Th2Zn17 Structure Research Articles

Effect of Substitution of Iron by Cobalt on the Physical Properties in the Sm2Fe14Mn3 Compound

The crystallographic and magnetic properties of Sm2Fe14—xCoxMn3 with x = 0, 1, 2, and 3 have been investigated using X-ray diffraction and magnetic measurements. The Sm2Fe14—xCoxMn3 samples crystallised in the rhombohedral Th2Zn17 structure. The unit cell volume decreases with increasing Co concentration. The Curie temperature as well as the saturation magnetisation increases with increasing cobalt contents. The Curie temperature of Sm2Fe11Co3Mn3 is about 470 K and the saturation magnetisation is about 160 emu/g. All the samples exhibit an easy direction of magnetization along the c-axis.

On the Structural and Magnetic Properties of R2Fe17?x(A,T)x (R = Rare Earth; A = Al, Si, Ga; T = Transition Metal) Compounds

R2Fe17 (R = rare earth) intermetallic compounds constitute one of the most important classes of materials identified as high-energy permanent magnet materials. They crystallize either in the rhombohedral Th2Zn17 structure (for light R) or in the hexagonal Th2Ni17 structure (for heavy R). In this article, we discuss the variations in the lattice parameters (unit cell volume), site occupancies and Curie temperature when non-transition and transition metals are substituted for Fe in R2Fe17 compounds.

Studies on structural transformation and magnetic properties in Sm2Co17 type alloys

Structural transformations and microstructural characterisation of Sm2Co17 alloys containing Fe, Cu and Zr at different stages of thermal processing have been investigated by X-ray diffraction, optical, scanning electron and transmission electron microscopes. Solution treated samples consist of a mixture of hexagonal TbCu7 (1:7 H) and rhombohedral Th2Zn17 (2:17 R) structure types of 2:17 phase. After isothermal aging, TbCu7 + Th2Zn17 structures transform into Th2Zn17 type structure with precipitation of Cu-rich hexagonal SmCo5 (1:5 H) and Zr-rich platelet phases. In addition to the main phases, a soft magnetic phase of composition Zr6(FeCo)23 is formed in alloys containing higher Zr composition. Isothermal aging studies reveal that magnetic properties show a peak value when aged at 1108–1123 K for 10 h. TEM studies show cellular precipitate structure with cell interiors having 2:17 R structure, while the fully coherent cell boundaries have the 1:5 H structure. Zr-rich platelets which run across many cells and cell boundaries were found to have 1:7 H structure.

A magnetic and crystallographic study of (Sm/Gd)2(Fe/Si)17Cz solid solutions

The crystallographic and magnetic properties of SmyGd2−yFe17−xSix (0⩽x⩽3 and y=1 and 1.5) solid solutions and their interstitial carbides have been investigated using x-ray diffraction and magnetic measurements. The SmyGd2−yFe17−xSix samples crystallized in the rhombohedral Th2Zn17 structure with less than 5 mol % of impurities. The unit cells of the mixed rare-earth (R) samples are smaller than those of Sm2Fe17 and Gd2Fe17. The carbided samples contain up to a total of 15 mol % of free iron, an iron silicide, and/or cubic Si5C3. The unit cells of the carbided samples are 1%–4% larger than those of the parent samples. For a given silicon concentration, the Curie temperatures (Tc) of SmyGd2−yFe17−xSix intermetallics are higher than those of the two end members. For example, the Tc of SmGdFe17 (280 °C) is approximately 160° and 80° higher than that of Sm2Fe17 and Gd2Fe17, respectively. The Tc measured for the SmyGd2−yFe17−xSix samples, 280–290 °C, are among the highest values observed for a R2Fe17−xMx intermetallic where M is a substituent other than cobalt. Except in the case of SmGdFe16SiCz (z unknown), the Tc of the carbided samples are 20%–25% higher than those of the parent samples. A Tc of 426 °C and a magnetization of 120.6 emu/g observed for SmGdFe16SiCz are the highest values measured for the intermetallics investigated herein. As determined by x-ray diffraction studies of magnetically aligned samples, the easy axis of magnetization is parallel to the c axis.

