Rare-earth Intermetallics Research Articles

Phonon softening and atomic modulations in EuAl4

EuAl4 is a rare-earth intermetallic in which competing itinerant and/or indirect exchange mechanisms give rise to a complex magnetic phase diagram, including a centrosymmetric skyrmion lattice. These phenomena arise not in the tetragonal parent structure but in the presence of a charge-density wave (CDW), which lowers the crystal symmetry and renormalizes the electronic structure. Microscopic knowledge of the corresponding atomic modulations and their driving mechanism is a prerequisite for a deeper understanding of the resulting equilibrium of electronic correlations and how it might be manipulated. Here, we use synchrotron single-crystal x-ray diffraction, inelastic x-ray scattering, and lattice-dynamics calculations to clarify the origin of the CDW in EuAl4. We observe a broad softening of a transverse acoustic phonon mode that sets in well above room temperature and, at TCDW=142 K, freezes out in an atomic displacement mode described by the superspace group Immm(00γ)s00. In the context of previous work, our observation is a clear confirmation that the CDW in EuAl4 is driven by electron-phonon coupling. This result is relevant for a wider family of BaAl4 and ThCr2Si2-type rare-earth intermetallics known to combine CDW instabilities and complex magnetism. Published by the American Physical Society 2024

Synthesis, magnetic and superconducting properties of high-entropy rare-earth boride (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)(Rh,Ru)4B4

We report the structure and physical properties of a new rare-earth (RE) high-entropy boride (HEB) (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)(Rh0.85Ru0.15)4B4. The as-cast HEB consists of a highly crystallized, body-centered-tetragonal phase (I41/acd, a = 7.460 Å and c = 14.860 Å); here, all the RE elements share the same crystallographic site and are distributed uniformly on both macroscopic and microscopic scales. At high temperature, the HEB shows a paramagnetic behavior with a large effective moment peff yet it becomes a bulk superconductor upon cooling below 6.0 K. Remarkably, a peculiar cocktail effect of properties is observed: while the lattice parameters, Tc and peff of the HEB agree reasonably well with the compositional averages of the individual pseudo-ternary counterparts, the increased RE mixing entropy tends to suppress the superconductivity even without the magnetic exchange interactions, and a reentrant resistive transition is induced at magnetic fields above 0.8 T. Our results indicate that the high-entropy design of the RE sublattice is a viable way to tune the electrical and magnetic properties in RE intermetallics.

Metamagnetic multiband Hall effect in Ising antiferromagnet ErGa2

Frustrated rare-earth-based intermetallics provide a promising platform for emergent magnetotransport properties through exchange coupling between conduction electrons and localized rare-earth magnetic moments. Metamagnetism, the abrupt change of magnetization under an external magnetic field, is a signature of first-order magnetic phase transitions; recently, metamagnetic transitions in frustrated rare earth intermetallics have attracted interest for their accompanying nontrivial spin structures (e.g., skyrmions) and associated nonlinear and topological Hall effects (THE). Here, we present metamagnetism-induced Hall anomalies in single-crystalline ErGa2, which recalls features arising from the THE but wherein the strong Ising-type anisotropy of Er moments prohibits noncoplanar spin structures. We show that the observed anomalies are neither due to anomalous Hall effect nor THE; instead, can be accounted for via 4f-5d interactions which produce a band-dependent mobility modulation. This leads to a pronounced multiband Hall response across the magnetization process-a metamagnetic multiband Hall effect that resembles a topological-Hall-like response but without nontrivial origins. The present findings may be of general relevance in itinerant metamagnetic systems regardless of coplanar/noncoplanar nature of spins and are important for the accurate identification of Hall signals due to emergent magnetic fields.

