Peculiarities of the R3(Fe,Si)29 phase formation in the Sm---Fe---Si system

The phase content of the Sm(Fe_1−xSi_x)_y alloys (0.05≤x≤0.15; 8.5≤y≤12) has been studied by X-ray diffraction using micromonocrystals. The compounds Sm₂(Fe,Si)₁₇, Sm(Fe,Si)₁₂ and a novel Sm₃(Fe,Si)₂₉ compound with a monoclinic unit cell are found. The lattice parameters of Sm₃(Fe,Si)₂₉ are: a=1.056 nm, b=0.850 nm, c=0.966 nm, β=96.8°. This compound forms as a result of a solid state transformation from the high-temperature Sm₂(Fe,Si)₁₇ phase. Diffuse effects observed in rocking photographs suggest transition structures arising from this transformation. The Curie temperatures of Sm₃(Fe,Si)₂₉ vary in the interval 496–521 K.     

Magnetic properties of novel compounds R3(Fe,Cr)29Xy (R=Nd, Sm and X=N, C)

The novel ternary rare-earth iron-rich interstitial compounds R₃(Fe,Cr)₂₉X_y (R=Nd, Sm and X=N, C) with the monoclinic Nd₃(Fe,Ti)₂₉ structure have been successfully synthesized. Introduction of the interstitial nitrogen and carbon atoms led to a relative volume expansion ΔV/V of about 6% and an enhancement of Curie temperatures T_c about 268 K for the nitride and about 139 K for the carbide, respectively. The Nd₃Fe_24.5Cr_4.5X_y compounds have a planar anisotropy at room temperature. A first-order magnetization process (FOMP) with critical field B_cr=4.4 T and 3.1 T at room temperature were observed for the Nd-nitride and carbide compounds, respectively. The Sm₃Fe₂₄Cr₅X_y compounds were found to have a large uniaxial anisotropy of about 18 T at 4.2 K and about 11 T at 293 K. A FOMP with B_cr=2.3 T was also observed in the Sm-nitride compounds at 4.2 K. Magnets with coercivity of μ_OjH_c0.8 T at 293 K has been successfully developed from the Sm₃Fe₂₄Cr₅X_y (X---N and C) phases.     

Magnetic anisotropy and magnetic properties of RTSi (R=Gd, Y; T=Mn, Fe) compounds

Magnetic properties of Gd_xY_1−xMnSi and GdMn_xFe_1−xSi compounds with CeFeSi-type structure have been studied by magnetization measurements in the temperature range 77–600 K in static magnetic fields up to 12 kOe. The measurements for some compounds have been carried out on single crystal samples. The easy magnetization direction of all single crystal samples was found to be the c axis. The value of the anisotropy constant K₁ for GdMnSi was estimated to be 2.0·10⁶ erg cm⁻³ at 77 K. The substitution in both rare earth and 3d sublattices leads to a sharp increase in magnetic anisotropy of these compounds. The concentration dependencies of magnetic ordering temperatures, effective magnetic moments and paramagnetic Curie temperatures have been determined. The obtained results can be explained by the modification of the band structure due to the change of interatomic distances and the filling of 3d band.     

MAGNETIC PROPERTIES OF R 3(Fe, Mo) 29 N x (R=Sm OR Y) INTERSTITIAL NITRIDES

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Effect of interstitial hydrogen and nitrogen on the magnetocrystalline anisotropy of Y2Fe17

Magnetocrystalline anisotropy of Y₂Fe₁₇ and of its nitride and hydrides has been measured on magnetically oriented samples. The anisotropy is defined by the local site anisotropy behavior and in a first approximation depends mainly on the lattice expansion along the c axis.     

Magnetic structures of R2RhSi3 (R=Ho, Er) compounds

Powder X-ray and neutron diffraction and magnetic measurements have been performed on R₂RhSi₃ (R=Ho and Er) compounds at low temperatures. The compounds crystallize in a derivative of the hexagonal AlB₂-type structure. The crystal structure parameters have been refined on the basis of the X-ray and neutron diffraction patterns collected in the paramagnetic region. These compounds are antiferromagnets with Néel temperatures of 5.2 K for Ho₂RhSi₃ and 5 K for Er₂RhSi₃. Both compounds exhibit collinear magnetic structures, described by the propagation vector k=(1/2,0,0) for Ho₂RhSi₃ and k=(0,0,0) for Er₂RhSi₃. This magnetic order is stable in the temperature range between 1.5 K and the Néel temperature.     

