Rare-earth Iron Intermetallic Compounds Research Articles

Development of novel Gd-Fe/Ti composites with tunable thermal expansion property

Abstract Titanium alloys are considered one of the most promising materials. However, their poor thermal expansion property remains a major obstacle to their widespread application. In this study, we explored an innovative design strategy to tune the thermal expansion properties of titanium alloy. Specifically, we used rare earth iron intermetallic compounds (Gd-Fe IMCs) with low coefficient of thermal expansion (CTE) as expansion inhibitors to prepare composites with the required thermal expansion properties via in situ reaction. The morphology and size of Gd-Fe IMCs can be effectively controlled by electromagnetic and ultrasonic fields, resulting in a dense distribution of micro/nano-structured Gd-Fe IMCs and strong interfacial bonding of the composites. This alloy has an excellent CTE of 6.8 × 10−6/K and a high ultimate tensile strength of 921 MPa. The improvement in the physical properties (especially in thermal expansion properties) of titanium alloy can be attributed to the synergistic effect between Gd-Fe IMCs and Ti matrix. This design strategy can also be extended to other titanium alloys as a reference for designing low thermal expansion titanium alloys.

Hyperfine interactions in R x Gd1− x Fe3 intermetallics R = Tb, Y

The structural and magnetic properties of rare earth iron intermetallic compounds TbxGd1−xFe3 and YxGd1−xFe3 (x = 0. 0, 0. 1, 0. 2, 0. 4, 0. 5, 0. 6, 0. 8, 1. 0) was studied by X-ray diffraction, the 57Fe Mossbauer effect and SQUID measurements. All investigated compounds crystallize in the rhombohedral PuNi3-type of crystal structure. The investigation of magnetic properties of RxGd1−xFe3 proved their ferrimagnetic behavior. The Curie temperature of the investigated compounds decreases with the increase of R concentration from 721K (GdFe3) to 655K (TbFe3) and 533K (YFe3). The saturation magnetic moment MS in the RxGd 1−xFe3 system increase with x parameter. The Mossbauer spectra are analyzed using four sextets, corresponding to three crystallographically (b, c, h) and four magnetically (b, c, h1, h2) inequivalent sites for iron. The mean hyperfine magnetic field increases with increase of the Gd concentration

Origin of the anomalous contributions to the ac magnetic susceptibility of rare-earth–iron intermetallic compounds

A systematic ac magnetic susceptibility, ${\ensuremath{\chi}}_{\text{ac}}(T)$, study has been performed on several ${R}_{2}{\text{Fe}}_{14}{\text{BH}}_{x}$ ($R=\text{rare}$ earth) compounds in order to determine the origin of the anomalous behavior of ${\ensuremath{\chi}}_{\text{ac}}(T)$ not related to spin reorientation transitions---the so-called non-SRT anomalies. All the measurements have been performed on magnetically oriented samples to identify the anomalies due to domain-wall displacements. Different types of non-SRT anomalies have been found. It has been found that the anomalous behavior is mainly due to the existence of mobile defects coupled to the domain walls, which existence has been confirmed by performing magnetic aftereffect measurements. However, this mechanism alone cannot explain the whole phenomenology and other influences on ${\ensuremath{\chi}}_{\text{ac}}(T)$ have to be taken into account to correctly describe the non-SRT anomalies. Specifically, three situations are possible when analyzing the anomalous behavior of ${\ensuremath{\chi}}_{\text{ac}}(T)$: (1) compounds with no magnetic $R$ anisotropy, in which the non-SRT anomalies are due to the existence of one or more mobile defects coupled to the domain walls, (2) compounds in which a large magnetic $R$ anisotropy can influence the domain-wall mobility at very low temperatures, and (3) compounds in which a large magnetic $R$ anisotropy and the existence of SRTs can influence the response of the domain walls coupled to mobile defects. Different fitting models have been proposed for each case.

