Showing papers on "Laves phase published in 1987"
TL;DR: On the basis of thermal expansion and NMR measurements, the stability of Mn moments and spin fluctuations in RMn2 are discussed in this paper, where it is shown that the interatomic distance plays a crucial role in determining the Mn magnetism.
78 citations
TL;DR: In this paper, the structural changes of the CeFe2 Laves phase compound during the hydrogen absorption and desorption process have been investigated by X-ray diffraction, transmission electron microscopy, thermal analysis and magnetic property measurements.
74 citations
TL;DR: In this paper, the properties of stoichiometric and off-stoichiometric NbFe 2 intermetallic compounds have been studied and it has been revealed that the stoico-nbFe2 shows strongly enhanced Pauli paramagnetic properties.
Abstract: Magnetic properties of stoichiometric and off-stoichiometric NbFe 2 intermetallic compounds have been studied. It has been revealed that the stoichiometric NbFe 2 shows strongly enhanced Pauli paramagnetic properties. The temperature dependence of its susceptibility in a weak external field shows a maximum as observed in other exchange enhanced metals such as TiBe 2 . The concentration deviations from the stoichiometry toward both sides result in ferromagnetism. The origins of the ferromagnetism in off-stoichiometric compositions are discussed.
51 citations
TL;DR: In this article, the thermal expansion and magnetic susceptibility have been measured for Y(Mn 1-xAlx)2 pseudobinary Laves phase intermetallic compounds and the amplitude of local spin fluctuations at the Mn site has been estimated on the basis of the phenomenological theory of magnetovolume effects.
Abstract: The thermal expansion and magnetic susceptibility have been measured for Y(Mn1-xAlx)2 pseudobinary Laves phase intermetallic compounds. A large volume change at TN and a remarkable enhancement of the thermal expansion coefficient above TN were observed in YMn2. The substitution of Al for Mn makes these anomalies less clear. The temperature dependence of the susceptibility, being almost temperature independent for YMn2, becomes of the Curie-Weiss type as the Al content increases. Such behaviour is explained as the characteristic features of spin fluctuations. The amplitude of local spin fluctuations at the Mn site has been estimated on the basis of the phenomenological theory of magnetovolume effects. It has been revealed that the magnetic ground state of Al-substituted compounds is a spin glass.
45 citations
TL;DR: In this paper, the effect of hydrogen capacity on crystallographic and magnetic properties has been studied on the Laves phase intermetallic of the C15 cubic YMn2 and the C14 hexagonal ZrMn 2.
Abstract: The effect of hydrogen capacity on crystallographic and magnetic properties has been studied on the Laves phase intermetallic of the C15 cubic YMn2 and the C14 hexagonal ZrMn2. It has been found that there exist intermediate metastable β′ phases between the α phase and the fully charged β phase in both compounds. The β′ phase has the same crystal structure as in the hydrogen-free compound and the unit cell volume is smaller than that in the β phase. Magnetization measurements indicate that the β′ phase stabilizes ferromagnetism and, in the β phase, antiferromagnetism or paramagnetism becomes stable. The results obtained are discussed on the assumption that there is a preferential site among the three kinds of tetrahedral hydrogen sites. ZrMn2 exhibited excellent hydrogen absorption properties for use in thermal energy conversion systems operating under high temperatures.
44 citations
TL;DR: In this article, the electronic structures of Laves phase compounds AB2 (A = Y, Zr, Nb; B = Cr, Mn, Co, Ni) were investigated systematically by the LMTO method within the framework of the LSD approximation.
38 citations
TL;DR: Magnetization measurements have been carried out on the Laves phase compounds M(Co 1− x Al x ) 2 (M = Y, Lu) up to 42 T as discussed by the authors.
35 citations
TL;DR: In this article, the influence of hydrogenation on the structural change and magnetic properties of the Laves-phase GdFe2 compound has been investigated, showing that hydrogenation sharply reduces the Curie temperature of the crystalline alloy from 818 to 107 K, in contrast to the hydrogen-induced amorphous alloy.
Abstract: The influence of hydrogenation on the structural change and magnetic properties of the Laves‐phase GdFe2 compound has been investigated. Crystalline c‐GdFe2 absorbs 4.4 hydrogen atoms per formula unit without any change in the crystal structure below 423 K. On the other hand, GdFe2 transforms to amorphous a‐GdFe2H3.6 by hydrogenation from 423 to 523 K, where the decomposition of GdFe2 into GdH2 and α‐Fe is prevented. The same amount of hydrogen (3.6 atoms per formula unit) dissolves in amorphous alloys produced by both hydrogenation and rapid quenching. Hydrogenation sharply reduces the Curie temperature of the crystalline alloy from 818 to 107 K, in contrast to the Curie temperature of 443 K for the hydrogen‐induced amorphous alloy. The temperature dependence of the magnetization of the hydrogen‐induced amorphous alloy is identical to that of the hydrogenated rapidly quenched amorphous alloy, suggesting similarity of their structures. The magnetization of the hydrogen‐induced amorphous alloy shows a broa...