Hydrogen dynamics in the hydrides of Pr2Fe17 as revealed by Mössbauer spectroscopy

The rhombohedral Pr2Fe17Hx compounds with the Th2Zn17 structure have been prepared for x=0–5. Their lattice parameters and Curie temperatures have been determined from powder x-ray diffraction and thermomagnetic measurements, respectively, and their Mössbauer spectra have been measured between 4.2 and 295 K. The Mössbauer spectra for x=0, 1, and 2, obtained between 4.2 and 295 K, and those of Pr2Fe17H3, obtained above 90 K, have been analyzed with a seven sextet model, indicative of a basal magnetization in these compounds. The Mössbauer spectra of Pr2Fe17H3 below 90 K, of Pr2Fe17H4 between 4.2 and 295 K, and of Pr2Fe17H5 above 155 K, have been analyzed with a four sextet model, indicative of an axial magnetization in these compounds over the indicated temperature ranges. The axial magnetic anisotropy results from a combination of lattice expansion upon hydrogenation and contraction upon cooling, and the relative importance of the praseodymium Stevens coefficients. A magnetic phase diagram for the Pr2Fe17Hx compounds is proposed on the basis of their magnetic Mössbauer spectra. The Mössbauer spectra of Pr2Fe17H5 indicate that, above 155 K, the two hydrogen atoms occupying one third of the tetrahedral 18g sites are rapidly jumping, on the Mössbauer time scale of 100 ns, between the six available 18g positions, a jumping which slows down or ceases below 155 K. The compositional dependence of the hyperfine parameters of the Pr2Fe17Hx compounds indicates an initial filling of the interstitial 9e sites by the first three hydrogen atoms and then a subsequent filling of the interstitial 18g sites by the last two hydrogen atoms.

Comparison on the magnetic and structural properties of Sm(Co0.67−xFe0.25Cu0.06Zr0.02Cx)8.0, where x=0–0.15, melt spun ribbons and cast alloys

The effects of C additions on the phase transformation and magnetic properties of Sm(Co0.67−xFe0.25Cu0.06Zr0.02Cx)8.0, where x ranged from 0 to 0.15, melt spun ribbons and cast alloys have been studied by x-ray diffraction (XRD), differential thermal analysis (DTA), and vibrating sample magnetometer. In addition to the Th2Zn17 structure, two additional compounds, namely, the ZrC and SmCoC2, were detected by XRD after a thermal treatment over 700–1160 °C. The as-spun ribbons were highly crystalline at x=0 and became mostly amorphous at x=0.10. An intrinsic coercivity, Hci, of 3.0 kOe was obtained for the as-spun ribbons with x=0.05. After an optimum heat treatment, the Hci of the ribbons with x=0.01 was increased to 8 kOe. Cast alloys of identical chemical compositions were also solution treated and precipitation hardened. At x=0 for the cast alloy, a Br of 10.8 kG, Hci of 24 kOe, Hc of 9.8 kOe, and (BH)max of 27 MGOe, were obtained after an optimum heat treatment.

Microstructural Investigation of RE3(Fe.V) 29 (RE = Nd, Tb) Magnetic Materials

ABSTRACTThe microstructure of V stabilized RE3(Fe,V)29 (RE=Nd,Tb) has been investigated by transmission electron microscopy (TEM). The investigated samples were prepared by arc melting and subsequent annealing above 910°C. X-ray diffraction confirms that the samples can be indexed based on a monoclinic Nd3(Fe,Ti)29-type structure (3:29) with A2/m space group. Our TEM investigation confirms that Nd3(Fe,V)29 contains usually grains with 3:29 structure and A 2/m space group. In addition grains with rhombohedral Th2Zn17 structure are observed regularly. The Tb3(FeV)29 alloy consists also of grains with monoclinic Nd3(Fe,Ti)29-type structure and contains a high density of planer defects like crystallographic twins or antiphase boundaries. Twinning occurs preferably on (402) of the monoclinic 3:29 structure. No tetragonal RE(Fe,V)12 phase or Fe is found.