Mössbauer spectral study of theRFe11.5Ta0.5(R=Tb,Dy,Ho,Er,andLu)compounds

The paper presents an iron-57 M\"ossbauer spectral study of $R{\mathrm{Fe}}_{11.5}{\mathrm{Ta}}_{0.5}$, with $R=\mathrm{Tb},\phantom{\rule{0.3em}{0ex}}\mathrm{Dy},\phantom{\rule{0.3em}{0ex}}\mathrm{Ho},\phantom{\rule{0.3em}{0ex}}\mathrm{Er},\phantom{\rule{0.3em}{0ex}}\mathrm{Lu}$, and an evaluation of the different contributions to the hyperfine magnetic fields. The M\"ossbauer spectra have been analyzed with a model that considers both the distribution of the tantalum atoms in the near-neighbor environment of the iron atoms and the relative orientation of the hyperfine field and the principal axis of the electric field gradient. Their possible directions in the ${\mathrm{ThMn}}_{12}$ structure have been determined from a close examination of the point symmetry of each iron site. A local model for the hyperfine field which enables to determine their components from experimental data, has been developed and a calculation of the lattice dipolar hyperfine field in $R{\mathrm{Fe}}_{11.5}{\mathrm{Ta}}_{0.5}$ has been performed. We have investigated in detail the origin and influence of the contributions to the hyperfine field coming from self $3d$ polarization, the iron and rare earth transferred fields and the orbital and dipolar hyperfine fields. The iron and rare earth transferred fields have been analyzed for $R{\mathrm{Fe}}_{11.5}{\mathrm{Ta}}_{0.5}$ and other rare earth-iron intermetallic compounds. From this analysis it is shown that the iron transferred fields are different at each crystallographic site, and comparable to the self $3d$ polarization contributions, and that the rare earth transferred field is mainly originated by the indirect exchange between the rare earth $4f$ and iron $3d$ electrons.

Frequency dispersion of complex permeability and permittivity on iron-based nanocomposites derived from rare earth-iron intermetallic compounds

Complex permittivity, permeability, and electromagnetic wave absorption properties of resin compacts containing 80 wt% composite powders of α-Fe/Y 2O 3 and ɛ-Fe 3N/Y 2O 3 were characterized by a conventional reflection/transmission technique. The real and imaginary parts ( ε ′ r and ε ″ r ) of relative permittivity for these resin compacts almost kept low constant between 0.5 and 10 GHz. The imaginary part ( μ ″ r ) of relative permeability exhibited a peak in the 1–5 GHz range on the α-Fe/Y 2O 3 resin composites, while “twin peak” dispersion in the 0.5–5 GHz range on the ɛ-Fe 3N/Y 2O 3 ones. The resin composites of α-Fe/Y 2O 3 and ɛ-Fe 3N/Y 2O 3 powders with thicknesses of 3.0–5.0 and 3.3–19.3 mm provided good electromagnetic wave absorption performances (reflection loss <−20 dB) in ranges of 2.0–3.5 and 0.6–4.4 GHz, respectively.

Reversible nitrogen absorption and desorption on rare earth–iron intermetallic compounds

Nitrogen absorption and desorption characteristics on rare earth–iron intermetallic compounds, R 2Fe 17 and RFe 7, were performed. These intermetallic compounds absorbed nitrogen into their crystal lattices by heating in NH 3 or N 2 gas at 573–773 K to form the interstitial-type metal nitrides. The nitrogen stored in the metal nitrides was reversibly released by a successive heat treatment in a stream of H 2 gas at 523–723 K. The nitrogen absorption and desorption properties of RFe 7 was superior to that of R 2Fe 17 because of the ease of nitrogen diffusion due to the difference of crystal structure between them. The nitrogen absorbed in the lattice of both compounds exists as an atomic state, so that the nitrogen desorbed from the compounds readily reacted with hydrogen to form ammonia during the nitrogen desorption.

Synthesis of Structure and Surface Functional Rare Earth Materials.

Structure and surface functional rare earth materials were synthesized and their physicochemical properties were characterized to design high-performance materials, viz. (1) Efficient phosphors, (2) persistent spectral hole burning devices, (3) permanent magnets and (4) nitrogen storage materials: (1) Strontium borates consisting of BO4 units, SrB4O7 and δ-SrB2O4 (high-pressure phase), were good host lattices to provide intense blue emissions owing to the lowered phonon effect of three-dimensional BO4 network. (2) Persistent spectrum hole burning spectra were observed on the sol-gel-derived silica-based glasses dispersed with europium(III) crown ether complex, of which the mechanism was based on the reduction of Eu3+ ions. (3) Rare earth intermetallic compounds such as Sm2Fe17Nx (x = ∼3) and Nd2Fe14B provided high-performance bonded magnets by effective surface coating for the raw fine powders, Zn metal vapor sorption and/or silylation with alkyl silane. (4) Nitrogen storage systems were established by nitrogenation and denitrogenation cycle between the rare earth-iron intermetallic compounds and metal nitrides, by which ammonia was formed even at ambient pressure.

