Rare Earth Intermetallic Compounds Research Articles

Determination of the crystal field levels in TmV2Al20

Analysis of inelastic neutron scattering data recorded for the rare earth intermetallic compound TmV2Al20 yields a cubic crystal field Hamiltonian with parameters x = −0.63(1) and W = +0.43(1) K (Lea, Leask & Wolf notation). This result is supported by a strong electron paramagnetic resonance signal that is consistent with magnetic splitting of the first excited (Γ5(1)) state. Using this crystal field Hamiltonian, single crystal magnetisation and specific heat data are then interpreted in terms of a model that involves partial Al flux substitution of an approximately 10% depleted Tm “cage” site.

On-Surface Synthesis of Graphene Nanoribbons on Two-Dimensional Rare Earth-Gold Intermetallic Compounds.

Here, we demonstrate two reliable routes for the fabrication of armchair-edge graphene nanoribbons (GNRs) on TbAu2/Au(111), belonging to a class of two-dimensional ferromagnetic rare earth-gold intermetallic compounds. On-surface synthesis directly on TbAu2 leads to the formation of GNRs, which are short and interconnected with each other. In contrast, the intercalation approach-on-surface synthesis of GNRs directly on Au(111) followed by rare earth intercalation-yields GNRs on TbAu2/Au(111), where both the ribbons and TbAu2 are of high quality comparable with those directly grown on clean Au(111). Besides, the as-grown ribbons retain the same band gap while changing from p-doping to weak n-doping mainly due to a change in the work function of the substrate after the rare earth intercalation. The intercalation approach might also be employed to fabricate other types of GNRs on various rare earth intermetallic compounds, providing platforms to tailor the electronic and magnetic properties of GNRs on magnetic substrates.

Effect of trace La on microstructure and properties of Cu–Cr–In alloys

The strength and conductivity of Cu–Cr–In alloys with trace La and different processing states were compared. Then, the influence of La on the structure and properties of the Cu–Cr–In alloy and the associated mechanisms were analyzed. The mechanical properties and microstructural evolution of the alloy were investigated via scanning electron microscopy, transmission electron microscopy, and tensile strength measurements. The results showed that the addition of 0.07wt% La to the Cu–Cr–In alloy had the effect of purifying the alloy melt and removing impurities, which improved the electrical conductivity of the alloy. However, the formation of rare earth intermetallic compounds reduced the tensile strength of the Cu–Cr–In–La alloy. After thermomechanical treatment, the Cu–Cr–In–La alloy reached a peak strength of 457 MPa and a conductivity of 85% IACS.

Magnetism and magnetocaloric effect of melt-spun, nanostructured GdAl2

Magnetocaloric effect (MCE) of melt-spun rare earth intermetallic compound GdAl2 (Cubic, MgCu2-type) has been studied. The sample becomes nanostructured upon melt-spinning and the crystallite size obtained from the powder x-ray diffraction data is about 48 nm. A sluggish paramagnetic to ferromagnetic transition occurs at a Curie temperature (TC) of about 136 K. This value is about 30 K lower than the ferromagnetic transition temperature of the arc-melted GdAl2. The maximum isothermal magnetic entropy change (ΔSm) is found to be ∼ −8.3 Jkg−1 K−1 at 133 K for 70 kOe field change around TC. This value is quite comparable to that of bulk sample prepared by arc-melting which is about −8.5 Jkg−1 K−1 at 168 K for the same field change. Thus melt-spinning process results in broadening of the peak in the isothermal magnetic entropy change versus temperature plot without compromising on the magnetocaloric effect.

Low temperature deformation mechanisms of single crystalline intermetallic compound YAg

YAg belongs to the family of B2-type rare earth intermetallic compounds that in polycrystalline form exhibit moderate low temperature ductility. In this work, YAg single crystals have been deformed at low temperatures down to 4 K. The activation parameters and their dependence on stress and temperature, as well as the comparison with the deformation behavior of polycrystalline YAg, indicate that the cutting of forest dislocations is the rate-controlling deformation mechanism, similar to face-centered cubic metals. The results suggest that the low yield stress and high work-hardening rate observed cause the moderate ductility at low temperatures.