Magnetocrystalline anisotropy of R2Fe17Hx (x=0, 3) single crystals

The magnetocrystalline anisotropy of R₂Fe₁₇ (R=Y, Gd, Tb, Ho and Er) and their hydrides are studied by analyzing the magnetization curves of single crystal samples in the temperature range 4.2–300 K in magnetic fields up to 140 kOe. There is no noticeable influence of hydrogenation on the magnetic anisotropy in the Y₂Fe₁₇ and Gd₂Fe₁₇ compounds. An easy-plane to easy-cone transition is detected for a Tb₂Fe₁₇H₃ single crystal after hydrogenation. A significant change of the magnetization process has been observed in the hydrides Ho₂Fe₁₇H₃ and Er₂Fe₁₇H₃. Hydrogenation induces a FOMP-type transition in the Ho₂Fe₁₇H₃ compound and, on the contrary, leads to the disappearance of the FOMP type transition in the Er₂Fe₁₇H₃ compound. The obtained results are discussed on the basis of a model based on the interaction of the quadrupolar moment and the magnetic moment of the 4f electron shell of the rare earth ion with the interstitial hydrogen. It is established that the orientation of the quadrupolar moment of the asymmetric 4f shell with respect to the direction of the resulting magnetic moment of 4f electrons plays an important role.     

Structural and magnetic properties of a novel compound with Y3(Fe, V)29 stoichiometry and disordered CaCu5-type structure

A novel phase with nominal composition Y₃Fe_27.5V_1.5 has been synthesized by arc melting elemental constituents, followed by annealing at 1123 K. The samples were analyzed by electron microprobe analysis and the stoichiometric composition was Y_3.04Fe_27.56V_1.44. X-ray diffraction from powder samples shows that the structure is of a disordered CaCu₅-type (Space Group: P6/mmm) with lattice parameters a=4.8769(1) Å, c=4.1729(3) Å. This disordered structure, revealed using standard difference Fourier methods, can be considered as a TbCu₇-type, containing iron dumbbell sites. The disorder is not restricted to the rare earth sites and the dumbbell atoms, but is observed at other sites as well. The stoichiometric formula derived by Rietveld analysis is Y_3.00(3)Fe_28.5(3). Magnetic measurements give a Curie temperature of 439(5) K, and a saturation magnetization of 156.4 and 125.5 A m² kg⁻¹ at 5 and 300 K, respectively. The anisotropy field is 4.76 T at 5 K and 2.43 T at 300 K. X-ray powder diffraction patterns of magnetically aligned powder samples indicate that the magnetocrystalline anisotropy is of easy plane type. This result is supported from the analysis of the magnetization measurements on aligned powders which give K₁<0, K₂>0 and K₁+2K₂<0, a result that confirms the easy plane anisotropy. Mössbauer spectra were also obtained and fitted with a model consistent with the disorder. The average hyperfine fields are 28.4 and 21.5 T at 4.2 and 300 K, respectively.     

Structural and magnetic properties of Nd3(Fe,Ti)29Cx carbide

Nd₃(Fe,Ti)₂₉C_x, carbide has been synthesized by gas-solid reaction. An enhancement of the Curie temperature T_c from 437 K to 575 K is observed, reflecting a lattice expansion of 4.1% upon carbonation. The room temperature saturation magnetization M_s of the carbide is 145.5 A m² kg ¹ and the average hyperfine field, H_eff, 24.8 T. The magnetic structure of Nd₃(Fe,Ti)₂₉C_x carbide changes from easy-cone-like in the case of the parent compound to axial-like after carbonation with a room temperature anisotropy field H_A of 8 T.     