Transition from an incommensurate spin density wave to a commensurate magnetic order in a triangular lattice compound Ho2PdAl6Ge4

Rare-earth (RE) intermetallics on a triangular lattice are promising candidates for generating interesting magnetic phases due to the complex interplay between Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction and geometrical frustration. Here we report the exotic magnetic structure of a layered compound Ho2PdAl6Ge4 with triangular lanthanide nets. Magnetization and heat capacity measurements in zero magnetic field reveal two magnetic phase transitions at TN1 = 10.8 K and TN2 = 6.0 K. Neutron powder diffraction demonstrates a commensurate antiferromagnetic phase with k1 = (0, 0, 1.5) below TN2. With increasing temperature, another incommensurate vector appears and therefore, the magnetic structure of the intermediate state is identified as an unusual incommensurate spin density wave with two propagation vectors k1 = (0, 0, 1.5) and k2 = (0.0492, 0.0492, 1.5). The magnetic moments in the intermediate state rotate continuously and form an unusual S-shaped wave arrangement in the ab plane, sharing similarities with typical cycloid and helix magnetic orders. These results identify Ho2PdAl6Ge4 as a candidate for exploring field-induced topological magnetic phases such as skyrmions, opening the way for further investigations on the family of RE2PdAl6Ge4 materials.

Effect of Hydrogenation on the Magnetic and Magnetocaloric Properties of Rare Earth Intermetallic Compounds Tb0.33Ho0.33Er0.33Ni and Dy0.33Ho0.33Er0.33Ni

Effect of Hydrogenation on the Magnetic and Magnetocaloric Properties of Rare Earth Intermetallic Compounds Tb0.33Ho0.33Er0.33Ni and Dy0.33Ho0.33Er0.33Ni

Magnetism in the axion insulator candidate Eu5In2Sb6

Eu5In2Sb6 is a member of a family of orthorhombic nonsymmorphic rare-earth intermetallics that combines large localized magnetic moments and itinerant exchange with a low carrier density and perpendicular glide planes. This may result in special topological crystalline (wallpaper fermion) or axion insulating phases. Recent studies of Eu5In2Sb6 single crystals have revealed colossal negative magnetoresistance and multiple magnetic phase transitions. Here, we clarify this ordering process using neutron scattering, resonant elastic x-ray scattering, muon spin-rotation, and magnetometry. The nonsymmorphic and multisite character of Eu5In2Sb6 results in coplanar noncollinear magnetic structures with an Ising-like net magnetization along the a axis. A reordering transition, attributable to competing ferro- and antiferromagnetic couplings, manifests as the onset of a second commensurate Fourier component. In the absence of spatially resolved probes, the experimental evidence for this low-temperature state can be interpreted either as an unusual double-q structure or in a phase separation scenario. The net magnetization produces variable anisotropic hysteretic effects which also couple to charge transport. The implied potential for functional domain physics and topological transport suggests that this structural family may be a promising platform to implement concepts of topological antiferromagnetic spintronics. Published by the American Physical Society 2024

A Study of Rare Earth Intermetallic Compound La0.73Dy0.27Mn2Si2 by Raman Spectroscopy, Magnetic Force Microscopy, and Resonance Photoemission Spectroscopy

A Study of Rare Earth Intermetallic Compound La0.73Dy0.27Mn2Si2 by Raman Spectroscopy, Magnetic Force Microscopy, and Resonance Photoemission Spectroscopy

Topological aspects of multi-k antiferromagnetism in cubic rare-earth compounds

We advertise rare-earth intermetallics with high-symmetry crystal structures and competing interactions as a possible materials platform hosting spin structures with non-trivial topological properties. Focusing on the series of cubic RCu compounds, where R = Ho, Er, Tm, the bulk properties of these systems display exceptionally rich magnetic phase diagrams hosting an abundance of different phase pockets characteristic of antiferromagnetic order in the presence of delicately balanced interactions. The electrical transport properties exhibit large anomalous contributions suggestive of topologically non-trivial winding in the electronic and magnetic structures. Neutron diffraction identifies spontaneous long-range magnetic order in terms of commensurate and incommensurate variations of (ππ0) antiferromagnetism with the possibility for various multi- k configurations. Motivated by general trends in these materials, we discuss the possible existence of topologically non-trivial winding in real and reciprocal space in the class of RCu compounds including antiferromagnetic skyrmion lattices. Putatively bringing together different limits of non-trivial topological winding in the same material, the combination of properties in RCu systems promises access to advanced functionalities.