Low Temperature Deformation Mechanisms of Single Crystalline Intermetallic Compound Yag

YAg belongs to the family of B2-type rare earth intermetallic compounds that in polycrystalline form exhibit moderate low temperature ductility. In this work, YAg single crystals have been deformed at low temperatures down to 4 K at which significant ductility was observed. The activation parameters and their dependence on stress and temperature, as well as the comparison with the deformation behavior of polycrystalline YAg, indicate that the cutting of forest dislocations is the rate-controlling deformation mechanism, similar to face-centered cubic metals. The results suggest that a low Peierls stress causes the moderate ductility at low temperatures.

Enhanced magnetocaloric effect in undercooled rare earth intermetallic compounds RNi (R = Gd, Ho and Er)

Equiatomic RNi (where R = Gd, Ho and Er) compounds have been prepared by undercooling. Magnetization data confirm ferromagnetic ordering of the samples at 69 K, 35 K and 10 K (TC) respectively. Magnetocaloric effect (MCE) has been estimated in terms of isothermal magnetic entropy change (ΔSm) near TC. The maximum ΔSm value (ΔSmmax) for 50 kOe field change is about −18 Jkg-1K−1, −20 Jkg-1K−1 and −30 Jkg-1K−1 respectively near TC for the undercooled RNi (R = Gd, Ho and Er) compounds. The ΔSmmax value is more than that obtained for the same compounds prepared by arc-melting and melt-spinning techniques. The observed enhancement in MCE of the undercooled samples could be due to the improved purity that results in faster change of magnetization around the magnetic transition. Thus undercooling rare earth intermetallics and alloys seems to be an attractive, alternative method to synthesize magnetocaloric materials.

Structure and Magnetic Properties of RIn2.9Co0.1 (R = La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Lu)

AbstractRIn2.9Co0.1 (R = rare earth) intermetallic compound has been synthesized, and its structure and magnetic properties have been investigated using X‐ray diffraction, scanning electron microscopy with energy dispersive spectrum and magnetic measurement. RIn2.9Co0.1 crystallizes in cubic AuCu3‐type structure for R = heavy rare earths, and a small amount of R(In, Co)2 metaphase separates from RIn2.9Co0.1 for R = light rare earth. Rietveld's structural refinement confirms that R(In, Co)2 metaphase is the isomorphism of hexagonal CaIn2. The lattice parameters of RIn2.9Co0.1 tend to decrease with increasing atomic number of R due to the shrinking effect of atomic radius in rare earth group. The cubic phase can be stabilized in the range of 1.048–1.133 for the effective atomic radius ratio RA and 0.35–0.41 for the electronegativity difference ΔX. The magnetizing process of RIn2.9Co0.1 shows various characteristics with increasing atomic number of rare earth, and the magnetizing curves follow a ferromagnetic model for R = La, a mixed ferromagnetic and paramagnetic model for R = Ce, Pr, Nd, Gd, Tb, Dy. The formation of ferromagnetic characteristics results from the strong spin–spin interaction between R and Co.

Induced magnetism and “magnetic hole” in singlet ground state system PrNi

Abstract The phenomenon of “induced magnetic ordering” for the local magnetic moments with singlet ground state in a periodical lattice is considered for the prototype intermetallic rare-earth compound PrNi ordered ferromagnetically at temperature TC = 21 K. Within the framework of a realistic model the energy dispersion relations are obtained for the magnetic excitations above Tc along the high symmetry directions. The “soft mode” behaviour observed for the acoustic magnetic excitation along (q 0 0) direction is reproduced. The influence of the substitution of isovalent nonmagnetic La for Pr1−xLaxNi on the temperature of ferromagnetic ordering is investigated. The linear decrease of the ordering temperature TC down to zero value in increasing of the La concentration up to x = 0.5 is observed and described by the model.

