Rare Earth Intermetallic Compounds Research Articles

Incommensurate antiferromagnetism in a pure spin system via cooperative organization of local and itinerant moments.

Materials with strong correlations are prone to spin and charge instabilities, driven by Coulomb, magnetic, and lattice interactions. In materials that have significant localized and itinerant spins, it is not obvious which will induce order. We combine electrical transport, X-ray magnetic diffraction, and photoemission studies with band structure calculations to characterize successive antiferromagnetic transitions in GdSi. GdSi has both sizable local moments and a partially nested Fermi surface, without confounding contributions from orbital effects. We identify a route to incommensurate order where neither type of moment dominates, but is rooted in cooperative feedback between them. The nested Fermi surface of the itinerant electrons induces strong interactions between local moments at the nesting vector, whereas the ordered local moments in turn provide the necessary coupling for a spin-density wave to form among the itinerant electrons. This mechanism echoes the cooperative interactions between electrons and ions in charge-density-wave materials, and should be germane across a spectrum of transition-metal and rare-earth intermetallic compounds.

Possible multigap superconductivity and magnetism in single crystals of superconducting La2Pt3Ge5and Pr2Pt3Ge5

We herein describe our investigation of the superconducting and magnetic properties of the rare-earth ternary germanide intermetallic compounds La${}_{2}$Pt${}_{3}$Ge${}_{5}$ and Pr${}_{2}$Pt${}_{3}$Ge${}_{5}$. Single crystals of La${}_{2}$Pt${}_{3}$Ge${}_{5}$ and Pr${}_{2}$Pt${}_{3}$Ge${}_{5}$ were synthesized using the high-temperature metal flux method. Both types of crystal formed in a U${}_{2}$Co${}_{3}$Si${}_{5}$-type orthorhombic structure (space group $Ibam$). La${}_{2}$Pt${}_{3}$Ge${}_{5}$ showed the onset of superconducting phase transition at ${T}_{c}$ $=$ 8.1 K, which, to the best of our knowledge, is the highest ${T}_{c}$ of all the $R$${}_{2}$$M$${}_{3}$$X$${}_{5}$ ($R$ $=$ rare-earth elements, $M$ $=$ transition metal, and $X$ $=$ $s\text{\ensuremath{-}}p$ metal) superconductors, and from the specific heat data, it was found to have multigap superconductivity. Pr${}_{2}$Pt${}_{3}$Ge${}_{5}$ showed both a superconducting phase transition at ${T}_{c}$ $=$ 7.8 K and two antiferromagnetic transitions at ${T}_{N1}$ $=$ 3.5 K and ${T}_{N2}$ $=$ 4.2 K, which indicates the coexistence of superconductivity and magnetism. However, the correlation between the superconductivity and the magnetism was too weak to be observed. In its normal state, Pr${}_{2}$Pt${}_{3}$Ge${}_{5}$ revealed strong magnetic anisotropy, probably due to the crystalline electric field effect.

ChemInform Abstract: Physical Properties of Single‐Crystalline Magnetic Intermetallic Compounds

AbstractReview: 43 refs.

Ultrafast quasiparticle dynamics in the heavy-fermion compound YbRh2Si2

Understanding strongly correlated rare-earth intermetallic compounds requires knowledge of the nature of the fermionic quasiparticles in states near the Fermi level ${E}_{\mathrm{F}}$. We report on a pump-probe experiment using femtosecond time- and angle-resolved photoemission spectroscopy to determine lifetimes of hot quasiparticles in the heavy-fermion compound YbRh${}_{2}$Si${}_{2}$. An unoccupied band with electronlike dispersion and a band bottom 0.2 eV above ${E}_{\mathrm{F}}$ was identified at $\overline{\ensuremath{\Gamma}}$, in agreement with band structure calculations for the subsurface region. Hot quasiparticle lifetimes from 30 to 80 fs were found for energies between 0.4 and $0.1$ eV above ${E}_{\mathrm{F}}$. These lifetimes generally follow the typical monotonous increase towards ${E}_{\mathrm{F}}$, in agreement with earlier studies on Yb and Rh elemental metals. However, at normal emission the lifetimes at around 0.2 eV exceed this trend by about $+20$ fs. This difference decreases with increasing photoemission angle and can be assigned to the particular band that is probed in YbRh${}_{2}$Si${}_{2}$. Potential microscopic scenarios are discussed.

