Laves Compounds Research Articles

Magnetostriction enhancement in Laves compounds (Sm,Yb)Fe 2

The magnetic and magnetostrictive properties of compounds (Sm 1− x Yb x )Fe 2 (0⩽ x⩽0.3) have been studied. When x<0.15, the compounds crystallize in the cubic structure of a C15 MgCu 2-type Laves phase. For x>0.15 a small amount of (Sm,Yb)Fe 3 compound with a PuNi 3-type structure appears and its amount increases with increasing Yb content. The magnetic ordering of 1 : 2 compounds is slightly strengthened by the substitution of Yb for Sm. Lattice parameters for Laves phase compounds keep almost unchanged for the whole range investigated, indicating the deviation from Vegard's law linear variation with composition. A magnetostriction enhancement of about 15% when x=0.05% both in spontaneous and polycrystalline magnetostrictions in Sm 0.95Yb 0.05Fe 2 has been observed, which can be ascribed to the anisotropy compensation effect.

Hyperfine Field and Induced Moment of 181Ta in the Rare Earth - Iron Laves Compounds

The hyperfine magnetic fields and their temperature dependence for 181Ta in ErFe2 and TmFe2 have been measured by the TDPAC method. Respectively, the following values were obtained at T ≈ 80 K: 16·3(2) T and 17·6(2) T. These data complete those for other RFe2 Laves phases (except CeFe2) obtained earlier and are discussed in common in the framework of the model predicting the induction of the localised 5d moment at Ta ions due to 5d-3d band hybridisation enhanced by the 4f-5d interaction.

A Laves phase-body-centered cubic structural relationship determined using high voltage electron microscopy

High energy electron and ion irradiation of a TiCr 2 Laves compound were found previously to result in a transformation to a body-centered cubic (bcc) solid solution. In the case of electron irradiation, the precipitating bcc phase exhibits preferential crystallographic orientation with respect to the initial compound crystal for irradiation temperatures above 200 K. This article presents an analysis of the electron diffraction data gathered in the course of the electron irradiation-induced Laves phase to bcc transformation in TiCr 2. A structural relationship between the bcc and Laves compound crystal lattices is determined which can account for all observations of preferentially oriented bcc precipitates. The significance of this mechanism for transformations between bcc and the Laves phases is discussed. In addition, the possible significance for deformation mechanisms of the Laves compounds is explored.

NMR study of laves compounds CeFe2, CeFe1.985Al0.015, and CeFe1.985Cu0.015

The hyperfine fields (HFF) at 57Fe, 27Al, and 63,65Cu nuclei in CeFe2, CeFe1.985Al0.015, and CeFe1.985Cu0.015 are measured by pulse nuclear magnetic resonance. While using the method of the HFF at a nonmagnetic impurity atom the main contributions to the experimental 57Fe and 63Cu HFF are estimated. The magnetic moments at 3d atoms are evaluated from the “local” contributions. The magnetic moments at Ce sites are estimated as well. They are: μ(Fe) = 1.44 + 0.03μB, μ(Ce) = − 0.58 + 0.05μB. The impurity Cu atom is considered to carry a magnetic moment in this compound. [Russian Text Ignored].

The Influence of Structural Similarity on Phase Transformations Between Bcc and the Laves Compounds

ABSTRACTA fundamental aspect of martensitic or order-disorder phase transformations is the maintainence of correspondences between atoms or atomic sites in parent and precipitate phases. The present work concerns a structural relationship between initial and final phases in a transformation which is neither martensitic nor order-disorder. A structural relationship between the C14 Laves compound structure and body-centered cubic (bcc) is presented based on electron diffraction recorded in the course of the electron irradiation-induced transformation of the TiCr2 Laves compound to the bcc (β) phase. The diffraction evidence indicates a preferential orientation of β with respect to the initial Laves phase. Consistent with the diffraction data, it is shown how the structures can be formed from one another via small displacements of atom positions. It is suggested that structural relationships in first-order transformations may be significant as paths of minimal structural rearrangement by which such transformations may occur.

X-ray photoelectron spectroscopy and Mössbauer study of Ho(Fe1−xMnx)2 compounds

Cubic Laves compounds Ho(Fe1−xMnx)2 (x=0, 0.1, 0.2, 0.3) were investigated by XPS and Mössbauer measurements. It was found that the binding energy (BE) of compounds obtained by XPS remains almost the same for all the compounds and no chemical shift (δ) of the core-electron binding energy was found, which implies that no charge transfer takes place from Mn atoms to Fe atoms due to Mn substitution. Mössbauer study has shown that the average hyperfine fields and the deduced Fe moment decrease with increasing Mn content. It is considered that the variation of isomer shift (IS) due to Mn substitution obtained by Mössbauer measurement is mainly due to the size effect since the isomer shift (δ) for the compounds are almost linearly dependent on the volume; electron transfers seem to be of minor importance.

