ThMn12 Structure Research Articles

The origin of high magnetic properties in (R,Zr)(Fe,Co)11.0–11.5Ti1.0–0.5Ny (y=1.0–1.4 for R=Nd, y=0 for R=Sm) compounds

Ten alloys and nitrogenated compounds of (R,Zr)(Fe,Co)11.0–11.5Ti1.0–0.5Ny (y=1.0–1.4 for R=Nd, y=0 for R=Sm) with a ThMn12-type structure were prepared. The average Fe–Fe interatomic distances, d(Fe–Fe), for Fe sites were calculated based on the reported atomic parameters. The hyperfine splittings (inner field (IF), in teslas) were measured by Mössbauer spectroscopy, and the IF increased with increasing d(Fe–Fe) for Fe sites, indicating a magneto-volume effect. The order of IF magnitude in Fe sites was Fe(8i)>Fe(8j)>Fe(8f) in all alloys. Co substitution for Fe sites, (Fe0.75Co0.25), increased the IF by 25% for the R=Nd alloy and 15% for the R=Sm alloy. Decreasing Ti content from −Ti1.0 to −Ti0.5, which increased the Fe and Co content, preserved the ThMn12 structure with Zr substitution for R(2a) sites, and caused a slight increase in the IF of 2% for the R=Nd alloy and 7% for the R=Sm alloy. Nitrogenation, where N was introduced into the 2b sites, also increased IF in R=Nd alloys, by 23% for the Co- and Zr-free alloys, NdFe11Ti1.0N1.5, and by 7% for the Co-containing, (Nd0.7Zr0.3) (Fe0.75Co0.25) 11.5Ti0.5N1.3 alloy. The IF values of the R=Nd alloys were slightly larger than those of the R=Sm alloys. In conclusion, the magneto-volume effect was clearly observed at the Fe sites, and Co substitution into Fe sites and nitrogenation (R=Nd alloys) compensated for the increased IF. Increasing the Fe and Co fractions also increased IF slightly.

The stability of newly developed (R,Zr)(Fe,Co)12−xTix alloys for permanent magnets

(R,Zr)(Fe,Co)12−xTix (R = Nd and Sm) alloys of ten different compositions were prepared by strip-casting. The elemental distribution of the sample particles after annealing was quite homogeneous. Existing phases in the prepared alloys were determined by X-ray diffraction and the occupation sites of the substituted elements (Ti, Co, and Zr) were determined using spherical aberration corrected scanning transmission electron microscopy. The ThMn12 structure is stable in Ti1.0 compounds for both R = Nd and Sm, but exhibited obvious precipitation of α-(Fe,Co) phases in low Ti content compounds with Ti0.5. Ti substitution into Fe(8i) sites is important for the stabilization of the ThMn12 structure. Furthermore, the stability of low Ti content compounds could be recovered by the substitution of Zr into R(2a) sites. Co was mainly in Fe(8j) and Fe(8f) sites, which contributed to the stability of the 1–12 structure by increasing the configuration entropy. Analysis based on three Fe hexagons and two local sub-structural units suggested that the stabilization of ThMn12 structure by Ti and Zr substitutions mainly originates by resolving local mismatches in interatomic distances in the structure.

ThMn12-type structure and uniaxial magnetic anisotropy in ZrFe10Si2 and Zr1−Ce Fe10Si2 alloys

Abstract Arc-melted (Zr1−xCex)1.1Fe10Si2 alloys were found to crystallize into a pure or nearly pure ThMn12 structure for 0 ≤ x ≤ 0.6. At room temperature, the alloys exhibit ferromagnetism with an uniaxial magnetocrystalline anisotropy. Metastable ZrFe10Si2 compound possesses room-temperature saturation magnetization of at least 11 kG and Curie temperature of 325 °C; both properties slightly decrease when Ce is being substituted for Zr. The anisotropy field, on the other hand, increases with the Ce from 16.9 to 24 kOe at x = 0.6. These intrinsic magnetic characteristics as well as the absence of expensive rare-earths and Co make the compounds interesting for development of low-cost permanent magnets. At 0.7 ≤ x ≤ 0.8, the ThMn12 structure was found to co-exist with the Th2Ni17-type structure, whereas the equilibrium Th2Zn17-type structure was observed only at x = 1. Prepared under similar conditions Hf1.1Fe10Si2 alloy does not crystallize into the ThMn12-type structure.

