C14 Nb(Fe89.4Al10.6)2 Laves phase intermetallic compound was investigated by DC magnetization (M) measurements performed in the temperature (T) interval of 20 to 175 K,under an applied magnetic field (H) ranging between 50 and 1250 Oe. Magnetization curves were recorded in the field-cooled (FC) and in the zero-field-cooled (ZFC) modes. They clearly showed an irreversible character that vanished at H=1250 Oe. Both magnetization curves exhibited well-defined peaks around T_N =72.3 K whose positions were H-independent, so they were identified as the compound's Néel temperature. The existence of irreversibility which decreases with H testify to a re-entrant character of magnetism in the studied compound. An increase of both MFC and MZFC observed below TN likely indicates a mixed i.e. ferromagnetic and antiferromagnetic ground magnetic state of the studied system.
Based on density functional calculations, the relationship between magnetism or superconductivity and electronic states around Fermi level were derived, and the location of the Fermi level in nonmagnetic "form" of Laves-phase compounds is very sensitive to determine the presence of nonmagnetism, or ferromagnetism, or antiferromagnetism, or superconductivity. The Fermi level at the nonbonding and antibonding regions corresponds for the nonmagnetism and magnetism, respectively, whereas at bonding region with responsibility for superconductivity. This rules will be very useful and convenient to s…
Strain heterogeneity at the microstructural level plays a vital role in the deformation and fracture behaviour of dual or multi-phase materials. In the present work, the strain heterogeneity, localization and partitioning arising at the sub-micron scale during elevated temperature (170 °C) tensile deformation of an Mg-5Al-3Ca alloy was investigated using quasi in-situ μ-DIC experiments. The results reveal that the strain is mainly carried by the α-Mg phase, while the intermetallic Laves phase plays a critical role in that strain concentrations build up at the α-Mg matrix and Laves phase interf…
Laves RFe2 compounds, where R is a rare earth, exhibit technologically relevant properties associated with the interplay between their lattice geometry and magnetism. We apply ab~initio calculations to explore how magnetic properties of Fe in RFe2 systems vary with temperature. We found that the ratio between the orbital magnetic moment m_orb and the spin magnetic moment m_spin increases with increasing temperature for YFe2, GdFe2, TbFe2, DyFe2, and HoFe2. This increase is significant and it should be experimentally observable by means of x-ray magnetic circular dichroism. We conjecture that t…
Here we perform $ab-initio$ study of Curie temperature $T_C$ under hydrostatic pressure for intermetallic compound GdFe$_2$. To calculate $T_C$ for GdFe$_2$ we applied mean-field solution of the Heisenberg model for several magnetic sublattices with DFT/LDA calculated values of necessary exchange interaction integrals and local magnetic moments. To compare with available experimental data pressure values were taken from zero up to about 70 Kbar. It corresponds to 2\% compression of the volume of the unit cell. In agreement with experimental data $T_C$ grows under pressure. It was shown that Fe…
The microstructure of Mg-Al-Ca alloys consists of a hard intra- and intergranular eutectic Laves phase network embedded in a soft $α$-Mg matrix. For such heterogeneous microstructures, the mechanical response and co-deformation of both phases under external load are not yet fully understood. We therefore used nano- and microindentation in combination with electron microscopy to study the deformation behaviour of an Mg-3.68Al-3.8Ca alloy. We found that the hardness of the Mg$_2$Ca phase was significantly larger than the $α$-Mg phase and stays constant within the measured temperature range. The …
A new Laves phase superconductor NbBe2, prototype with MgCu2, having maximum Tc ~2.6 K has been reported very recently. Based on first-principle calculations, we systematically study the structural, elastic, mechanical, electronic, thermal and superconducting properties of the newly reported superconducting intermetallic compound NbBe2. Finally, we investigate the electron-phonon coupling constant, phonon dispersion curve and density of states which indicates that the compound under study is a weakly coupled BCS superconductor.