Interpretable Machine Learning in Solid-State Chemistry, with Applications to Perovskites, Spinels, and Rare-Earth Intermetallics: Finding Descriptors Using Decision Trees

Interpretable Machine Learning in Solid-State Chemistry, with Applications to Perovskites, Spinels, and Rare-Earth Intermetallics: Finding Descriptors Using Decision Trees

Critical behavior in the itinerant ferromagnet SmMn2Ge2

Transition metal and rare earth intermetallics have been a fertile playground for research of various quantum states. We report detailed magnetic studies on SmMn2Ge2, an anisotropic itinerant magnet with multiple magnetic phases. The critical behavior of the ferromagnetic phase transition is investigated by employing the modified Arrott plot with the Kouvel–Fisher method. The critical temperature T C is determined to be around 342.7 K with critical exponents of β = 0.417 and γ = 1.122, and the interaction function is found to be J(r) ∼ r −4.68, suggesting the coexistence of long-range and short-range magnetic interactions. Our results contribute to the understanding of complex magnetism in SmMn2Ge2, which may provide fundamental guidance in future spintronic applications.

Effects of composition variation and hydrogenation on magnetocaloric properties of the (Gd1-xTbx)Ni (x = 0.1; 0.9) compounds

To identify promising magnetic refrigerant materials, we have studied the influence of composition variations and hydrogenation on the magnetocaloric effect (MCE) of the (Gd1-xTbx)Ni compounds. The end compositions of the series, Gd0.9Tb0.1Ni and Gd0.1Tb0.9Ni crystallize in orthorhombic CrB-type and monoclinic TbNi-type structures, respectively. Hydrogenation boosts the unit cell volume of (Gd,Tb)Ni by more than 20 % upon absorption of 4 at.H/f.u. Hydrogen absorption changes the structure type from TbNi to the CrB-type in Gd0.1Tb0.9Ni. Decrease of the Curie temperature in hydrides reaches ∼ 60 K. The magnetocaloric effect in (Gd,Tb)NiHy (y = 0 and 4) obtained by indirect method in the vicinity of TC revealed similar values of the maximum of specific isothermal entropy change -ΔST = 20.5 J kg−1 K−1 for Gd0.9Tb0.1Ni and its hydride Gd0.9Tb0.1NiH4 at μ0ΔH = 7 T. We show that the controlled synthesis of hydrides allows us to tailor the magnetocaloric effect in the multicomponent rare earth intermetallics and obtain materials with largely different TCs but with the same MCE values that are attractive for use in low-temperature magnetic cooling applications.

The Electronic and Thermodynamic Properties of Ternary Rare Earth Metal Alloys

This article uses the FP-LAPW approach within the DFT method, and the quasi-harmonic Debye model to investigate the electronic and thermodynamic properties of intermetallic rare earth materials (such as SmInZn, SmInCd, and SmTlZn). Thermodynamic properties were determined by the quasi-harmonic Debye model, whereas the FP-LAPW approaches within DFT method were utilized to derive electronic properties. The calculated structural parameters and the available experimental data have been examined, and it was observed that there was a good agreement between available experimental and calculated values of structural parameters. The electronic behavior of SmInZn, SmInCd and SmTlZn compounds shows the metallic character. We have examined a few thermodynamic characteristics. All calculated characteristics were found to match experimental or theoretical calculations.