A new magnet material with ThMn12 structure: (Nd1−xZrx)(Fe1−yCoy)11+zTi1−zNα (α=0.6–1.3)

We previously reported a new compound for permanent magnets, (Nd0.7Zr0.3)(Fe0.75Co0.25)11.5Ti0.5N0.56, which has a high saturation polarization (Js) of 1.68T and a high magnetocrystalline anisotropy field (Ha) of 2.88–4.0MA/m. Here, we examined the effects of substituting Co and Ti at the Fe sites and Zr at the Nd sites. Js increased with Co substitution at the Fe sites, and higher Fe and Co content could be achieved by decreasing the Ti content to −Ti0.5. The ThMn12 structure with high Fe and Co content (i.e. low Ti content) was stabilized mainly by −Zr0.3 substitution at the Nd sites. The Zr substitution resolves the local mismatch in atomic size in the structure. Specifically, the atomic radius of Zr is about 88% that of Nd, so the local structure surrounding Nd (2a site) shrinks as a result of the substitution and resolves the size mismatch in the three types of local Fe six-fold symmetric hexagons in the structure. The effect of the α-(Fe, Co) phase on Js was evaluated from the phase's volume fraction measurement of 7.7% (8.1wt%) by electron backscatter diffraction. Nitrogenation of the starting alloy also resulted in augmentation of the c-axis magnetocrystalline anisotropy. Finally, we confirmed a high Js(−N1.3) of 1.71T (=1.67T, −0.04T for the α-(Fe, Co) phase) and Ha of 2.9–5.25MA/m (Ha(−N1.3)=5.25MA/m) in the (Nd0.7Zr0.3)(Fe0.75Co0.25)11.5Ti0.5Nα (α=0.60–1.30) compounds.

Structural transformation and magnetic properties of Sm–Fe alloys with V doping

A systematical investigation was carried out on structure and magnetic properties in SmFe9−x V x (x = 0.4, 0.8, 1.2) compounds prepared by a single-roller quenching method. The high cool-down rate leads to metastable TbCu7 phase in the parent compound, which gradually transforms into equilibrium ThMn12 structure with V-doping content increasing. The Curie temperature increases from 470 to 590 K with V doping, which is consistent with the phase transformation. Surprisingly, simultaneous increase in both coercivity and remanence is resulted by V doping, reaching the highest value of 685 kA·m−1 and 44.8 × 10−3 A·m2·g−1 in x = 1.2 compound, respectively. This phenomenon can be explained by the combination of phase transformation and intergranular exchange coupling through δM-H plots.

Targeted crystal growth of rare Earth intermetallics with synergistic magnetic and electrical properties: structural complexity to simplicity.

The single-crystal growth of extended solids is an active area of solid-state chemistry driven by the discovery of new physical phenomena. Although many solid-state compounds have been discovered over the last several decades, single-crystal growth of these materials in particular enables the determination of physical properties with respect to crystallographic orientation and the determination of properties without possible secondary inclusions. The synthesis and discovery of new classes of materials is necessary to drive the science forward, in particular materials properties such as superconductivity, magnetism, thermoelectrics, and magnetocalorics. Our research is focused on structural characterization and determination of physical properties of intermetallics, culminating in an understanding of the structure-property relationships of single-crystalline phases. We have prepared and studied compounds with layered motifs, three-dimensional magnetic compounds exhibiting anisotropic magnetic and transport behavior, and complex crystal structures leading to intrinsically low lattice thermal conductivity. In this Account, we present the structural characteristics and properties that are important for understanding the magnetic properties of rare earth transition metal intermetallics grown with group 13 and 14 metals. We present phases adopting the HoCoGa5 structure type and the homologous series. We also discuss the insertion of transition metals into the cuboctahedra of the AuCu3 structure type, leading to the synthetic strategy of selecting binaries to relate to ternary intermetallics adopting the Y4PdGa12 structure type. We provide examples of compounds adopting the ThMn12, NaZn13, SmZn11, CeCr2Al20, Ho6Mo4Al43, CeRu2Al10, and CeRu4Al16-x structure types grown with main-group-rich self-flux methods. We also discuss the phase stability of three related crystal structures containing atoms in similar chemical environments: ThMn12, CaCr2Al10, and YbFe2Al10. In addition to dimensionality and chemical environment, complexity is also important in materials design. From relatively common and well-studied intermetallic structure types, we present our motivation to work with complex stannides adopting the Dy117Co57Sn112 structure type for thermoelectric applications and describe a strategy for the design of new magnetic intermetallics with low lattice thermal conductivity. Our quest to grow single crystals of rare-earth-rich complex stannides possessing low lattice thermal conductivity led us to discover the new structure type Ln30Ru4+xSn31-y (Ln = Gd, Dy), thus allowing the correlation of primitive volumes with lattice thermal conductivities. We highlight the observation that Ln30Ru4+xSn31-y gives rise to highly anisotropic magnetic and transport behavior, which is unexpected, illustrating the need to measure properties on single crystals.