Structural, elastic, electronic and optical properties of laves phase intermetallic compounds CaRh2 and LaRh2 prototype with MgCu2 are investigated by using the first principle calculations. These calculations stand on density functional theory (DFT) from CASTEP code. The calculated lattice parameters are consistent with the experimental values. The significant elastic properties, like as bulk modulus, shear modulus, Youngs modulus and the Poissons ratio are determined by applying the Voigt Reuss Hill (VRH) approximation. The analysis of Pughs ratio shows the ductile nature of both the phases.…
We study a cast Mg-4.65Al-2.82Ca alloy with a microstructure containing $α$-Mg matrix reinforced with a C36 Laves phase skeleton. Such ternary alloys are targeted for elevated temperature applications in automotive engines since they possess excellent creep properties. However, in application, the alloy may be subjected to a wide range of strain rates and in material development, accelerated testing is often of essence. It is therefore crucial to understand the effect of such rate variations. Here, we focus on their impact on damage formation. Due to the locally highly variable skeleton formin…
Two different mechanisms have been reported in previous ab initio studies to describe basal slip in complex intermetallic Laves phases: synchroshear and undulating slip. To date, no clear answer has been given on which is the energetically favourable mechanism and whether either of them could effectively propagate as a dislocation. Using classical atomistic simulations supported by ab initio calculations, the present work removes the ambiguity and shows that the two mechanisms are, in fact, identical. Furthermore, we establish synchroshear as the mechanism for propagating dislocations within t…
Crystal-field (CF) effects on the rare-earth (RE) ions in ferrimagnetic intermetallics NdCo$_5$ and TbCo$_5$ are evaluated using an ab initio density functional + dynamical mean-field theory approach in conjunction with a quasi-atomic approximation for on-site electronic correlations on the localized 4$f$ shell. The study reveals an important role of the high-order sectoral harmonic component of the CF in the magnetism of RECo$_5$ intermetallics. An unexpectedly large value is computed in the both systems for the corresponding crystal-field parameter (CFP) $A_6^6 \langle r^6 \rangle$, far beyo…
Activation of non-basal slip is essential in improving the deformability of hexagonal crystals. However, the mechanism of non-basal slip remains largely unknown, especially for complex intermetallics such as Laves phases. In this work, the prismatic slip systems of C14 Laves crystals and possible metastable states along the slip paths are assessed using atomistic simulations. Multiple prismatic stacking fault states with the same lattice pattern but different site occupancies and chemical distributions are identified at different inter-atomic layers, temperatures and chemical compositions. The…
The quantum critical point (QCP) in the archetypical heavy-fermion compound CeCu$_6$ doped by Au is described, accounting for the localized $4f$-electron of Ce, using realistic electronic structure calculations combined with dynamical mean-field theory (DMFT). Magnetism trends in Ce(Cu$_{1-ε}$Au$_ε$)$_6$ are compared with those in Co-doped CeCu$_{5}$, which resides on the non-ferromagnetic side of the composition space of one of the earliest rare-earth permanent magnet compounds, Ce(Co,Cu)$_5$. The construction of a realistic Doniach phase diagram shows that the system crosses over a magnetic …
We report temperature dependent ac susceptibility ($χ$) measurements on a high quality single crystal of Tb$_2$PdSi$_3$, crystallizing in a AlB$_2$-derived hexagonal structure. This compound is found to exhibit features attributable to quasi-low-dimensional magnetism at high temperatures and {\it anisotropic} spin-glass-like behavior at low temperatures ($<$ 10 K) with an unusually large frequency dependence of peak temperature in ac $χ$(T). This compound thus presents a novel situation in {\it metallic magnetism}, considering that the former phenomenon is normally encountered only among insul…
The mechanical behaviour of Mg-Al alloys can be largely improved by the formation of an intermetallic Laves phase skeleton, in particular the creep strength. Recent nanomechanical studies revealed plasticity by dislocation glide in the (Mg,Al)$_2$Ca Laves phase, even at room temperature. As strengthening skeleton, this phase remains, however, brittle at low temperature. In this work, we present experimental evidence of slip transfer from the Mg matrix to the (Mg,Al)$_2$Ca skeleton at room temperature and explore associated mechanisms by means of atomistic simulations. We identify two possible …
Intermetallic phases can significantly improve the creep resistance of magnesium alloys, extending their use to higher temperatures. However, little is known about the deformation behaviour of these phases at application temperatures, which are commonly below their macroscopic brittle-to-ductile-transition temperature. In this study, we therefore investigate the activation of different slip systems of the CaMg$_2$ phase and the occurrence of serrated yielding in the temperature range from 50$^\circ$C to 250$^\circ$C. A decreasing amount of serrated flow with increasing temperature suggests tha…
We explain a profound complexity of magnetic interactions of some technologically relevant gadolinium intermetallics using an ab-initio electronic structure theory which includes disordered local moments and strong $f$-electron correlations. The theory correctly finds GdZn and GdCd to be simple ferromagnets and predicts a remarkably large increase of Curie temperature with pressure of +1.5 K kbar$^{-1}$ for GdCd confirmed by our experimental measurements of +1.6 K kbar$^{-1}$. Moreover we find the origin of a ferromagnetic-antiferromagnetic competition in GdMg manifested by non-collinear, cant…
In this present investigation, we discussed the synthesis, microstructure, and hydrogen storage behavior intermetallic Laves phase in a hexanal TiVZrMnCoFe high entropy alloy. In this HEA, three elements are hydride-forming elements and the other three are non-hydride-forming elements (Fe, Mn, Co). The thermodynamic parameter like enthalpy of mixing was calculated using Meidmas model.The possibility of developing high entropy Laves phase-based hydrogen storage materials was advocated.