Temperature-induced itinerant electron metamagnetism in intermetallic RCo3 compounds

The phenomenon of temperature-induced itinerant electron metamagnetism in a zero external field is of the same nature as the widely investigated metamagnetic transitions induced by magnetic fields (external or internal). Recently, temperature-induced itinerant metamagnetism was discovered in the rareearth intermetallic RCo3 compounds. Systematic investigations of the RCo3 series made it possible to determine many specific features of this new phenomenon and to formulate criteria to reveal such transitions in other magnetic materials as well. This paper presents a brief review of the existing works and original results on temperature-induced itinerant-electron metamagnetism in substituted RCo3 compounds.

Anisotropic magnetic behavior of PrAg 2Ge 2—a crystal field study

A crystal field (CF) analysis of the experimental, single crystal magnetic susceptibility data (300–1.8 K) along and perpendicular to the [0 0 1] axis, of the Ag based rare earth intermetallic compound PrAg 2Ge 2, has been carried out for the first time, thus yielding first reliable set of CF parameters for the system. The susceptibility feature at 12 K is possibly due to CF effects rather than the magnetic order as proposed earlier. This removes the issue of the transition temperature being too large to scale properly with the de Gennes factor. We have used the set of CF parameters to find the Stark energies of the ground state and the excited states together with their corresponding eigenvectors, and the thermal variation of the magnetic specific heat. Possible explanation of the absence of magnetic ordering of the Pr sublattice and the nature of variation of the CF parameters with the substitution of transition-metal ion in PrAg 2Ge 2 is studied and discussed in relation to PrAu 2Ge 2. All computations have been carried out using the intermediate coupling scheme including the J-mixing.

A first-order magnetic phase transition near 15 K with novel magnetic-field-induced effects in Er5Si3

We present magnetic characterization of a binary rare-earth intermetallic compound Er5Si3, crystallizing in Mn5Si3-type hexagonal structure, through magnetization, heat capacity, electrical resistivity and magnetoresistance measurements. Our investigations confirm that the compound exhibits two magnetic transitions with decreasing temperature, the first one at 35 K and the second one at 15 K. The present results reveal that the second magnetic transition is a disorder-broadened first-order transition, as shown by thermal hysteresis in the measured data. Another important finding is that, below 15 K, there is a magnetic-field-induced transition with a hysteretic effect with the electrical resistance getting unusually enhanced at this transition and the magnetoresistance is found to exhibit intriguing magnetic-field dependence, indicating novel magnetic phase coexistence phenomenon. It thus appears that this compound is characterized by interesting magnetic anomalies in the temperature–magnetic-field phase diagram.

Successive Transition in Rare-earth Intermetallic Compound GdNiC2

In GdNiC2, the magnetic state is investigated under the high magnetic fields and the low temperatures. We find the intermediate phases, in which the magnetization value is close to a half of the full moment, and the successive transition in the phase boundary between the antiferromagnetic, the metamagenetic, and the paramagnetic phases. The mechanism of the intermediate phase is discussed.