Neutron diffraction and Mössbauer spectral study of Nd2Fe16Ti and its nitride

The 295 K powder neutron diffraction patterns and the temperature dependence of the Mössbauer spectra of Nd2Fe17−xTix and Nd2Fe17−xTixNy have been measured. A Rietveld refinement of the neutron diffraction patterns yields the Nd2Fe16.32Ti0.68 and Nd2Fe16.32Ti0.68N2.7 stoichiometries for the two compounds and indicates that titanium occupies only the 6c crystallographic site and nitrogen only the 9e site in the rhombohedral Th2Zn17 structure. The insertion of interstitial nitrogen into Nd2Fe16.32Ti0.68 produces a 6.8% increase in the unit cell volume. The relative areas of the Mössbauer spectral components indicate that iron–iron, iron–titanium, and titanium–titanium 6c–6c dumbbell pairs exist in both of these materials. The magnetic hyperfine fields observed for the iron on the 6c site in the iron–titanium dumbbell pair in both compounds is substantially reduced from that found in Nd2Fe17 and Nd2Fe17N2.6 because of the titanium dumbbell near neighbor. For all the remaining hyperfine parameters there is a good correlation with those observed in Nd2Fe17 and Nd2Fe17N2.6. A linear increase is observed for the weighted average isomer shift with increasing unit cell volume for Nd2Fe17, Nd2Fe17N2.6, Nd2Fe16.32Ti0.68, and Nd2Fe16.32Ti0.68N2.7, because of the decreasing s-electron density at the iron-57 nucleus.

Effects of Ga substitution on structure and magnetocrystalline anisotropy of Tm2Fe17

A detailed investigation of the structure and magnetic properties of Tm2Fe17−xGax (x=0, 1, 2, 3, 4, 5, 6, 7, and 8) compounds has been performed by means of x-ray-diffraction, neutron-diffraction, magnetization, and ac-susceptibility measurements. Crystal-structure studies have shown that the prepared samples are single phase with the hexagonal Th2Ni17 for x⩽3 and the rhombohedral Th2Zn17 structure for x⩾5. In Tm2Fe13Ga4 the Th2Zn17 structure coexists with the Th2Ni17 structure. Substitution of Ga for Fe in Tm2Fe17 leads to an increase of the unit-cell volume, which is linear with the Ga concentration. In Tm2Fe17−xGax, the saturation magnetization at 1.5 K decreases linearly with increasing Ga content with a rate of 2.3 μB per substituted Ga atom. The Curie temperature is found first to increase with increasing Ga content, going through a maximum value of 485 K at about x=3, then to decrease. Between x=6 and 7, a minimum value of TC is reached and for higher x values TC increases again. X-ray-diffraction measurements on magnetically aligned Tm2Fe17−xGax powders show that the compounds with x⩽6 have an easy-plane type of magnetic anisotropy, whereas the compounds with x⩾7 exhibit easy c-axis anisotropy at room temperature. All Tm2Fe17−xGax compounds exhibit a spin-reorientation transition at low temperature, except for the sample with x=6, which shows an easy-magnetization direction perpendicular to the c axis in the temperature range from 5 to 300 K. For x⩽5, the spin-reorientation temperature is found first to increase with x and then to decrease, having a maximum value of 211 K at about x=3. In the samples with x⩾7, an easy-plane anisotropy was observed at low temperature, but an easy-axis preference of the magnetization at room temperature was observed. The results obtained for Tm2Fe17−xGax indicate that the mutually competing Tm- and Fe-sublattice anisotropies both change their sign with increasing Ga concentration.

Phase transformation and magnetic properties of Sm(Co0.91−xFexCu0.07Zr0.02)z powders for bonded magnet applications