This work has been presented by RJCV to obtain his PhD degree at Fluminense Federal University, in March of 2017. We focused on the synthesis of compounds and then on their magneto-strucutral characterization; mainly due to the interplay of these physical properties. We have prepared intermetallic alloys (including Heusler alloys) and perovskite oxides (manganites and cobaltites); in bulk and nanoparticles. A thorough analysis of the influence of the morphology and crystal structure on the magnetic properties of these compounds is addressed.
Metallic Bonding-Driven Elastic Softness and Optical Response in the Mg-Rich Laves-Phase LaMg2
Pabna Textile Engineering College, Bangladesh University of Textiles（帕尔纳纺织工程学院，孟加拉国纺织大学）；EcoBengal Centre for Materials and Energy Research（生态孟加拉材料与能源研究中心）；Bangladesh Atomic Energy Regulatory Authority (BAERA)（孟加拉国原子能监管局）；Department of Physics, University of Barishal（巴里萨尔大学物理系）；Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology（名古屋工业大学电气与机械工程系）；School of Materials Science and Engineering, Faculty of Science, University of New South Wales（新南威尔士大学理学院材料科学与工程系）
Zonal dislocations in Laves phases: A coupled synchro-shear slip mechanism
RWTH Aachen University（亚琛工业大学）；Ruhr University Bochum（波鸿鲁尔大学）；Max Planck Institute for Sustainable Materials（马普可持续材料研究所）；Fuyao University of Science and Technology（福耀科技大学）；Université de Lorraine（洛林大学）；Helmholtz-Zentrum Berlin für Materialien und Energie（柏林亥姆霍兹材料与能源中心）
By virtue of the itinerant electron metamagnetism (IEM), the RCo2 compounds with R=Er, Ho and Dy are found to show first order magnetic transition at their ordering temperatures. The inherent instability of Co sublattice magnetism is responsible for the occurrence of IEM, which leads to interesting magnetic and related properties. The systematic studies of the variations in the magnetic and magnetocaloric properties of the RCo2-based compounds show that the magnetovolume effect plays a decisive role in determining the nature of magnetic transitions and hence the magnetocaloric effect (MCE) in …
A new ternary intermetallic compound, namely, YbMn2Sb2, has been synthesized and its magnetic and electrical transport properties have been studied in the temperature range of 2 to 300 K. This compound crystallizes in a trigonal, La2O2S type structure (space group P3bm1, No. 164) and is found to be ferromagnetically ordered at room temperature. The magnetism is attributed to the ordering of Mn sublattice. M5 xray absorption spectrum of YbMn2Sb2 obtained at room temperature suggests that the valency of Yb in this compound is close to 2. Electrical resistivity of this compound is metal like and …
Sigma-phase intermetallic compound of Fe54Cr46 was investigated using DC and AC magnetic susceptibility techniques. A clear-cut evidence was found that the sample orders magnetically at Tc=23.5 K and its ground magnetic state is constituted by a spin glass. The temperature at which the zero-field cooled magnetization has its maximum decreases with an external magnetic field in line with the Gabay-Toulouse prediction. The temperature at which the AC magnetic susceptibility has its maximum does not depend on frequency which, in the light of the mean-field theory, testifies to very long magnetic …
Magnetism of the binary intermetallic compound MnGa$_4$ is re-investigated. Band-structure calculations predict antiferromagnetic behavior in contrast to Pauli paramagnetism reported previously. Magnetic susceptibility measurements on single crystals indeed reveal an antiferromagnetic transition at $T_N=393$ K. Neutron powder diffraction and $^{69,71}$Ga nuclear quadrupole resonance spectroscopy show collinear antiferromagnetic order with magnetic moments alligned along the [111] direction of the cubic unit cell. The magnetic moment of 0.80(3)$μ_B$ at 1.5 K extracted from the neutron data is i…
Computational design of more efficient rare earth/transition metal (RE-TM) permanent magnets requires accurately calculating the magnetocrystalline anisotropy (MCA) at finite temperature, since this property places an upper bound on the coercivity. Here, we present a first-principles methodology to calculate the MCA of RE-TM magnets which fully accounts for the effects of temperature on the underlying electrons. The itinerant electron TM magnetism is described within the disordered local moment picture, and the localized RE-4f magnetism is described within crystal field theory. We use our mode…