Magnetic ordering and crystal field effects in theR2Ir3Sn5(R=La–Nd, Gd–Tm) system

We report on the detailed magnetic properties of polycrystalline ternary rare-earth intermetallic stannide compounds $R$${}_{2}$Ir${}_{3}$Sn${}_{5}$ ($R$ $=$ La--Nd, Gd--Tm). Except for La${}_{2}$Ir${}_{3}$Sn${}_{5}$, all the other compounds of $R$${}_{2}$Ir${}_{3}$Sn${}_{5}$ ($R$ $=$ Ce--Nd, Gd--Tm) crystallize in the orthorhombic Y${}_{2}$Rh${}_{3}$Sn${}_{5}$(Cmc2${}_{1}$) type structure. La${}_{2}$Ir${}_{3}$Sn${}_{5}$ crystallizes in the U${}_{2}$Co${}_{3}$Si${}_{5}$ type orthorhombic crystal structure with the space group Ibam. Transport and magnetization measurements were done from 1.8 to 300 K and the heat-capacity measurement was done from 2 to 30 K. We found from the magnetic measurements that Ce${}_{2}$Ir${}_{3}$Sn${}_{5}$ is a Kondo system, which undergoes an antiferromagnetic ordering at 2.9 K, while no magnetic ordering was observed in Pr${}_{2}$Ir${}_{3}$Sn${}_{5}$ and Nd${}_{2}$Ir${}_{3}$Sn${}_{5}$ down to 1.8 K. The higher rare earths from Gd--Tm of this series exhibit magnetic ordering below 10 K. Crystal field analysis was done on both the magnetic susceptibility and heat capacity to find the crystal field level schemes. From the detailed magnetic measurements, we found that the magnetic ordering temperature deviates from the expected de Gennes scaling, which indicates that the RKKY interaction needs to be modified, including the crystal field effects, to account for this deviation.

Coupling of field-induced spin fluctuations and spin-density wave in intermetallic CeAg2Ge2

We report on experimental evidence for a coupling between the magnetic-field-induced fluctuations of correlated Ce ions coinciding with the discontinuous movement of the underlying spin-density wave in the intermetallic rare-earth compound CeAg${}_{2}$Ge${}_{2}$. The measurements performed using neutron scattering and magnetic Gruneisen ratio methods suggest that the coupling is onset at $H=2.7$ T and $T\ensuremath{\le}3.8$ K and persists to the lowest measurement temperature of $\ensuremath{\simeq}$0.05 K. These measurements suggest that the spin fluctuations can affect the intrinsic properties of the system.

First-principles calculations on temperature-dependent elastic constants of rare-earth intermetallic compounds: YAg and YCu

We present the temperature-dependent elastic constants of two ductile rare-earth intermetallic compounds YAg and YCu with CsCl-type B2 structure by using a first-principles approach. The elastic moduli as a function of temperature are predicted from the combination of static volume-dependent elastic constants obtained by the first-principles total-energy method with density-functional theory and the thermal expansion obtained by the first-principles phonon calculations with density-functional perturbation theory. The comparison between our calculated results and the available experimental data for Ag and Cu provides good agreements. In the calculated temperature 0–1000 K, the elastic constants of YAg and YCu follow a normal behavior with temperature that those decrease with increasing temperature, and satisfy the stability conditions for B2 structures. The Cauchy pressure for YAg and YCu as a function of temperature is also discussed, and our results mean that YAg and YCu become more ductile while increasing temperature.

First-principle study on structural, elastic and electronic properties of rare-earth intermetallic compounds: TbCu and TbZn

Structural, elastic and electronic properties of TbCu and TbZn have been studied using the full-potential augmented plane waves plus local orbital (APW+lo) within density functional theory (DFT). Results on elastic properties are obtained using both the local density approximation (LDA) and generalized gradient approximation (GGA) for exchange correlation potentials. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. Young’s modulus, shear modulus, Poisson ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and Grüneisen parameters have been calculated. Taking elastic moduli (calculated from first-principle approach) as reference values at 0K, temperature variation of elastic moduli has also been calculated using electrostatic and Born repulsive potentials and taking interactions up to next nearest neighbours. Calculated structural, elastic and other parameters are consistent with available data. From electronic calculations, it has been found that electronic conductivity in TbCu and TbZn is attributed to 3d-orbital electrons of Cu and Zn.