Structural and magnetic properties of Sm(Co0.91−xFexCu0.07Zr0.02)8.0, where x=0, 0.12, 0.21, 0.29, and 0.32, and Sm(Co0.64Fe0.28Cu0.06Zr0.02)z, where z ranged from 6.9 to 8.6, have been systematically investigated by x-ray powder diffraction. It was found that most of these alloys exhibit a hexagonal Th2Ni17 structure with a space group P63/mmc after an optimum solid solution treatment with rapid quench. The fully processed materials (after precipitation hardening) all exhibit a rhombohedral Th2Zn17 structure with a space group of R3̄m as the primary phase. For Sm(Co0.91−xFexCu0.07Zr0.02)8.0, the lattice parameters, a and c, and cell volume, V, increase slightly at first with increasing x, and then more sharply when x is increased above 0.28. The latter drastic increase in lattice parameters and cell volume results in a sharp decrease in the Hci, Hc, and Hk values of fully processed materials. For Sm(Co0.64Fe0.28Cu0.06Zr0.02)z, the lattice parameters, a and c, and cell volume increase slightly when z is varied from 6.8 to 7.8, then exhibit a drastic decrease when z is further increased beyond 8.0. A Br of 11.3 kG, Hci of 27 kOe, and BHmax of 30 MGOe have been obtained on Sm(Co0.63Fe0.28Cu0.07Zr0.02)8.0 after a solid solution at 1160 °C and aging at 850 °C.

Effect of Ga substitution on the structure and magnetic properties of Ho2Fe17−xGax (x=0–8) compounds

The Rietveld analysis of x-ray diffraction data shows that Ho2Fe17−xGax (x=0–8) solid solutions crystallize with the Th2Ni17 structure for x⩽2, the Th2Zn17 structure for x⩾4, and the two coexisting phases for x=3. The unit-cell volume increases linearly with a slope of 8.7 Å3 per Ga atom. At lower gallium concentrations, Ga atoms occupy the 18f, 18h sites in the Th2Zn17 structure (or 12j, 12k sites in the Th2Ni17 structure) and avoid the 6c, 9d sites. For higher Ga content (x⩾6) Ga atoms still avoid the 9d site, but preferentially occupy 6c and 18f sites for x=6–8 while the occupancy factor of the 18h site decreases. Gallium substitution decreases the saturation magnetization linearly with a slope of 2.5μB. The compounds Ho2Fe17−xGax (x=7,8) possess uniaxial magnetocrystalline anisotropy at room temperature. Doping first increases, then decreases the Curie temperature until this finally rebounds for x>6. The “anomalous” enhancement of the Curie temperature for x=7, 8 may be correlated with the variation of the Fe–Fe bond lengths.

Dependence of magnetic properties on microstructure in mechanically alloyed Nd[sbnd]Fe[sbnd]Ti[sbnd

In the systems of NdxFe92−xTi8 and Nd8Fe92−yTiy, NdFeTi intermetallic compound with ThMn12 structure has been successfully synthesized by mechanical alloying (MA) and subsequent annealing. It has been found that the ThMn12 structure exists only over a range of compositions 5 ⩽ x < 11 and < y < 16 for NdxFe92−xTi8 and Nd8Fe92−yTiy, respectively, annealed at 960°C for 30 min. The Th2Zn17 structure for x ⩾ 11 as well as for either y = 2 or y > 16 and the TbCu7 structure for y = 4 can be formed, respectively. For Nd8Fe84Ti8, MA powder annealed at 650–850°C, the phase of hexagonal TbCu7 structure is formed. With increasing the annealing temperature Ta, the metastable TbCu7 structure is transformed into the ThMn12 structure. The Curie temperature increases from 180°C for the TbCu7 structure at Ta = 650°C to 300°C for the ThMn12 structure at Ta = 1050°C. The nearly complete transformation from TbCu7 to ThMn12 may be achieved at Ta = 960°C. All the MA prepared samples are nitrided at TN = 400°C for 15 h and the nitrogenation raises the Curie temperature Tc of the phase with the ThMn12 structure to 400–450°C. Too high temperature of the nitrogenation leads to decomposition of the compounds. The dependence of the magnetic properties on the composition and heat treatment and nitriding conditions has been studied.

Structure and magnetic properties of Nd2Fe17–xMnx compounds (x = 0 to 8)

The effect of Mn on structure and magnetic properties of Nd2Fe17-xMnx compounds has been studied. Substitution of Mn for Fe does not change the structure of Nd2Fe17 and all the investigated Nd2Fe17-xMnx compounds (x = 0 to 8) crystallize in Th2Zn17 structure. Upon substitution of Mn, the lattice constants decrease after a small initial increase. and then increase again. Substitution of Mn for Fe causes a monotonous decrease of the Curie temperature. The saturation magnetization of Nd2Fe17-xMnx compounds decreases dramatically with increasing Mn content. The moments of the Mn atoms in these compounds are also discussed.