34 citations
TL;DR: In this article, the CEF contributions in ErMn2 were observed and calculated using a single-ion Hamiltonian, showing that the Mn moment has an itinerant character and an additional CM is observable even above TN.
32 citations
TL;DR: In this paper, the temperature variation of the mean square local amplitude of spin fluctuation is essentially important for understanding magnetic properties of Laves phase compounds, MFe 2, for various M atoms.
31 citations
TL;DR: The structure of Y2Rh3Ge has been determined and refined from single-crystal X-ray diffraction data (R = 0.042) as mentioned in this paper, which is a rhombohedral, ternary ordered variant of the cubic Laves structure type MgCu2, with space group R 3 m, Z = 3, a = 5.552(3) and c = 11.82(1)A for the triple hexagonal cell.
TL;DR: A large number of samples of the general composition Zr1−xAlxT2, Zr 1−xSixT2 and Zr TixT2 (T ≡ Mn, Fe, Co) were prepared and investigated using X-ray diffractometry and metallography.
Abstract: A large number of samples of the general composition Zr1−xAlxT2, Zr1−xSixT2 and Zr1−xTixT2 (T ≡ Mn, Fe, Co) were prepared and investigated using X-ray diffractometry and metallography. It was found that in binary Friauf-Laves phases, ZrT2, zirconium can be replaced by aluminium or silicon up to the compositions Zr0.7A10.3Mn2, Zr0.7Si0.3Mn2, Zr0.6Al0.4Fe2, Zr0.5Si0.5Fe2, Zr0.4Al0.6Co2 and Zr0.6Si0.4Co2. In all these systems the crystal structure of the prototype compounds (the cubic MgCu2 or the hexagonal MgZn2 type) is preserved. In the Zr1−xTixT2 systems, continuous solid solutions were formed throughout the investigated region and their crystal structures depend on the composition and/or heat treatment. An ordering phenomenon was observed only in the Zr1−xALxCo2 system, where a superstructure of the MgSnCu4 type was formed at the composition Zr0.5A10.5Co2. The stability of these phases is briefly discussed in terms of the relative atomic sizes.
TL;DR: In this article, the transport coefficients and sum rules (Matthiessen rule, Kohler rule) are deduced in the framework of the linearized Boltzmann equation and the different contributions due to various scattering processes are calculated using transport spectral functions.
TL;DR: Amorphous Fel−xTix alloys with x = 0.2-0.75 have been investigated by differential scanning calorimetry, differential thermal analysis, X-ray diffraction and Mossbauer effect measurements.
TL;DR: In this paper, the metamagnetic transition between a paramagnetic and a ferromagnetic state which is the same as that of x = 0.12 and 0.17 was investigated.
Abstract: Magnetization measurements have been carried out for cubic Laves phase compounds Lu(Co 1- x Al x ) 2 . Stable ferromagnets at 4.2 K are found at the compositions of x =0.12 and 0.17, where the maximum moment and Curie temperature are 0.65 µ B per Co atom and 147 K, respectively. Anomalous magnetization curves with large hysteresis are found at x =0.08. This is understood by considering the metamagnetic transition between a paramagnetic and a ferromagnetic state which is the same as that of x =0.12. The transition is 1st order at temperatures below ∼65 K and is 2nd order above 65 K. It is found that a weak itinerant ferromagnetism, like that found in Y(Co 1- x Al x ) 2 and Sc(Co 1- x Al x ) 2 , is not clearly observed in this compound series.
TL;DR: In this article, the effect of randomization of the crystal field interaction in destroying long range order is illustrated in amorphous rare earth compounds and in rare earth compound hydrides.
TL;DR: The cubic Laves phase compound Ce(Fe 0.95 Al 0.05 ) 2 exhibits a first order magnetic phase transition from antiferromagnetic to ferromagnetic state at ≈ 100 K with increasing temperature as mentioned in this paper.
TL;DR: In this article, the large anistropic thermal expansions effects minimize the frustration of the Mn-Mn interactions, which is the case on ThMn2, where one Mn atom (2a) in four remains nonmagnetic whilst the others order in a triangular configuration.