New ternary aluminides RERh4Al15 (RE = La, Ce, Pr, Sm, Gd)

The aluminum-rich intermetallic rare earth compounds RERh4Al15 (RE = La, Ce Pr, Sm, Gd) were synthesized by arc melting of the elements under an argon atmosphere. The samples were characterized by powder X-ray diffraction which revealed a straight-forward agreement of the synthesized materials with tetragonal space group P42/nmc, NdRh4Al15.37 structure type. The structures of CeRh4Al15 and PrRh4Al15 were refined from single-crystal X-ray diffraction data. CeRh4Al15 is a new correlated electron compound with Kondo interaction. There is no magnetic ordering above 0.05 K despite the localized Ce3+ magnetic moment behaviour near room temperature. The electronic specific heat, magnetic susceptibility and electrical resistivity indicate that the compound may be accidently poised near a magnetic quantum critical point.

Review on the materials and devices for magnetic refrigeration in the temperature range of nitrogen and hydrogen liquefaction

Magnetic refrigeration based on magnetocaloric effect (MCE) has become a promising alternative technique to the traditional gas-compression refrigeration due to its friendly environment and high energy efficiency. In addition to room temperature magnetic refrigeration, this novel technology can be applied at low temperature, especially for the potential applications in gas liquefaction. Therefore, attention has been paid to explore suitable materials with large MCE near the gas liquefaction temperature and develop low temperature magnetic refrigerators. Herein, the typical magnetocaloric materials and prototypes in the temperature range of nitrogen and hydrogen liquefaction are reviewed. Heavy rare earth intermetallic compounds are promising for low temperature magnetic refrigeration due to a low ordering temperature and large magnetic moments. For example, DyFeSi compound shows a large reversible MCE under a low field change of 1 T around TC = 70 K, which is near the liquefaction temperature of nitrogen (77 K). It has been proposed that a composite can be formed by a group of magnetic refrigeration materials with successive transition temperatures and nearly constant MCEs, therefore expanding the range of working temperature desirable for Ericsson-cycle magnetic refrigeration.

Relativistic splitting of surface states at Si-terminated surfaces of the layered intermetallic compoundsRT2Si2(R=rare earth;T=Ir, Rh)

We present an effective model for surface states at the Si-terminated (001) surface of ternary rare earth (R) intermetallic compounds ${\mathit{RT}}_{2}{\mathrm{Si}}_{2}$ with the transition metal element $T$ = Ir or Rh. The model is based on a fully ab initio derivation of the relativistic $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ Hamiltonian and is thereby capable of accurately reproducing the spin polarization of the spin-orbit split surface states, which is very different from the classical Rashba effect. The reliable treatment of spin in our model enables a predictive analysis of the effect of magnetic exchange interaction of the surface-state electrons with ferromagnetically ordered $4f$ moments of the subsurface rare-earth layer in the magnetic phases of the ${\mathit{RT}}_{2}{\mathrm{Si}}_{2}$ compounds.

Raman study of the vibration eigenmodes of CePt5 films on Pt(111)

The surface intermetallic rare-earth compound CePt5 in the range of few unit cells has a high relevance in the field of Kondo- and heavy fermion physics. Besides, it shows an intriguing crystal-lattice development, which is expected to be reflected in its vibration modes. We present a temperature-dependent vibrational frequency- and symmetry analysis by polarized Raman spectroscopy on CePt5 films and for comparison isostructural LaPt5 films. Three CePt5 eigenmodes with characteristic symmetry properties occur with frequencies around 100, 120, and 130 cm−1. By group-theoretical analysis and from the evolution of their intensities they are attributed to the mode of the bulklike CePt5 film and E2- and A1 modes of a symmetry-reduced CePt5 top layer, respectively. Thus, they confirm the model, derived by low-energy electron diffraction, of this material system regarding structure and strain development. The LaPt5 vibration peaks are qualitatively similar. Slight frequency shifts of the latter are mainly attributed to a modified strain development. Finally, an anomalous low-temperature frequency shift occurs for the A1 mode of the CePt5 top layer, which might indicate an interaction with the 4f electron system.