First-principles phonon calculations of thermodynamic properties for ductile rare-earth intermetallic compounds

The thermodynamic properties of ductile rare-earth intermetallic compounds YAg and YCu with CsCl-type B2 structure have been studied by performing density-functional theory (DFT) and density-functional perturbation theory (DFPT). To judge that our computational method is reasonable, NiAl has also been investigated in comparisons with experimental data and previous theoretical results. Phonon dispersions and density of states are studied, and it is found that the density of states is mostly composed of Y states both in YAg and YCu at high frequencies. The temperature dependence of various quantities such as the thermal expansion, the isothermal bulk modulus, and the heat capacity is computed under the quasi-harmonic approximation (QHA), and the variation features of these quantities are discussed in detail. From these results, we demonstrate that the intermetallics with better ductility have larger thermal expansions.

Influence of magnetic fluctuations in the magnetocaloric effect on rare-earth intermetallic compounds

A theoretical model including both crystal-field and exchange interactions that considers the effect of magnetic fluctuations is developed to evaluate the temperature dependence of the isothermal magnetic entropy changes in ferromagnetic rare-earth-based intermetallic compounds. The Green's functions are derived from their equation of motion. The magnetic moment correlation functions are determined beyond the random phase approximation by incorporating a measure of magnetic spontaneous fluctuations in a way that ensures self-consistency with regard to the fluctuation-dissipation theorem. In particular, the exact magnitude of the entropy change without magnetic moment fluctuations depends on the ratio of both the crystal-field first- and the crystal-field third-order magnetic susceptibilities at the Curie temperature, ${T}_{C}$. These theoretical predictions are compared with experimental data on cubic RM${}_{2}$ ($\mathrm{R}=\mathrm{rare}\mathrm{ }\mathrm{earth}$ and $\mathrm{M}=\mathrm{Al}$ and Ni) compounds, where the principal crystal-field and exchange parameters are well known.

Impurities in Magnetic Materials Studied by PAC Spectroscopy

Perturbed gamma-gamma angular correlation (PAC) spectroscopy is a precise and highly efficient tool to follow the temperature dependence of local magnetic fields in any material. Its resolution and efficiency does not depend on temperature and therefore can measure local fields at low as well as high temperature with the same accuracy. Due its versatility in using different probe nuclei it can sense the local magnetic fields at different sites in the crystalline structure of materials. In this review, important results obtained with PAC spectroscopy are shown in two classes of materials: transition metal and transition-metal based compounds and rare earth elements and rare-earth-element based compounds using mainly three different probe nuclei: 111Cd, 181Ta and 140Ce. PAC spectroscopy has contributed to the systematic study of the magnetic hyperfine field in impurities in matrices of Fe, Co and Ni as well as in transition-metal based Heusler alloys. It has also provided important contribution to the investigation of magnetism in rare-earth elements and intermetallic compounds. An still open issue concerning the local fields in metallic magnetic compounds and elements is the exchange interaction between the magnetic ions of the host and a dilute magnetic impurity, which acts as a defect in the magnetic lattice. PAC spectroscopy has been contributing to study this problem with success. Also shown in this review is the crucial role of ab-initio first principle calculations in the interpretation of PAC results.

Long-time variation of magnetic structure in rare-earth intermetallic compounds

Long-time variations of magnetic structure have been studied by means of time-resolved neutron scattering measurements in two kinds of non-diluted uniform magnets, PrCo2Si2 and TbNi2Si2. These materials show commensurate (C) to incommensurate (IC) magnetic transitions below Néel temperature. When a sample is cooled to the low temperature C-phase, magnetic Bragg scattering signals from the C and the IC phases coexist and then their intensity vary with time. These characteristics are similar to those of the previously studied material CeIr3Si2. However, the temperature ranges in which clear time variations exist are much narrower in the present materials.