Crystal growth of rare earth–iron intermetallic compounds by the flux-creep-up method

A new flux method for the crystal growth of rare earth–iron intermetallic compounds was developed. In this method, the rare-earth flux creeps up the inner surface of a BN-coated crucible during the cooling process, and free-standing crystals are left on the bottom of the crucible. This method was applied to the crystal growth of compounds in Sm–Fe and Nd–Fe systems, and crystals of SmFe 2, SmFe 3, Sm 6Fe 23, and Nd 6Fe 13− x Al 1+ x were grown for the first time. In particular, SmFe 7 is a new phase in the Sm–Fe system with high performance as a permanent magnet. Since the chemical composition of the mixture in the crucible changes in accordance with the creep-up of the flux, this method may be promising in the search for new phases as well as for the crystal growth of known materials.

Magnetic structure and Fe moment distribution in rare-earth iron intermetallic compounds by first-principles calculations

The magnetic properties and Fe moment distributions in a variety of rare-earth Fe compounds are studied by first-principles spin-polarized calculations. Examples are Y 2Fe 14B, Nd 2Fe 14B, Y 2Fe 17, Nd 2Fe 17, Nd 3Fe 29 and most recently, Nd 5Fe 17 phases. Also studied are substitutions by transition metal and metalloid elements, and by doping with C or N in some of these compounds. The newly discovered Nd 5Fe 17 phase with a Curie temperature above 500 K is particularly interesting because of its complex structure. It has 14 different Fe sites and seven different Nd sites of varying local coordination and nearest-neighbor distances. Based on the results of calculations on Nd 5Fe 17 and Nd 3Fe 29 phases, it is concluded that Fe moments on individual sites correlate more with the number of nearest-neighbor Fe atoms and less with the average distance of Fe–Fe separations.

Nitrogen storage properties based on nitrogenation and hydrogenation of rare earth–iron intermetallic compounds R2Fe17 (R=Y, Ce, Sm)

Abstract The nitrogen storage properties for the rare earth–iron intermetallic compounds, R 2 Fe 17 (R=Y, Ce, and Sm), were investigated. These intermetallic compounds formed the corresponding metal nitrides by heating in a mixed gas of NH 3 –H 2 at 350–450°C and the nitrogen was incorporated into interstitial sites of the crystal lattices. The nitrogen stored as the metal nitrides was reversibly released as NH 3 by the following heating in H 2 at 450°C. An amount of the nitrogen released per unit volume of these intermetallic compounds is larger than that of a conventional nitrogen container charged at 15 MPa. The nitrogen storage capacity of Sm 2 Fe 17 N x was increased by repeating the nitrogenation–hydrogenation cycle owing to the formation of FeN x /RN y composites with large surface areas derived from the starting intermetallic compound through the cycle. Furthermore, the nitrogen storage characteristics of Sm 2 Fe 17 powders were effectively improved by surface loading with Ru metal that is active for ammonia generation.

Gas-phase modification of rare-earth intermetallic compounds

Recent work concerning the interstitial modification of permanent magnet alloys based on rare-earth iron intermetallic compounds is reviewed. The crystal structure of the new materials is discussed, then the thermodynamic and statistical aspects of the low-temperature interstitial modification process are considered. Finally, reaction kinetics and thermal stability of the new compounds are discussed and future prospects assessed.

High Pressure Synthesis and Magnetostrictive Measurement of Laves Phase Pr1-xRxFe2 (R=Ce, Nd)

Laves phase rare-earth iron intermetallic compounds were synthesized under high pressure and high temperature by using a double stage multianvil high pressure equipment. The minimum pressure required to synthesize the Laves phase was determined. The maximum magnetostriction of 8×10-6 was attained at room temperature for PrFe1.8.