High Curie temperature of Ce–Fe–Si compounds with ThMn12 structure

We report the discovery of ternary CeFe12−xSix compounds possessing the ThMn12 structure. The samples were prepared by melt spinning followed by annealing. In contrast to other known Ce–Fe-based binary and ternary compounds, CeFe12−xSix compounds exhibit exceptionally high Curie temperatures whose values increase with added Si substitution. The highest Tc = 583 K in CeFe10Si2 rivals that of the well-established Nd2Fe14B compound. We ascribe the Tc behavior to a combination of Si-induced 3d band structure changes and partial Ce3+ stabilization.

NdFe12Nx hard-magnetic compound with high magnetization and anisotropy field

The NdFe12Nx compound with a ThMn12 structure (space group I4/mmm) was successfully synthesized by nitriding an NdFe12 layer grown on a W underlayer on a single-crystalline MgO(001) substrate. The c-axis expanded from 0.480 to 0.492 nm while the a-axis showed a slight contraction from 0.852 to 0.849 nm after the nitriding. Excellent intrinsic hard magnetic properties of μ0Ms ≈ 1.66 ± 0.08 T, μ0Ha ≈ 8 T, and Tc ≈ 550 °C, which are superior to those of Nd2Fe14B, were obtained.

Magnetic properties of CeFe11−xCoxTi with ThMn12 structure

A series of novel alloys CeFe11−xCoxTi (0 ≤ x ≤ 11) with ThMn12 structure has been successfully prepared by melt-spinning. The Curie temperature Tc increases with Co content x, reaching a maximum of 689 °C at x = 9 and declining to 664 °C at complete Co filling (x = 11). The room temperature saturation magnetization 4πMs and magnetocrystalline anisotropy Ha have been estimated by fitting the first quadrant demagnetization curve with the Stoner-Wohlfarth model. 4πMs first increases with increasing Co up to x = 3, then decrease. Ha has a complex dependence on Co content, which is indicative of a change in the easy magnetization direction from axis to plane and back as the Co content increases.

Effects of Gd substitution on the metamagnetic transition of NdCo9.5V2.5

Crystal structure and magnetic properties of the Nd1−xGdxCo9.5V2.5 compounds (x=0–1) have been investigated. The compounds crystallize in the tetragonal ThMn12 structure with space group I4/mmm. The lattice parameters a, c and the unit cell volume V decrease with the increase of Gd content. The Curie temperature of Nd1−xGdxCo9.5V2.5 increases monotonically upon the substitution of Gd for Nd. The critical field HCritL required to induce the magnetization jump decreases with increasing Gd content. The metamagnetic transition phenomenon becomes less obvious and even disappears with the substitution of Gd for Nd. The HCritH required for the metamagnetic transition increased with increasing Gd content at low substitution content. The saturation moment MS of the compounds decreases first then increases with the increased Gd content.

X-ray photoelectron spectroscopy and magnetic properties of CeCo7Mn5 and CeCo8Mn4 isostructural ThMn12 type compounds

The magnetic properties of CeCo7Mn5 and CeCo8Mn4 compounds have been investigated by combining X-ray photoelectron spectroscopy (XPS) and magnetic measurements in a wide temperature range (4–550) K and magnetic field up to 12 T. X-ray powder diffraction (XRD) measurements showed that CeCo7Mn5 and CeCo8Mn4 compounds are isostructural and crystallize in the ThMn12 structure type. XPS spectra pointed out the intermediate valence state of Ce atoms and that both Co and Mn atoms carry magnetic moments. The complex magnetic structure of CeCo7Mn5 and CeCo8Mn4 is determined by the competition between the ferromagnetic (Co–Co pairs) and antiferromagnetic (Co–Mn and Mn–Mn pairs) interactions. Two different ordering temperatures TN and TC correlated to antiferromagnetic and ferromagnetic coupling of 3d magnetic moments, respectively, are evidenced. Magnetic moments of about 1.6 μB/Co and 3.2 μB/Mn atoms were determined by correlating the magnetic data of the two compounds, in good agreement with the exchange splitting of XPS Co 3s and Mn 3s core levels.