We are witnessing a great transition towards a society powered by renewable energies to meet the ever-stringent climate target. Hydrogen, as an energy carrier, will play a key role in building a climate-neutral society. Although liquid hydrogen is essential for hydrogen storage and transportation, liquefying hydrogen is costly with the conventional methods based on Joule-Thomas effect. As an emerging technology which is potentially more efficient, magnetocaloric hydrogen liquefaction is a "game-changer". In this work, we have investigated the rare-earth-based Laves phases ${\rm R}Al_2$ and ${\…
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors of $Q_{\pm}$ = ($H \pm 0.557(1)$, 0, $L \pm 0.150(1)$) a…
Magnetic properties of the intermetallic compound NdCo$_2$Si$_2$ are investigated by using the Monte Carlo simulation (MCs) under Metropolis algorithm. The magnetism of the compound is caused by the existence of the rare earth (Nd3+) ions with a magnetic moment taking the value 2.7 muB. Firstly, the ground state phase diagrams are presented and discussed in different planes corresponding to different physical parameters of the system. The stable phases are explored for different configurations of the Hamiltonian of the system. These stable phases are determined by the minimal energies. For non…
Surface alloying is a straightforward route to control and modify the structure and electronic properties of surfaces. Here, We present a systematical study on the structural and electronic properties of three novel rare earth-based intermetallic compounds, namely ReAu2 (Re = Tb, Ho, and Er), on Au(111) via directly depositing rare-earth metals onto the hot Au(111) surface. Scanning tunneling microscopy/spectroscopy measurements reveal the very similar atomic structures and electronic properties, e.g. electronic states, and surface work functions, for all these intermetallic compound systems d…
Among the members of the series R2PdSi3 (R= Rare-earths), the magnetic behavior of the Nd compound is interesting in some respects. This compound is considered to order ferromagnetically (below 16 K), unlike other members of this series which order antiferromagnetically. In addition, magnetic ordering temperature (To) is significantly enhanced with respect to de Gennes scaled value. In order to understand the magnetism of this compound better, we have investigated the magnetic behavior in detail (under external pressure as well) and also of its solid solutions based on substitutions at Nd and …
The magnetic properties of the intermetallic compound FeAl are investigated using exact exchange density functional theory. This is implemented within a state of the art all-electron full potential method. We find that FeAl is magnetic with a moment of 0.70 $μ_B$, close to the LSDA result of 0.69 $μ_B$. A comparison with the non-magnetic density of states with experimental negative binding energy result shows a much better agreement than any previous calculations. We attribute this to the fine details of the exchange field, in particular its asymmetry, which is captured very well with the orbi…
The synthesis of materials in high-pressure experiments has recently attracted increasing attention, especially since the discovery of record breaking superconducting temperatures in the sulfur-hydrogen and other hydrogen-rich systems. Commonly, the initial precursor in a high pressure experiment contains constituent elements that are known to form compounds at ambient conditions, however the discovery of high-pressure phases in systems immiscible under ambient conditions poses an additional materials design challenge. We performed an extensive multi component $ab\,initio$ structural search in…
Recent experiments on Pd$_{3}$Fe intermetallics [Phys. Rev. Lett. 102, 237202 (2009)] have revealed that the system behaves like a classical invar alloy under high pressure. The experimental pressure-volume relation suggests an anomalous volume collapse and a substantial increase in bulk modulus around the pressure where invar behavior is observed. With the help of first-principles density functional theory based calculations, we have explored various magnetic phases (ferromagnetic, fully and partially disordered local moment, spin spiral) in order to understand the effect of pressure on magne…