TL;DR: In this paper, the electronic structure of d electrons in the cubic Laves phase of the intermetallic compounds ScCo2 and LuCo2 under an external magnetic field is calculated in the tight-binding approximation and in the Hartree-Fock approximation.
Abstract: The electronic structure of d electrons in the cubic Laves phase of the intermetallic compounds ScCo2 and LuCo2 under an external magnetic field is calculated in the tight-binding approximation and in the Hartree-Fock approximation The field dependence of the induced moment is obtained at 0K It is shown that the metamagnetic transition from the paramagnetic to the ferromagnetic state can occur at about 120 and 94 T for ScCo2 and LuCo2, respectively
TL;DR: In this paper, the hyperfine fields were calculated by the LMTO method in the framework of the LSD approximation for YMn 2 and the contribution from the valence electrons to hyperfine field is positive and anomalously large.
TL;DR: In this paper, heat-to-heat variability in corrosion resistance and microstructure that might be encountered in low carbon AISI 316 nuclear grade stainless steels (SSs) was considered.
Abstract: This paper considers the heat-to-heat variability in corrosion resistance and microstructure that might be encountered in low carbon AISI 316 nuclear grade stainless steels (SSs). The results will show that although these low carbon steels are rather resistant to sensltization by chromium depletion, they vary significantly in their grain size, inclusion content, and microstructural homogeneity. Aging for as long as 1000 h at 550 C did not produce grain boundary precipitation in any of these alloys; aging for 100 h at 650 C produced Laves phase along the grain boundaries of two alloys and chromium-rich M23C6 carbides in the other. Impurity segregation was low in all three alloys. The two alloys that contained Laves phase along their grain boundaries exhibited very little corrosion in the modified Strauss test. The other heat showed only slightly more corrosion because of very limited carbide precipitation. All of the alloys underwent corrosion in the more oxidizing Huey test. The amount of corrosi...
TL;DR: In this paper, the electronic structure of d electrons in the antiferromagnetic intermetallic compound YMn2 with the cubic Laves phase structure is calculated in the tight-binding approximation in the Hartree-Fock approximation.
Abstract: The electronic structure of d electrons in the antiferromagnetic intermetallic compound YMn2 with the cubic Laves phase structure is calculated in the tight-binding approximation In the Hartree-Fock approximation, the density of states curve and the sublattice moment of Mn atoms are calculated numerically at 0 K It is shown that the magnitude of the sublattice Mn moment decreases with decreasing lattice constant Furthermore, the parallel and perpendicular spin susceptibilities are calculated numerically at 0 K and it is shown that the perpendicular spin susceptibility is much larger than the parallel one A discussion on the magnetic structure of GdMn2 is given
TL;DR: In this paper, the nuclear magnetic resonance of 59 Co has been studied for cubic Laves phase compounds Lu(Co 1- x Al x ) 2 at a temperature of 4.2 K.
Abstract: Nuclear magnetic resonance of 59 Co has been studied for cubic Laves phase compounds Lu(Co 1- x Al x ) 2 at a temperature of 4.2 K. Coexistence of both the non-magnetic and the magnetic states of cobalt atoms was found in the sample with, x =0.08. Transitions in Co atoms from the nonmagnetic to the magnetic state were induced by magnetic field, which led to an anormalous magnetization curve with hysteresis.
TL;DR: In this article, the results are interpreted in terms of the single ion Hamiltonian including applied field, molecular field and crystal electric field (CEF) terms, and the B n m (n ≧4) terms were found to be dominant in this system.
Abstract: Magnetic studies have been performed on single crystals of the C-14 type Laves phase RRu 2 (R=Gd, Tb, Dy, Ho and Er) and the pseudo-binary (R 1- x Y x )Ru 2 (R=Tb, Dy, Ho and Er) compounds in the temperature rarxge from 4.2 K to 300 K. DyRu 2 shows a transition from cone structure to ferromagnetic one at 15 K and the other RRu 2 compounds exhibit ferromagnetism. The magntetization curves of the RRu 2 single crystals show their own characteristic behaviors dependent on the sort of R atoms. Lower moments for all RRu 2 compounds except GdRu 2 are observed at 4.2 K. The results are interpreted in terms of the single ion Hamiltonian including applied field, molecular field and crystal electric field (CEF) terms. From the analysis, the B n m ( n ≧4) terms were found to be dominant in this system. Tlne bi-quadratic exchange interaction seems to contribtate to magnetic properties in TbRu 2 and DyRu 2 .