Synthesis, Structure, and Magnetic and Electrical Properties of Yb(Mn,M)xAl12–x (M = Fe, Ru; x ≤ 2.5) Phases

Single crystals of Yb(Mn,M)xAl12–x (M = Fe, Ru; x ≤ 2.5) were grown utilizing an aluminum self-flux. Products crystallized in three structure types, the ThMn12 structure type, and two structural derivatives, the CaCr2Al10 structure type and the YbFe2Al10 structure type, depending on the starting amount of Mn relative to M. We outline the synthetic parameters used to obtain products in all three structure types and specifically address how stabilizing products in one structure type over another is a function of Mn:M reaction ratios. All compounds are structurally characterized with single crystal X-ray diffraction, and Yb(Mn,Fe)xAl12–x compounds are additionally characterized with temperature-dependent magnetic susceptibility and resistivity measurements. Yb(Mn,Fe)xAl12–x compounds exhibit paramagnetic behavior down to 2 K, as well as metallic resistivity down to ∼50 K. Below 50 K, Yb(Mn,Fe)xAl12–x compounds exhibit upturns in resistivity that indicate the onset of Kondo interactions.

Magnetic Properties of a HoFe<sub>5</sub>Al<sub>7</sub> Single Crystal

A single crystal of HoFe5Al7 (tetragonal ThMn12 structure) has been studied. HoFe5Al7 orders ferrimagnetically at TC = 227 K and has a compensation of the Ho and Fe sublattices at Tcomp = 65 K. The compound exhibits high easy-plane anisotropy. Strong anisotropy is also present within the basal plane, with the [110] axis being the easy magnetization direction. A high coercivity with Hc values attaining 1.6 T is found at 2 K. In the temperature range 40-80 K, HoFe5Al7 displays a field-induced magnetic transition along the easy [110] direction. Temperature dependence of the critical field Hcr of the transition is very strong, Hcr exceeds 14 T below 40 K.

Solid state phase equilibria and intermetallic compounds of the Al–Cr–Ho system

The solid state phase equilibria of the Al–Cr–Ho ternary system at 500°C were experimentally investigated. The phase relations at 500°C are governed by 14 three-phase regions, 29 two-phase regions and 15 single-phase regions. The existences of 10 binary compounds and 2 ternary phases have been confirmed. Al11Cr2, Al11Cr4 and Al17Ho2 were not found at 500°C. Crystal structures of Al9Cr4 and Al8Cr4Ho were determined by the Rietveld X-ray powder data refinement. Al9Cr4 was found to exhibit cubic structure with space group I4̄3m (no. 217) and lattice parameters a=0.9107(5)nm. Al8Cr4Ho crystallizes in ThMn12 structure type with space group I4/mmm (no. 139) and lattice parameters a=0.8909(4)nm, c=0.5120(5)nm. It is concluded that the obtained Al4Cr phase in this work should be μ-Al4Cr by comparing with XRD pattern of the hexagonal μ-Al4Mn compound.

Crystal growth and magnetic properties of Ln-Mn-Al (Ln=Gd, Yb) compounds of the CaCr2Al10 and ThMn12 structure types

We report the growth and characterization of LnMn2+xAl10−x (Ln=Gd, Yb) crystals adopting the CaCr2Al10 and ThMn12 structure types. Single crystals of LnMn2+xAl10−x were synthesized via the self-flux method and characterized with single crystal X-ray diffraction. We compare LnMn2+xAl10−x compounds adopting the CaCr2Al10 and ThMn12 structure types, and outline synthesis methods to obtain each polymorph. Magnetic susceptibility measurements show paramagnetic behavior down to 3K for both CaCr2Al10- and ThMn12-type compounds, with observed magnetic moments of 1.3μB for compounds adopting the CaCr2Al10 structure type to 4.2μB for those adopting the ThMn12 structure type. Compounds of both structure type exhibit metallic resistivity, with upturns at low temperature attributed to Kondo scattering.