Magnetic moment analysis of Ho(Fe 1- xMn x) 2 intermetallic compounds

Cubic Laves compounds Ho(Fe 1- x Mn x ) 2 ( x=0, 0.1, 0.2, 0.3) compounds were investigated by magnetization and Mössbauer measurements. It was found that the saturation magnetization of these compounds increases with increasing Mn content while the moment of the transition-metal sublattice drops upon Mn substitution. Also, Mn substitution can lead to a decrease of the R-T coupling strength according to molecular field theory calculations. From Mössbauer studies it was found that the average hyperfine-field and the deduced Fe moment decrease with increasing Mn content. Combined with magnetization measurements the moment of the Mn atoms was calculated and found to be rather small. It is suggested that the Fe moment is strongly influenced by the Mn atoms when the number of Mn atoms is above a critical value.

Variations of the amorphization temperature and particle size by hydrogen absorption in Er(Co1−xFex)2 pseudo-binary laves compounds

In this article, the amorphization temperatures and particle sizes of the pseudo-binary Er(Co[sub 1[minus]x]Fe[sub x])[sub 2] compounds are investigated as a function of the alloy composition, and related with hydrogen content and elastic modulus. Previously, it was reported that the ternary Er-Co-Fe system formed a homogeneous single phase with C15 cubic structure over the whole concentration range and absorbed a large amount of hydrogen at ambient conditions. Hydrogen concentration in Er-Co-Fe system had a maximum at the composition of x = 0.6, Er(Co[sub 0.4]Fe[sub 0.6])[sub 2]. Thus, the possibility exists of hydrogen-induced amorphization, and also of an effect of hydrogen concentration on the amorphization behavior.

The hyperfine magnetic field at57Fe and181Ta in Hf(Fe1−x Co x )2 system

The hyperfine magnetic field at57Fe in the ferromagnetic Laves compounds Hf(Fe1−x Cox)2 was measured by the Mossbauer effect method. The substitution of Fe atoms by Co atoms induces a gradual change ofBhf(Fe) and a decrease in the magnetic moment values in Fe−Co sublattice. The perturbed angular correlation measurements of181Ta were carried out forX=0,X=0.1,X=0.55 at 300 K, andX=0.4 atT=400°C. An abrupt change ofBhf (Ta) in 0<X<0.1 was observed.

Hyperfine fields and magnetic moments in laves compounds (Sc1−xAx)Fe2 (A=Y, Zr) with cubic structure

The experimental HFF data proved that the Sc-, Y- and Zr-atoms have the magnetic moments. The magnetic moments on Fe-sites and (Sc, Y)- or (Sc, Zr)-sites were estimated.

The Curie temperature and density of Fe&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;R amorphous alloys

Various kinds of Fe-R amorphous alloys have been prepared by a high-rate dc sputtering method in order to study the Curie temperature T c as a function of the de Gennes factor G for Fe 2 R, and to the difference of the density between amorphous and crystalline states. The exchange interaction between Fe-Fe in iron-light rare earth amorphous alloy systems of Fe 2 R persists and their Curie temperatures are lower than those crystalline counterparts. It should be noted that T c of Fe 2 Ce in the both states is much lower than that expected from the G vs. T c curve due to the valence fluctuation. In iron-heavy rare earth amorphous alloys of Fe 2 R, Fe-Fe exchange interaction becomes zero, being consistent with the results previously reported. The concentration dependence of the room temperature density shows a distinct anomaly around the composition corresponding to Fe 2 R. This difference between these two states is attributed to the denser packing structure of the Laves compounds. With increasing Ce content, the density of Fe-Ce amorphous alloy system increases although the density of Ce is lighter than that of Fe. This behavior is caused by the valence fluctuation of Ce in the alloy system.

Cerium compounds in the fashion of the light actinides

Researchers familiar with the light actinides easily recognize in cerium compounds a microcosm of the rich variety of properties seen in the light actinides. The parallelism seen between comparable cerium and actinide compounds strongly suggest that the same physical models are applicable. The most significant is the relative size of the f-orbital. Localization is generally tighter in Ce compounds than uranium compounds, making Ce roughly analogous to Np through Am. A way to see the actinide parallelism is to compare Hill plots. Compounds in the different regions of the plots (representing different physics) are isostructural compounds with the same companion (B) elements. The most common materials expected to exhibit direct f-f interaction are the cubic Laves compounds. Accordingly, we have determined the band structures of CeRu 2, CeRh 2, CeIr 2, and CeNi 2. Surprisingly it was found that an f-d interaction overshadows any direct f-f interaction in these systems. Compounds illustrative of the interaction of f-orbitals with “ligand” orbitals are the Cu 3Au structured materials. Materials calculated in this class are CeRh 3, CePd 3, and CeSn 3 - the materials of much interest as “mixed valent”. Although the focus is on the Ce compounds, calculations performed on uranium isomorphs are used to highlight the interesting physics.