Effect of oxidation on the microwave absorption properties of rare-earth intermetallics La2Fe4Co10B

Microwave absorbers are increasingly being used to enhance shielding performance at higher frequencies. Great effort has been made to develop materials with superior reflection loss (RL), thin thickness, wide bandwidth, and low density to improve their performance in electromagnetic microwave absorption. In this work, the rare-earth intermetallics La2Fe4Co10B fine powders with planar magnetocrystalline anisotropy and high magnetization were prepared using the hydrogenation desorption (HD) technique. By heating the obtained magnetic powders in the air to slowly form an oxide layer on their surfaces, its complex permittivity can be tuned without changing its complex permeability, and its microwave absorption performance can be dramatically enhanced due to the improved impedance matching condition. For the La2Fe4Co10B/paraffin composite, the real part of the complex permittivity at 10 GHz can be reduced from 20.1 to 12.8, decreasing 36.3%. Before the oxidation, the RL of La2Fe4Co10B/paraffin composite is only −14.8 dB at 3.3 GHz under 3.4 mm thickness with an effective absorption bandwidth (EAB) of 0.9 GHz. However, after the 10-hour oxidation, the RL changes to −15.6 dB at 13.4 GHz under 1.4 mm thickness with an EAB of 6.2 GHz. As an efficient and lightweight absorber, La2Fe4Co10B/paraffin composite has potential application value in constructing a new microwave absorber.

Revealing Hidden Patterns through Chemical Intuition and Interpretable Machine Learning: A Case Study of Binary Rare-Earth Intermetallics RX

Machine learning algorithms have been applied successfully in many areas of materials chemistry but often suffer from an inability to extract chemical insight. To demonstrate that an approach combining machine learning and chemical intuition can be effective in generating interpretable models, the structures of binary equiatomic rare-earth intermetallics RX, whose relationships have long defied understanding, were investigated as a case study. A structure map was developed based on only two parameters, which are derived from simple elemental descriptors (atomic number, period and group numbers, radii, and electronegativity) of the R and X components. This map reveals the previously hidden patterns of structural regularities of RX intermetallics. It explains the preference for CsCl-, TlI-, or FeB-type structures among these compounds, predicts the structures of missing members, rationalizes the occurrence of metastable phases and polymorphic transformations, and offers strategies for structure stabilization through the addition of a third component.

Long-Term in Vitro Corrosion of Biodegradable WE43 Magnesium Alloy in DMEM

The biodegradable WE43 magnesium alloy is an attractive biomedical material for orthopaedic implants due to its relatively high strength and corrosion resistance. Understanding the long-term corrosion behaviour in the human body plays a crucial role in the biomedical development and application of WE43 alloy for orthopaedic implants. In this work, the corrosion of an extruded WE43 magnesium alloy was investigated in a physiological environment using Dulbecco’s Modified Eagle Medium’s (DMEM) over a period of up to 10 weeks. To assess the in vitro corrosion process, we analysed the corrosion pits of the specimens’ cross sections and the composition of the corrosion layer by scanning electron microscopy. The experimental results indicated that the long-term corrosion process of WE43 magnesium alloy consists of three stages: (1) The rapid corrosion stage within the first 7 days, (2) the steady corrosion stage between 7 and 28 days, (3) the accelerated corrosion stage between 28 and 70 days. The microchemical analysis revealed a heterogeneous three-layer corrosion product with varying thicknesses of 10 to 130 µm on the surfaces of the samples for all corrosion times. It is composed of an inner layer of Mg-O, an intermediate layer of Mg-O-Ca-P, and an outer layer of Mg-O-Ca-P-C. The corrosion layers have many microcracks that allow limited contact between the liquid medium and the surface of the alloy. In addition, microgalvanic corrosion was observed to cause corrosion pits between the intermetallic rare earth element-rich phases and the Mg matrix.

Near-room temperature topological Hall effect at spin reorientations in sputtered NdCo5−xCux thin film

The spin reorientation in rare-earth intermetallics involves distinctive magnetic morphologies commencing with spontaneous skyrmion textures without an external magnetic field. Here, we present the sputtering growth of CaCu5-type NdCo5−xCux thin films on MgO (110) substrates. Our films exhibit two successive spin reorientation transitions between the ab-plane and the c-axis, close to the room temperature, apart from the non-uniaxial behavior below 150 K. The corresponding modulations of magnetocrystalline anisotropy at reorientation temperatures lead to the large topological Hall effect, which can be maintained up to 250 K with a maximum Hall resistivity of 210 nΩ cm. These results of robust topological signals will provide platforms for realizing room-temperature topological magnetic textures.