New interstitial rare-earth iron intermetallics produced by gas phase reaction

New rare-earth iron intermetallic compounds have been generated from existing series by the reaction of powder with an appropriate gas. Interstitial atoms occupy sites adjacent to the rare earth, creating a crystal field that reflects the new local symmetry. They also expand the lattice, which leads to an increase in iron moment due to narrowing of the 3d bands and modifies the Fe-Fe exchange interactions, resulting in increases of the Curie temperature of 200–400 K. These effects are discussed with reference to the system R 2Fe 17Z 3−δ where Z=N, C, B. The observed volume dependence of the magnetic moment at the four inequivalent iron sites of Y 2Fe 17, due to interstitial modifications with nitrogen and carbon, are compared to calculated values published for pure Y 2Fe 17. Details of the nitrogenation process and of the broad line shapes observed in nitrided materials are discussed with reference to the compound Sm(Fe 11Ti)N 1−δ.

Intrinsic magnetic properties of new rare-earth iron intermetallic series

New rare-earth iron intermetallic compounds have been generated from existing series by the reaction of powder with an appropriate gas at about 500°C. Interstitial atoms 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 modifies the Fe-Fe exchange interactions and may increase the iron moment by narrowing the 3d bands. These effects are discussed with reference to three systems: R 2Fe 17N 3-δ, R 2Fe 17C 3-δ and R(Fe 11Ti)N 1-δ. Increases of Curie temperature of 300–400 K are achieved on nitrogenation or carbonation of R 2fe 17, whereas the increases in the 1:12 compounds are approximately 200 K. The sign of A 0 2, the second-order crystal-field coefficient at rare-earth sites, is opposite in the 2:17 and 1:12 interstitial compounds.

Magnetic coupling in rare earth-iron intermetallic compounds

Magnetization measurements have been performed at 4.2 K in semicontinuous fields up to 35 T on free powders of ferrimagnetically-ordered Er2(Fe, Mn)17C and (Er, Y)6Fe23 compounds. The field-induced non-collinearity of the Er- and T-sublattice magnetizations provides information regarding the Er-T interaction strength JErT. The JErT values derived in this way are compared with values of the interaction strength obtained by means of analysis of the Curie temperatures.

Intrinsic magnetic properties of SmTiFe10

The rare-earth–iron intermetallic compounds SmTiFex, with x ranging between 8 and 10, have been synthesized by an arc-melting technique. We found that they crystallize in the ThMn12-type tetragonal structure, I4/mmm. Unusual uniaxial magnetocrystalline anisotropies have been observed. The c axis is the easy magnetization direction. Curie temperature is 610 K. After the discovery of the R2Fe14B compounds, we have other ternary rare-earth–iron intermetallic compounds with strong uniaxial anisotropy.

Invar effect in rare earth-iron intermetallic compounds

For rare earth compounds with iron a comparison is presented between the results of band-structure calculations and experimental data available at present. The magnetovolume effects like the forced and spontaneous magnetostriction and the pressure dependence of the Curie temperature in combination with the high-field susceptibility can be interpreted by band effects and involve a large volume dependence of the band-structure parameters.

STRUCTURAL AND MAGNETIC PROPERTIES OF Sm (Ti, Fe)12 INTERMETALLIC COMPOUNDS

The rare earth-iron intermetallic compounds of SmTiFex with x ranges from 8 to 11, was synthesized by are-melting technic. We found that they crystallize in the ThMn12-type tetragonal structure, 14/mmm. We report here the crystallographic and magnetic properties of Sm(Ti, Fe)12 and Gd (Ti, Fe)12. Unusual uniaxial magnetocrystalline anisotropy was observed in Sm(Ti, Fe)12 compounds. For Sm(Ti, Fe)12, the c-axis is the easy magnetization direction, and Curie temperature is 610 K. The magnetizrystalline anisotropy of Sm and Fe sublattices in Sm(Ti, Fe)12 compounds was analyzed by measuring magnetization curves of Gd(Ti, Fe)12. On the basis of our data, we conclude that both Sm and Fe sublattices have easy axis. After the discovery of Nd2Fe14B magnets, Sm(Ti, Fe)12 is another ternary rare earth-iron intermetallic compounds with strong uniaxial anisotropy.

Hydrogen absorption characteristics of oxygen-stabilized rare-earth iron intermetallic compounds

The thermal behavior of oxygen-stabil ized RjFegO^-hydrogen (R = Y, Dy, Ho) systems was studied by means TGA-DTA techniques. The results were compared to those obtained on binary RFe2 and RFe3 compounds.