examined at low temperatures. It is found that the magnetostriction in this compound is suppressed under high pressure.

Magnetic order in R 2Ni 17 intermetallics: a neutron-diffraction investigation

The crystal and magnetic structures of hexagonal intermetallic compounds of the type R 2Ni 17 with R=Y, Tb, Dy, Ho and Er have been investigated by neutron powder diffraction at 20 and 200 K. The crystal structures at 200 K, which is above the magnetic ordering temperature for these compounds, have been refined and show that they crystallize in the hexagonal Th 2Ni 17 structure (space group P6 3/mmc). The magnetic structure at 20 K has a magnetic propagation vector k → =0 and consists of a ferrimagnetic alignment of R and Ni moments. At 20 K, compounds with R=Tb, Dy and Ho are collinear ferrimagnets with moments aligned in the basal plane of the hexagonal unit cell, whilst the compound with R=Er is an axial collinear ferrimagnet. The low-temperature magnitudes of the R moments at 2b and 2d sites are markedly different, with an almost free ion value at the 2b site, whilst the 2d site moment is substantially reduced from its free ion value.

Magnetic and Electrical Properties of R7Rh3(R=Gd, Tb, Dy, Ho, Er and Y)

The electric resistivity and magnetic susceptibility have been measured for hexagonal intermetallic compounds R 7 Rh 3 (R=Gd, Tb, Dy, Ho, Er and Y). At low temperature, these compounds except Y 7 R...

Structure of nu-Al(80.61)Cr(10.71)Fe(8.68), a giant hexagonal approximant of a quasicrystal determined by a combination of electron microscopy and X-ray diffraction

Nu-Al(80.61)Cr(10.71)Fe(8.68), P6(3)/m (No. 176), a = 40.68 (7), c = 12.546 (1) A, V = 17,983 (8) A3, atoms/cell = 1184.56, Dx = 3.518 g cm(-3), lambda(Mo K alpha) = 0.71069 A, mu = 5.032 mm(-1), F(000) = 18,433, T = 293 K, final R = 0.075 for 3854 reflections with Fo > 4sigma(Fo). The [001] high-resolution electron-microscopic image of the nu-AlCrFe phase clearly shows similar local characteristics to those given by the complex icosahedral cluster found in somewhat smaller hexagonal approximant structures, such as kappa-Al76Cr18Ni6 [a = 17.674 (3), c = 12.516 (3) A; Sato et al. (1997). Acta Cryst. C53, 1531-1533; Marsh (1998). Acta Cryst. B54, 925-926] and lambda-Al(4.32)Mn [a = 28.382 (9), c = 12.389 (2) A; Kreiner & Franzen (1997). J. Alloys Compd. 261, 83-104]. Using the known atomic distribution of this icosahedral cluster in the kappa and lambda phases as the starting point, the structure of the nu phase, a hexagonal intermetallic compound with probably the largest a parameter, was solved by X-ray single-crystal diffraction using direct methods. As in kappa and lambda phases, almost all TM (transition metal) atoms in the complex icosahedral cluster are icosahedrally coordinated. However, contrary to the lambda structure in which about 98% of the TM atoms have icosahedral-coordination, the TM atoms in the v structure also form capped pentagonal prisms in the region between these complex icosahedral clusters, yielding an average icosahedral coordination of about 70% for TM atoms. After rapid solidification, the v phase occurs together with a decagonal quasicrystal with a periodicity of about 12.5 A along its tenfold axis and thus also consists of six layers, two flat ones each sandwiched between two puckered layers in mirror reflection, stacked along the c axis.

Magnetic ordering in MnB 2: an ab initio study

We present an ab initio study of different possible magnetic states of the hexagonal intermetallic compound MnB 2 employing the augmented spherical wave method. The calculations show that the ground state of MnB 2 is antiferromagnetically ordered. The calculated magnetic moment of Mn is close to 2 μ B for both the antiferromagnetic (AF) and the ferromagnetic (FM) states. This result is in contradiction to the earlier experiments which classified MnB 2 as an itinerant ferromagnet. This experimental conclusion was drawn from magnetization and susceptibility measurements which find a small saturated moment (∼0.2 μ B/Mn) and a high Rhodes–Wohlfarth ratio. Our calculation shows that the density of states exhibits a d-band splitting of the Mn subband of about 2 eV and that the spin-up d-subband is placed well below (∼1 eV) the Fermi energy implying a certain degree of localization of manganese d-states. It appears that the calculated effective moment is in good agreement with the value obtained experimentally from the Curie–Weiss fit to the paramagnetic susceptibility. In order to resolve this contradiction we suggest a spin canting structure which could be responsible for the small FM component found in the experiment.

High-field studies at the Tsukuba magnet laboratories

A 40 T class hybrid magnet system, built at the National Research Institute for Metals, Japan, has been used to measure the transport properties of organic conductors, η-MoO11, etc. A Fourier-transform spectrometer in the milli- to submillimeter range has been developed using a lamellar grating, and has been used in magneto-optical studies of the spin-Peierls oxide CuGeO3. Fermi surfaces have been investigated extensively using a 16 T magnet with a dilution refrigerator, and de Haas-van Alphen oscillations were clearly observed in the mixed state, as well as in the normal state for YNi2B2C Crystals. Magnetization measurements have been performed on the hexagonal intermetallic compound RPd2Al3 using pulsed magnetic fields. The present status of the high-field magnets and the experimental results obtained at the NRIM are described.