The intermetallic compound \PFA\ that possesses a three-dimensional network structure of Al polyhedra centered at the transition metal element Fe and the rare earth Pr is investigated through neutron powder diffraction and inelastic neutron scattering in order to elucidate the magnetic ground state of Pr and Fe and the crystal field effects of Pr. Our neutron diffraction study confirms long-range magnetic order of Pr below $T_N $ = 4.5~K in this compound. Subsequent magnetic structure estimation reveals a magnetic propagation vector $k$ = ($\frac{1}{2}$~0~$\frac{1}{2}$) with a magnetic moment …
Ab initio calculation results for the electronic structure of disordered bcc Fe(x)Al(1-x) (0.4<x<0.75), Co(x)Al(1-x) and Ni(x)Al(1-x) (x=0.4; 0.5; 0.6) alloys near the 1:1 stoichiometry, as well as of the ordered B2 (FeAl, CoAl, NiAl) phases with point defects are presented. The calculations were performed using the coherent potential approximation within the Korringa-Kohn-Rostoker method (KKR-CPA) for the disordered case and the tight-binding linear muffin-tin orbital (TB-LMTO) method for the intermetallic compounds. We studied in particular the onset of magnetism in Fe-Al and Co-Al systems a…
The close-packed AB$_2$ structures called Laves phases constitute the largest group of intermetallic compounds. In this paper we computationally investigated the pseudo-binary Laves phase system Y$_{1-x}$Gd$_x$(Fe$_{1-y}$Co$_y$)$_2$ spanning between the YFe$_2$, YCo$_2$, GdFe$_2$, and GdCo$_2$ vertices. While the vast majority of the Y$_{1-x}$Gd$_x$(Fe$_{1-y}$Co$_y$)$_2$ phase diagram is the ferrimagnetic phase, YCo$_2$ along with a narrow range of concentrations around it is the paramagnetic phase. We presented results obtained by Monte Carlo simulations of the Heisenberg model with parameter…
We have synthesized single crystals of CeZnAl$_3$, which is a new member of the family of the Ce-based intermetallics Ce$TX_3$ ($T$ = transition metal, $X$= Si, Ge, Al), crystallizing in the non-centrosymmetric tetragonal BaNiSn$_3$-type structure. Magnetization, specific heat and resistivity measurements all show that CeZnAl$_3$ orders magnetically below around 4.4 K. Furthermore, magnetization measurements exhibit a hysteresis loop at low temperatures and fields, indicating the presence of a ferromagnetic component in the magnetic state. This points to a different nature of the magnetism in …
Results are reported for the $f$-electron intermetallic CeAuAl$_4$Ge$_2$, where the atomic arrangement of the cerium ions creates the conditions for geometric frustration. Despite this, magnetic susceptibility measurements reveal that the low temperature magnetic exchange interaction is weak, resulting in marginally frustrated behavior and ordering near $T_{\rm{M}}$ $\approx$ 1.4 K. This occurs within a metallic Kondo lattice, where electrical resistivity and heat capacity measurements show that the Kondo-driven electronic correlations are negligible. Quantum oscillations are detected in ac-ma…
We investigate the effects of magnetic inhomogeneities and thermal fluctuations on the magnetic properties of a rare earth intermetallic compound, Nd$_2$Fe$_{14}$B. The constrained Monte Carlo method is applied to a Nd$_2$Fe$_{14}$B bulk system to realize the experimentally observed spin reorientation and magnetic anisotropy constants $K^{\rm A}_m (m=1, 2, 4)$ at finite temperatures. % Subsequently, it is found that the temperature dependence of $K^{\rm A}_1$ deviates from the Callen--Callen law, $K^{\rm A}_1(T) \propto M(T)^3$, even above room temperature, $T_{\rm R}\sim 300\rm\, K$, when the…
We report our comprehensive study of physical properties of a ternary intermetallic compound PrIrSi3 investigated by dc magnetic susceptibility chi(T), isothermal magnetization M(H), thermo-remnant magnetization M(t), ac magnetic susceptibility chi_ac(T), specific heat C_p(T), electrical resistivity rho(T), muon spin relaxation (muSR) and inelastic neutron scattering (INS) measurements. A magnetic phase transition is marked by a sharp anomaly at T_tr = 12.2 K in chi(T) measured at low applied fields which is also reflected in the C_p(T) data through a weak anomaly at 12 K. An irreversibility b…