Nanogranular, Melt-Spun Intermetallic Compound SmNi: Magnetocaloric Effect and Large Coercivity

Rare earth intermetallic compound SmNi has been synthesized by melt spinning under argon atmosphere. This sample crystallizes in orthorhombic structure (CrB-type, Space group Cmcm, No. 63) and exhibits texture and nanograin formation. The average crystallite size calculated from powder X-ray diffraction data is ~17 nm. Melt-spun SmNi orders ferromagnetically at ~47 K ( $T_{C}$ ) and this is close to $T_{C}$ of the arc-melted sample. The saturation magnetization value at 10 K is only ~0.24 $\mu _{B}$ /f.u., whereas a large coercivity of ~24 kOe is observed. Isothermal magnetic entropy change, $\Delta S_{m}$ , shows a maximum at $T_{C}$ , of ~−1 J/kg $\cdot$ K, for 50 kOe field change with a relative cooling power value of ~10 J/kg. Small moment of Sm, strong magnetocrystalline anisotropy, complex magnetic structure, and nanograin size all influence the magnetism of melt-spun SmNi.

Theoretical study on the stability, electronic, mechanical, vibrational and thermodynamic properties of rare-earth intermetallic compound Rh3Ce

ABSTRACTThe structural, stability, electronic, mechanical, vibrational and thermodynamic properties of rare-earth intermetallic compound Rh3Ce have been explored systematically by using first-principle calculations. The evaluation of the equilibrium lattice parameters were obtained firstly. Remarkably, the result of calculated unit cell volume, derived by the total energies as a function of volume, is consistent with other results. Next, the values of cohesive energy (Ec), formation enthalpy (ΔH) have verified that Rh3Ce is a stable compound. In addition, the band structure and the total density of states indicate a metallic behaviour. Furthermore, the Mulliken charges were calculated to understand the bonding in Rh3Ce compound. Otherwise, the elastic constants(Cij) as well as other modulus were also calculated to evaluated the mechanical properties of Rh3Ce. Phonon dispersion curves for Rh3Ce were depicted to access the vibrational properties. Finally, the thermodynamic properties of Rh3Ce were summarised range from 0 to 60 GPa, 0 to 1800 K, respectively. We also pointed out that the thermal expansion(α), heat capacity(Cv), entropy(S), Debye temperature(Θ) and Güneisen parameter (γ) change under pressure and temperature.

Features of magnetization behavior in the rare-earth intermetallic compound (Nd0.5Ho0.5)2Fe14B

The crystal-electric field parameters are determined for the (Nd0.5Ho0.5)2Fe14B compound by analyzing experimental magnetization curves obtained in magnetic fields up to 60 T. The values of the crystal-field parameters B20, B40, B60, B44, B64 are 56.3, −73.2, −10.74, −8.9, 0 cm−1 for Nd3+ ion and 312.38, −176.78, 89.2, −88.43, 0 cm−1 for Ho3+ ion. The transition from the ferri-to the field-induced ferromagnetic state has been studied in detail.

Deformation mechanisms of nil temperature ductile polycrystalline B2 intermetallic compound YAg

The most ductile rare earth intermetallic compound, YAg, was subjected to an thermal activation analysis at low temperatures down to 4 K. Evaluation of the activation parameters and their dependence on stress and temperature yields strong indication for forest dislocation cutting as the rate-controlling deformation mechanism, similar to face-centered cubic metals. Surprisingly, nil temperature ductility was observed. Together with results of a detailed TEM analysis of the active slip systems it is concluded that, despite of violating the von Mises criterion for the plastic deformation of polycrystalline materials, a low elastic anisotropy and/or low Peierls stress is responsible for the appreciable ductility at low temperatures. This finding may help to search for other ductile systems in the broad class of intermetallic compounds.