Mössbauer study of permanent-magnet R2Fe17−xMxCy compounds

We report Fe57 Mössbauer spectroscopy studies of the effect of carbon doping on the magnetic properties of the Fe sites of R2Fe17−xMxCy, and of the presence of multiple phases in these systems. In this study two systems, Sm2Fe14Al3Cy, where y=0, 1.0, 2.0, and 3.0, and Nd2Fe14.54Si2.46Cy, where y=0, 0.432, and 2.544, were measured at room temperature and analyzed. The ternary compounds R2Fe17−xMxCy studied here have the rhombohedral Th2Zn17 structure with c-axis anisotropy. The Al and Si site occupation used in the fitting were taken from previous results. Analysis of the Mössbauer spectra showed that the hyperfine fields for the different sites decreased in the order 6c, 9d, 18f, and 18h. The average hyperfine field for Sm2Fe14Al3Cy was found to increase with increasing carbon concentration, which is in qualitative agreement with magnetic measurements. For Nd2Fe14.54Si2.46Cy the average hyperfine field was found to increase for low C concentration and decrease for high C concentration; this behavior is in agreement with our magnetization measurements. The measured average isomer shift relative to α-iron was found to increase with y. In these compounds alloying with C and/or M can improve the magnetic properties such as Curie temperature and magnetization which make them potential candidates for permanent magnet development.

Structural and magnetic studies of Er2Fe17−xMxCy (M=Ga and Al) compounds

The effect of Ga and Al substitution for Fe on the structural and magnetic properties of the Er2Fe17−xMxCy (M=Ga, Al; x=0–4, y=0–2) compounds was investigated. It was found that Ga is superior to Al in stabilizing the single-phase Er2Fe17−xMxCy compounds. The hexagonal Th2Ni17-type structure persisted in almost all alloys with the exception of Er2Fe13Ga4C and Er2Fe13Ga4C2. These two compounds exhibited a rhombohedral Th2Zn17 structure. Both the Curie temperature and magnetization can be enhanced with a certain amount of Ga or Al substitution. But they decreased almost monotonically with the increase of Ga or Al content in Er2Fe17−xMxCy (x≳1, y≳0). The spin reorientation temperature, Tsr, was influenced by both carbon interstitial and Ga or Al substitution for Fe and ascribed to the increase of the c-axis uniaxial anisotropy of the Er3+ sublattice by the modification of electron structure around it. The highest Tsr of 241 K appears in the compound Er2Fe14Ga3C.

メカニカルグラインディング法によるSm&lt;SUB&gt;2&lt;/SUB&gt;Fe&lt;SUB&gt;17&lt;/SUB&gt;N&lt;I&gt;&lt;SUB&gt;x&lt;/SUB&gt;&lt;/I&gt;粉末作製に及ぼすミル雰囲気の影響

The preparation of Sm2Fe17Nx permanent magnet powders has been tried by mechanical grinding (MG) for a short time without crystallization heat treatment which was usually needed to obtain a Th2Zn17 structure in the conventional method by MG or MA. MG was carried out in three kinds of atmospheres; i.e., Ar, N2 and NH3 gas. Non-treated and hydrogenated Sm2.5Fe17 alloy powders were used as the starting materials. The α-Fe precipitation was detected in the powder after MG for over 14.4 ks. The grain size of powder obtained by MG for 10.8 ks was around 10 nm which was much finer than the single magnetic domain size of about 300 nm. The existence of hydrogen promoted not only the nitriding of powders but the oxidation. The hydrogenated powder after MG in NH3 and nitriding had a high oxygen content of about 13000 ppm. This oxidation prevented the absorption of nitrogen during the nitriding process. The non-treated powders after MG in NH3, however, were nitrided efficiently up to 38000 ppm at a low temperature of 623 K, and the oxygen content was about 7000 ppm. The maximum coercivity of 0.93 MA·m−1 (11.7 kOe) was obtained with the non-treated powder after MG in NH3 and nitriding at 623 K for 10.8 ks in N2.