Magnetic properties of Sm–Fe–Ti nanocomposite magnets with a ThMn12 structure

Sm–Fe–Ti alloys were produced by melt-spinning followed by heat treatment. The rapidly solidified melt-spun ribbons did not contain any hard magnetic ThMn12 phase and thus showed low coercivity. Although no hard magnetic ThMn12 phase was obtained by annealing SmFe12 melt-spun ribbon, annealed SmFe11.5Ti0.5 and SmFe11Ti melt-spun ribbons contained some hard magnetic ThMn12 phase and exhibited high coercivity. The highest coercivity of 0.4MA/m with a remanence of 63.5Am2/kg was achieved in the annealed SmFe11Ti melt-spun ribbon with the soft magnetic α-Fe and hard magnetic ThMn12 phases. The origin of the high coercivity in the annealed SmFe11Ti melt-spun ribbon was found to be the nanosized grains of the α-Fe and ThMn12 phases.

Magnetic Properties of RFe<sub>9</sub>Ti Single Crystals with ThMn<sub>12</sub> Structure

A comparative analysis of the magnetic properties of RFe11Ti and RFe9Ti single crystals (R=Ho,Er) with ThMn12 structure was carried out. It is shown that the decrease of iron content causes a 10% decrease in the saturation magnetization and a reduction by 10-15K in the Curie temperature. Besides, field induced spin reorientation appears at about 60 kOe in RFe9Ti, while in HoFe9Ti the First Order Magnetization Process transition field increases by 10 kOe with respect to the corresponding RFe11Ti compound.

Structural and magnetic properties of R3F29−xTix alloys and R3Fe33−xTi3 single crystals, [formula omitted],Gd,Tb,Dy,Ho,Er

In ternary R3Fe33-xTi3(x=0,1,…,7,R=Gd,Y) and R3Fe33-xTi3(R=Tb,Ho,Dy,Er,x=0,3,6,9) alloys, the anomalous wide homogeneous region of ThMn12 structure has been obtained. The single-crystal samples for each composition R3Fe33−xTi3 were prepared. By means of thermomagnetic analysis, it is shown that the TC of these single crystals monotonically decreases with the decrease in Fe concentration. With the decrease of iron concentration, the magnitude of magnetization saturation steadily decreases too. On the other hand, the temperatures of spin reorientation phases transition TSR for R=Tb,Ho,Dy,Er increase. From this, it follows that by the small changes in the Fe concentration it is possible to make a significant change of parameters of exchange interaction between R and 3d sublattices.

X-ray magnetic circular dichroism study of the RMn12−xFex series with R = Y, Er and Lu

The RMn12−xFex series of compounds of ThMn12 structure type exhibit rather complicated and composition sensitive magnetic properties. In a recent past, systematic neutron diffraction and magnetisation experiments allow to relate the main aspects of the magnetic structures to the polarisation state of the d-band. X-ray magnetic circular dichroism (XMCD) analyses have been undertaken on iron rich compounds with R = Y, Er, and Lu, thus probing the L2,3 edges of Mn and Fe as well as Er, and the M4,5 edges of Er. These experiments permit to better understand the local magnetic polarisation of the different interacting orbitals versus temperature and applied field as well as to precise the nature of the magnetic couplings acting between the 3d metals (M).

Crystal structure and electrical resistivity of the ScMnxAl12−x (4.0≤x≤4.6) compound

A new ternary ScMnxAl12−x (4.0≤x≤4.6) compound has been synthesized and its crystal structure has been investigated. It belongs to the ThMn12 structure type, space group I4/mmm. The lattice parameters vary non-linearly within its homogeneity region from a=0.87734(3), c=0.50629(2)nm for x=4.0 to a=0.87429(2), c=0.50467(2)nm for x=4.6. The temperature dependence of the resistivity of ScMn4.2Al7.8 and ScMn4.6Al7.4 alloys have been studied within the temperature range of 4.2–300K. Hopping conductivity in terms of variable range hopping is deduced over a significant temperature range (4.2–50K) from the behavior of ρ(T) according to 1/ρ=σ(T)=σ0exp(−A/T1/4). The width of the hopping conductivity regime is associated with the atomic disorder in the crystal structure. The present and earlier data indicate that Mn in the RMnxAl12−x ternaries is primarily responsible for the unusual transport observed.