Phase transition of intermetallic TbPt at high temperature and high pressure

Here we present synchrotron-based x-ray diffraction experiments combined with diamond anvil cell and laser heating techniques on the intermetallic rare earth compound TbPt (Pnma and Z = 4) up to 32.5 GPa and ~1800 K. The lattice parameters of TbPt exhibit continuous compression behavior up to 18.2 GPa without any evidence of phase transformation. Pressure–volume data were fitted to a third-order Birch–Murnaghan equation of state with V0 = 175.5(2) Å3, = 110(5) GPa and = 3.8(7). TbPt exhibits anisotropic compression with βa > βb > βc and the ratio of axial compressibility is 2.50:1.26:1.00. A new monoclinic phase of TbPt assigned to the Pc or P2/c space group was observed at 32.5 GPa after laser heating at ~1800 K. This new phase is stable at high pressure and presented a quenchable property on decompression to ambient conditions. The pressure–volume relationship is well described by the second-order Birch–Murnaghan equation of state, which yields V0 = 672(4) Å3, = 123(6) GPa, which is about ~14% more compressible than the orthorhombic TbPt. Our results provide more information on the structure and elastic property view, and thus a better understanding of the physical properties related to magnetic structure in some intermetallic rare earth alloys.

Magnetocaloric effect in textured rare earth intermetallic compound ErNi

Melt-spun ErNi crystallizes in orthorhombic FeB-type structure (Space group Pnma, no. 62) similar to the arc-melted ErNi compound. Room temperature X-ray diffraction (XRD) experiments reveal the presence of texture and preferred crystal orientation in the melt-spun ErNi. The XRD data obtained from the free surface of the melt-spun ErNi show large intensity enhancement for (1 0 2) Bragg reflection. The scanning electron microscopy image of the free surface depicts a granular microstructure with grains of ∼1 μm size. The arc-melted and the melt-spun ErNi compounds order ferromagnetically at 11 K and 10 K (TC) respectively. Field dependent magnetization (M-H) at 2 K shows saturation behaviour and the saturation magnetization value is 7.2 μB/f.u. for the arc-melted ErNi and 7.4 μB/f.u. for the melt-spun ErNi. The isothermal magnetic entropy change (ΔSm) close to TC has been calculated from the M-H data. The maximum isothermal magnetic entropy change, -ΔSmmax, is ∼27 Jkg-1K-1 and ∼24 Jkg-1K-1 for the arc-melted and melt-spun ErNi for 50 kOe field change, near TC. The corresponding relative cooling power values are ∼440 J/kg and ∼432 J/kg respectively. Although a part of ΔSm is lost to crystalline electric field (CEF) effects, the magnetocaloric effect is substantially large at 10 K, thus rendering melt-spun ErNi to be useful in low temperature magnetic refrigeration applications such as helium gas liquefaction.

Development of the active magnetic regenerative refrigerator operating between 77 K and 20 K with the conduction cooled high temperature superconducting magnet

The experimental investigation of an active magnetic regenerative refrigerator (AMRR) operating between 77 K and 20 K is discussed in this paper, with detailed energy transfer analysis. A multi-layered active magnetic regenerator (AMR) is used, which consists of four different rare earth intermetallic compounds in the form of irregular powder. Numerical simulation confirms that the AMR can attain its target operating temperature range. Magnetic field alternation throughout the AMR is generated by a high temperature superconducting (HTS) magnet. The HTS magnet is cooled by a two stage Gifford-McMahon (GM) cryocooler. Helium gas was employed as a working fluid and its oscillating flow in the AMR is controlled in accordance with the magnetic field variation. The AMR is divided into two stages and each stage has a different mass flow rate as needed to achieve the desired cooling performance. The temperature variation of the AMR during the experiment is monitored by temperature sensors installed inside the AMR. The experimental results show that the AMRR is capable of achieving no-load temperature of 25.4 K while the warm end temperature is 77 K. The performance of the AMRR is analyzed by observing internal temperature variations at cyclic steady state. Furthermore, numerical estimation of the cooling capacity and the temperature variation of the AMR are examined and compared with the experimental results.