Measurements of the hyperfine magnetic fields at Ta and Fe in the Laves compounds (Zrx Hf1−x)Fe2 for 0≤x≤1

The hyperfine magnetic fields at181Ta and57Fe in the ferromagnetic Laves intermetallic compounds (ZrxHf1−x)Fe2 (0≤x≤1) have been measured by the methods of TDPAC and Mossbauer effect, respectively, and shown to be practically independent of x at x≥0.4. An average value Bhf (Ta)=−6.52 T at 300 K was obtained for samples with x≥0.4, and −14.2 T for pure HfFe2 in the hexagonal C14 modification. For 0<x<0.4, a superposition of both field components was observed. A deviation of the temperature dependence of Bhf(Ta) in (Zr0.9 Hf0.1)Fe2 from that for Bhf (Fe) and the bulk magnetization was confirmed, studied in detail, and shown to exist for all x≥0.4. The temperature dependence of Bhf(Ta) in HfFe2 was close to that of Bhf (Fe).

The specific heat of two cubic laves compounds: TiBe 2 and ThMg 2

The low temperature specific heats of two isomorphous Laves compounds, TiBe 2 and ThMg 2, have been measured. The shape of the transition for the itinerant antiferromagnet TiBe 2 is characteristic of magnetic ordering; the entropy of this transition is quite small, approximately 107 mJ/mole-K, a further indication of itinerancy. The γ, proportional to the density of states, is 42 mJ/mole-K 2 for TiBe 2, and the Debye temperature, θ D, is 650 K. These numbers are compared to those for the itinerant ferromagnet, ZrZn 2. The results for ThMg 2 are γ=9.2 mJ/ mole-K 2 and θ D = 217 K. Results for both compounds are discussed in regards to the theory of Enz and Matthias.

Crystal field quenching of the Dy3+4f shell in the cubic Laves compounds (Dy1-xHox)Ni2and (Dy1-xYx)Al2

The Mossbauer effect in dysprosium 161 has been used to study crystal field quenching of the Dy magnetic moment in the Laves compounds (Dy1-xHox)Ni2 and (Dy1-xYx)Al2, via the measured quadrupole hyperfine parameter P. Very little change in the quenching of the 4f shell was observed in the (Dy1-xHox)Ni2 series and it is argued that this is a natural consequence of a large B4O40 term in the crystal field Hamiltonian. Rather more quenching occurs in the (Dy1-xYx)Al2 series, particularly when x approximately 0.6. Some estimates are given for the crystal field parameters B4 and B6 in the two sets of compounds.

Elastic properties of polycrystalline rare earth-cobalt laves compounds

Abstract The elastic moduli of the RCo2 compounds have been measured in the temperature raange between 4.2 to 300 K. A magneto-elastic lattice softening was observed in the magnetically ordered state. This effect is particularly large in NdCo2, SmCo2, and TbCo2. In addition NdCo2 and HoCo2 exhibit spin reorientations at 12 and 42 K, respectively, which appear as a narrow dip in the elastic moduli. At the Curie temperature of these compounds a prominent anomaly in the adiabatic compressibility is observed. The shape of the anomalies in the elastic moduli of these compounds is indicative of a first order transition observed in DyCo2, HoCo2, and ErCo2. The Curie temperature deducted from the elastic moduli is in satisfactory agreement with the temperature determined previously. The anomalous behavior of the elastic constants in the paramagnetic temperature range is attributed to crystal field effects of a similar character to that observed in RAl2 compounds.

Spin rotations in Ho xEr 1−xFe 2 cubic laves compounds

Spin rotations in Ho xEr 1−xFe 2 cubic laves compounds

Magnetic anisotropy and hyperfine interactions in CeFe2, GdFe2, and LuFe2

M\ossbauer-effect measurements on $^{57}\mathrm{Fe}$ have been carried out on the cubic Laves compounds Ce${\mathrm{Fe}}_{2}$, Gd${\mathrm{Fe}}_{2}$, and Lu${\mathrm{Fe}}_{2}$ between 80 and 300 K. The analysis of the M\ossbauer spectra allowed the determination of the easy axes of magnetization $\stackrel{\ensuremath{\rightarrow}}{\mathrm{n}}$ in these compounds. In Ce${\mathrm{Fe}}_{2}$, $\stackrel{\ensuremath{\rightarrow}}{\mathrm{n}}$ is parallel to the [100] direction up to 150 K; it then becomes of type [$\mathrm{uuw}$] with an angle of inclination with respect to the [100] axis of 20\ifmmode^\circ\else\textdegree\fi{}. Just below the Curie temperature at 230 K, this angle increases to 30\ifmmode^\circ\else\textdegree\fi{}. In Gd${\mathrm{Fe}}_{2}$, $\stackrel{\ensuremath{\rightarrow}}{\mathrm{n}}$ is parallel to the [100] direction at 80 and 300 K. In Lu${\mathrm{Fe}}_{2}$, $\stackrel{\ensuremath{\rightarrow}}{\mathrm{n}}$ is of [$\mathrm{uuw}$] type at 80 and 300 K. In terms of the phenomenological treatment of the magnetic anisotropy, the presence of an [$\mathrm{uuw}$] type of easy axis of magnetization indicates that the bulk magnetic-anisotropy constant ${K}_{3}$ is of the same order of magnitude as ${K}_{1}$ and ${K}_{2}$. The hyperfine parameters of the three compounds are reported and discussed.