Magnetic Properties of Non-Stoichiometric <i>R</i>Ni<sub>2</sub>Mn<sub>x</sub> (<i>R</i> = Tb, Dy) Compounds

Structure and magnetic properties of non-stoichiometric rare earth intermetallic compounds TbNi2Mnx and DyNi2Mnx x have been studied. It was found that for the compositions with x ≤ 1 the alloys retain the single-phase cubic structure despite the fact that the rare earth-to-3d metal ratio changes from 1:2 to 1:3. Magnetic measurements revealed that the Mn alloying leads to a substantial growth of the Curie temperature with a maximum at x ~ 0.5. At low temperatures the magnetization reversal of the Mn-containing samples is characterized by a considerable hysteresis caused by pinning of narrow domain walls by the structure defects. The observed experimental data are discussed within the assumption on a local distortion of the crystal electric field and the formation of a non-collinear magnetic structure of the rare earth sublattice.

Physical properties of single‐crystalline magnetic intermetallic compounds

AbstractSingle crystals on a macroscopic scale exhibit microscopic periodicity on an atomic level, which enables us to investigate their intrinsic physical properties and to optimize their functional properties. We have grown various kinds of magnetic single crystals of intermetallic compounds for fundamental research and for applications. In this, much effort has been focused on the growth conditions to satisfy the different requirements, especially for crystals that are hard to grow. In this paper, we review some selected results on various single crystals grown in our institute and illustrate the importance of single‐crystal growth for research and application. Several intrinsic magnetic properties, including magnetocrystallographic anisotropy, spin reorientations, and magnetostriction have been investigated in detail on single crystals of rare‐earth intermetallic compounds. The internal stress induced in crystals of magnetic shape‐memory alloys is utilized to reorient the martensitic microstructure for maximizing the output strain. Combining the self‐flux method with magnetic elevating Czochraski cold‐crucible growth technology, a deeply undercooled environment was achieved to enable (Tb,Dy)Fe2 single crystals to be grown. Some research works on crystal growth, such as solidifying theories, growth dynamics, and phase diagrams, are also discussed.

Magnetic properties and structure of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi2Mn x (0 ≤ x ≤ 1.5)

Crystal structure, magnetization, coercive force, magnetic susceptibility, and anisotropic magnetostriction of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi2Mn x (0 ≤ x ≤ 1.5) have been studied. The samples with x ≤ 1 have an fcc structure, whereas TbNi2Mn1.25 has a rhombohedral structure of the PuNi3 type. It has been found that the magnetic ordering temperature increases sharply when manganese is added. As the Mn concentration grows, the magnetization and the magnetostriction decrease monotonically, while the coercive force increases. The experimental data obtained have been interpreted on the assumption that a partial substitution of manganese for terbium in TbNi2Mn x leads to local distortions of the crystal field acting on Tb ions, to the appearance of a local uniaxial random anisotropy, and to the formation of a noncollinear magnetic structure in the terbium sublattice.

ChemInform Abstract: Novel Permanent Magnetic Materials

Materials for high-performance permanent magnets must have a high Curie temperature, a large spontaneous magnetization and strong uniaxial magnetocrystalline anisotropy. Binary rare earth iron intermetallics are deficient in one or more of these respects. New series of rare-earth intermetallic compounds may be generated from existing series by a process known as gas-phase interstitial modification, whereby interstitial atoms such as nitrogen or carbon are introduced into the structure by reaction of a powder of the intermetallic with an appropriate gas. The interstitials occupy sites adjacent to the rare earth, thereby creating a crystal field that reflects the new local symmetry. They also expand the lattice, which greatly enhances the Fe-Fe exchange interactions, and may increase slightly the iron moment. These effects are discussed in detail for four systems, R2Fe17N3-δ, R2Fe17C3-δ R(Fe11 Ti)N1-δ and R(Fe11 Ti)C1-δ (R = rare earth), all of which include compounds with potential for making new parmanent magnets.