ＭＧ法により作製したＳｍ２Ｆｅ１７Ｎｘ粉末の磁気特性の改善

The preparation of Sm2Fe17Nx permanent magnet powders was tried by mechanical grinding (MG) and the subsequent nitriding without crystallization heat treatment which was usually needed to obtain Th2Zn17 structure in the conventional method by MG or mechanical alloying (MA). MG was carried out in NH3 gas with a rotary ball mill. The powder after MG for 324ks (90hr) had the sufficient nitrogen content of about 35000ppm. The magnetic properties of this powder, however, was insufficient because of the influence of distortion introduced during MG. In order to decrease the distortion, powders were prepared by MG for short time of 18ks-72ks (5hr-20hr). Although these powders contained an insufficient nitrogen of around 10000ppm, nitriding at 723K for 21.6ks in N2 raised nitrogen content up to 35000ppm. The powder after MG for 18ks and the subsequent nitriding showed the good rectangularity in the demagnetization curve. From this curve, the saturation magnetization and the remanence were confirmed to be about 1.23Wb⋅m-2 and 1.06Wb⋅m-2, respectively.

Mössbauer studies of interstitial intermetallics

After an introduction to interstitial incorporation of 2p elements in iron-based alloys, the main physical effects of these interstitials on the intrinsic properties of rare-earth intermetallics are outlined. Then follows a survey of the results obtained using the57Fe and several rare-earth resonances for rare-earth intermetallics with the Th2Zn17, Th2Ni17, ThMn12 and BaCd11 structures in which nitrogen or carbon has been interstitially incorporated. The results of Mossbauer studies in this area are discussed, and future prospects are assessed.

Neutron-diffraction and Mössbauer effect study of the Tb2Fe17−xAlx solid solutions

The magnetic properties of a series of Tb2Fe17−xAlx solid solutions, with nominal x compositions of 0, 2, 3, 4, 5, 6, 7, and 8, have been studied by neutron diffraction and Mössbauer spectroscopy. Neutron-diffraction data indicate that the compounds all crystallize with the Th2Zn17 structure and that the aluminum atoms are excluded from the 9d site and show a distinct preference for the 6c site only for an aluminum content greater than 6. The unit-cell volume increases by approximately 1% per aluminum atom substituted in the formula unit. The magnetic moment per formula unit, measured at 295 K, shows very little change for x less than or equal to 4, but decreases rapidly with increasing aluminum content for higher values of x. Mössbauer spectral results indicate that all the samples are ferromagnetically ordered at 85 K. However, at 295 K Tb2Fe9Al8 is paramagnetic and Tb2Fe10Al7 is either paramagnetic or has at most very small ferromagnetic moments. An analysis of the magnetic spectra with a basal magnetic model is successful for x values of 5 or less; however, at higher x values an axial model for the magnetization is required, indicating the presence of a spin reorientation with increasing aluminum content and decreasing temperature. The weighted average hyperfine field decreases approximately linearly by 21 kOe per substituted aluminum atom at 85 K and more rapidly at 295 K. As expected, the isomer shifts increase with increasing aluminum content as a result of interatomic charge transfer and intraatomic iron 4s-3d electronic redistribution.

Mössbauer study of permanent-magnet materials: Sm2Fe17−xAlx compounds

The Fe57 Mössbauer spectra of Sm2Fe17−xAlx, where x=0, 1.0, 2.0, 3.0, and 4.0, have been measured at room temperature and analyzed. The ternary compounds Sm2Fe17−xAlx have the rhombohedral Th2Zn17 structure. Mössbauer measurements showed that all the compounds studied were ferromagnetic. The average hyperfine field was found to decrease with the increasing aluminum concentration, which is in qualitative agreement with magnetic measurements. The decrease in the average hyperfine field was from 224 kOe at x=0 to 174 kOe at x=4. By fitting the spectra we found that the hyperfine fields for the iron sites decrease in the order 6c, 9d, 18f, and 18h. The measured average isomer shift relative to α-iron was found to increase linearly with x. Analysis of the spectra showed that Al atoms occupy the 6c, 18h, and 18f, but not 9d, Fe sites and the fraction of occupancy of Al was found to depend on x.