Thermodynamic and kinetic analysis of ternary intermetallics formation in Al–Cu–La alloy

The thermodynamic and kinetic analysis of rare earth (RE) intermetallics formation in Al–Cu–La alloy was carried out in this study. The formation enthalpy, excess entropy, excess Gibbs free-energy and activity of each component of Al–Cu–La ternary alloy were calculated combining Miedema model with Toop model. The calculated results show that the formation enthalpy, excess entropy and excess Gibbs free-energy of Al–Cu–La ternary alloy are all negative in the whole alloy composition range. The activities of Al, Cu and La are all tiny in the central zone of composition triangle of Al–Cu–La ternary alloy, indicating that Al, Cu and La components are easy to form ternary intermetallics. Moreover, the parabolic growth kinetics equation of RE intermetallics was derived integrating the Fick's second law with the mass balance law. According to the parabolic growth rate, the thickness of the RE intermetallics increases in proportion to the square root of the diffusion time.

High-field magnetization studies and their analysis in RFe11Ti and RFe11TiH1 rare-earth intermetallics (an example: HoFe11TiHx, x = 0 and 1)

We present experimental high-field magnetization studies for the single-crystalline ferrimagnetic RFe11Ti compounds at example of holmium-based hydride in order to evaluate, compare and analyze the crystal-field and exchange parameters. We predict theoretically the magnetization behavior of HoFe11Ti up to 80 T magnetic field for the first time. The results are compared with data for the parent compound HoFe11TiH1 and those with erbium and thulium (x = 0 and 1).

Machine-learning enabled thermodynamic model for the design of new rare-earth compounds

We employ a descriptor based machine-learning approach to assess the effect of chemical alloying on formation-enthalpy of rare-earth intermetallics. Application of machine-learning approaches in rare-earth intermetallic design have been sparse due to limited availability of reliable datasets. In this work, we developed an ‘in-house’ rare-earth database with more than 600 + compounds, each entry was populated with formation enthalpy and related atomic features using high-throughput density-functional theory (DFT). The SISSO (sure independence screening and sparsifying operator) based machine-learning method with meaningful atomic features was used for training and testing the formation enthalpies of rare earth compounds. The complex lattice function coupled with the machine-learning model was used to explore the effect of transition metal alloying on the energy stability of Ce based cubic Laves phases (MgCu2 type). The SISSO predictions show good agreement with high-fidelity DFT calculations and X-ray powder diffraction measurements. Our study provides quantitative guidance for compositional considerations within a machine-learning model and discovering new metastable materials. The electronic-structure of Ce-Fe-Cu based compound was also analyzed to get an in-depth understanding of the electronic origin of phase stability. The interpretable analytical models in combination with density-functional theory and experiments provide a fast and reliable design guide for discovering technologically useful materials.

Low temperature deformation mechanisms of polycrystalline CoZr and Co39Ni11Zr50 B2-type intermetallic compounds

The B2-type intermetallic compounds CoZr and Co39Ni11Zr50 were deformed in tension at low temperatures. While CoZr is ductile down to 4 K, Co39Ni11Zr50 becomes brittle below 125 K due to a martensitic phase transformation. Thermal activation analysis shows that CoZr follows the Cottrell-Stokes law indicating forest dislocation cutting as the dominant rate-controlling deformation mechanism, similar to face-centered cubic metals. The moderate ductility of both intermetallic compounds at low temperatures may qualitatively be related to a significant metallic character of bonding giving rise to a low Peierls stress estimated for primary {110}<100> slip and most likely also leads to an easier activation of secondary {110}<110> slip which was proven by transmission electron microscopy. Secondary slip is necessary for the fulfillment of the von Mises criterion for homogeneous plastic deformation of polycrystalline materials. The present results generalize the findings made on the ductile rare earth intermetallics YAg and YCu and, therefore, may help to search for other ductile systems in the broad class of intermetallic compounds.