TL;DR: In this paper, the magnetic properties of the ternary compounds Y(Fe-Co)2 with the cubic Laves phase structure are discussed in the rigid band model and concentration dependences of the magnetization, high-field susceptibility and the electronic low-temperature specific heat coefficient are calculated at 0 K.
TL;DR: In this paper, a new type of irradiation-induced phase transformation is presented in terms of displacement cascade formation and dynamic recovery at the structural interface that exists between the two phases.
Abstract: In Ti‐Cr alloys containing both the Laves phase (ordered TiCr2) and the β phase (bcc solid solution), 1 MeV Kr+ irradiation at temperatures <250 K amorphizes the Laves phase but not the β phase. The irradiation‐induced amorphous material transforms into polycrystalline β upon warming to room temperature. In contrast, irradiation at room temperature causes the β phase to grow by migration of the β/Laves interface; no change in local composition across the migrating interface is observed. The β phase also grows during prolonged irradiation at 100 K, but the velocity of the β/amorphous interface per unit calculated atomic displacement rate is more than three orders of magnitude lower than that of the β/Laves interface at room temperature. An interpretation of this new type of irradiation‐induced phase transformation is presented in terms of displacement cascade formation and dynamic recovery at the structural interface that exists between the two phases.
TL;DR: In this paper, the compounds RNiAl (R ≡ Sm − Lu, Y) with Laves phase structures (C14) were obtained from mixtures of the initial components by annealing at 1450-1500 °C and a pressure of 7.7 GPa.
Abstract: The compounds RNiAl (R ≡ Sm — Lu, Y) with Laves phase structures (C14) were obtained from mixtures of the powdered initial components by annealing at 1450–1500 °C and a pressure of 7.7 GPa.
Patent•
15 May 1987
TL;DR: In this article, an alloy which is expressed by a formula AB2, whose alloy phase substantially belongs to the Laves phase of an intra-metal compound, and whose crystalline structure is cubically symmetric C15 model with its crystal lattice constant staying in a range from 6.92-7.70Angstrom, is prepared as a main hydrogen absorbing/desorbing material.
Abstract: PURPOSE:To obtain a storage battery of high capacity and a long service life according to a method wherein the alloy phase of its electrode is specific to belong to the Laves phase of an intra-metal compound and its crystalline structure is cubically symmetric and consisting of an alloy whose crystal lattice constant has a specific length. CONSTITUTION:An alloy which is expressed by a formula AB2, whose alloy phase substantially belongs to the Laves phase of an intra-metal compound, and whose crystalline structure is cubically symmetric C15 model with its crystal lattice constant (a) staying in a range from 6.92-7.70Angstrom , is prepared as a main hydrogen absorbing/desorbing material. A in the formula represents one king or more than two kinds of element selected from among Ti, Zr, etc. B represents one kind or more than two kinds of element selected from among V, Cr etc. None of stable hydride phase or oxide phase can be generated even if the hydrogen absorbing/desorbing cycle is repeated because of large absorbed/desorbed amounts of hydrogen on account of a large number of hydrogen atom for occupying spaces among unit lattices. Thereby, it is possible to enlarge the capacity of the battery together with its excellent reversibility of reaction, while giving large effect on its long service life.
TL;DR: A detailed study of the magnetic properties of the cubic Laves phase compounds Ho(Co1-cRhc)2 with c = 0.02, 0.05 and 0.25 was made in this paper, with particular attention given to the nature of magnetic phase transitions.
TL;DR: In this article, an annealed and aged ferritic steel containing fine NbC precipitates and relatively coarse particles of Laves phase was bombarded with 4-MeV iron ions to 100 displacements per atom (dpa) at 400 to 600°C.
Abstract: An annealed-and-aged ferritic steel containing fine NbC precipitates and relatively coarse particles of Laves phase was bombarded with 4-MeV iron ions to 100 displacements per atom (dpa) at 400 to 600°C. Much of the damage structure consisted of dislocation tangles that coarsened with increasing temperature. Cavity formation began at 450°C, peaked at about 535°C, and was absent at 600°C. Maximum swelling was only 0.2%. The Laves particles exhibited recoil dissolution and restructuring. Bombardments with Fe + He + D or Fe + He beams at ratios of 10 atomic parts per million (appm) He/dpa and 45 appm D/dpa introduced high concentrations of very small bubbles and comparatively few larger, bias-driven cavities. The latter were initiated at bubble clusters on NbC particles. Maximum swelling of 0.75% occurred at 550°C. Recoil dissolution of the Laves phase was retarded by the gases. Large critical cavity sizes and unbalanced dislocation and cavity sink strengths contribute to low swelling of this alloy.