New Zr6CoAs2-type R6MnSb2 and R6MnBi2 compounds (R=Y, Lu, Dy, Ho)

A powder X-ray diffraction investigation of the new ternary compounds Zr₆CoAs₂-type R₆MnSb₂ and R₆MnBi₂ (R=Y, Lu, Dy, Ho) is reported. The compounds Ho₆MnSb₂ (a=0.8070(2) nm, c=0.4230(1) nm), Lu₆MnSb₂ (a=0.7930(1) nm, c=0.4173(1) nm), Y₆MnBi₂ (a=0.8242(1) nm, c=0.4292(1) nm), Dy₆MnBi₂ (a=0.8211(1) nm, c=0.4286(1) nm), Ho₆MnBi₂ (a=0.8164(1) nm, c=0.4250(1) nm) and Lu₆MnBi₂ (a=0.8019(2) nm, c=0.4185(1) nm) crystallize in the hexagonal Zr₆CoAs₂-type structure (space group P6b2m No. 189). The Zr₆CoAs₂-type structure is a superstructure of the Fe₂P-type structure.     

Crystal structure of the R3Si1.25Se7 (R = Pr, Nd and Sm) compounds

The crystal structure of new ternary R₃Si_1.25Se₇ (R = Pr, Nd and Sm) compounds (Dy₃Ge_1.25S₇ structure type, Pearson symbol hP22.5, space group P6₃, a = 1.05268 (3) nm, c = 0.60396 (3) nm, R_I = 0.0897 for Pr₃Si_1.25Se₇; a = 1.04760 (3) nm, c = 0.60268 (3) nm, R_I = 0.0891 for Nd₃Si_1.25Se₇; a = 1.04166 (6) nm, c = 0.59828 (6) nm for Sm₃Si_1.25Se₇) was determined using X-ray powder diffraction. The nearest neighbours of the R and Si atoms are exclusively Se atoms. The latter form distorted trigonal prisms around the R atoms, octahedra around the Si1 atoms and tetrahedra around the Si2 atoms. Tetrahedral surrounding exists for Se1 and Se3 atoms. Six neighbours surround every Se2 atom.     

Structure and magnetic properties of Gd3(Fe1−xTix)29 (x=0.011–0.034)

Single-phase compounds Gd₃(Fe_1−xTi_x)₂₉ (x=0.0110.034) have been synthesized. Gd₃(Fe_1−xTi_x)₂₉ crystallises in a monoclinic lattice with space group P2₁/c, and the crystal structure is refined by the Rietveld technique based on X-ray powder diffraction data. Thermomagnetic analysis indicates that the Curie temperature of the compounds ranges from 517 K to 538 K. The saturation magnetizations of the Gd₃(Fe_1−xTi_x)₂₉ (x=0.011, 0.022, 0.034) at 1.5 K are 103.6, 102.0 and 94.3 Am²/kg, and the anisotropy fields at 1.5 K are 6.0, 6.2 and 6.4T, respectively.     

PREPARATION OF A SINGLE PHASE R 3(Fe, Mo) 29 (R=Ce, Nd, Sm, Gd, Tb, Dy AND Y)

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一维NiFe1.98RE0.02O4(RE=Pr, Nd, Sm)纳米丝的结构和磁性能

采用溶胶-凝胶法、静电纺丝技术和热处理技术相结合制备了一维NiFe_(1.98)RE_(0.02)O_4 (RE=Pr,Nd,Sm)纳米丝。利用X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FT-IR)、扫描电子显微镜(SEM)和振动样品磁强计(VSM)对NiFe_(1.98)RE_(0.02)O_4 (RE=Pr,Nd,Sm)纳米丝的结构、形貌和磁性能进行表征。结果表明,NiFe_(1.98)RE_(0.02)O_4(RE=Pr,Nd,Sm)纳米丝表面光滑、直径均匀、连续,直径约60nm。掺杂Pr~(3+),Nd~(3+),Sm~(3+)均没有改变NiFe204的尖晶石结构,掺杂均降低了NiFe_2O_4的结晶度,晶粒尺寸D从44.8nm减小到33.8nm。NiFe_(1.98)RE~(0.02)O_4 (RE=Pr,Nd,Sm)纳米丝都表现出软磁特性。NiFe_(1.98)RE_(0.02)O_4 (RE=Pr,Nd,Sm)纳米丝的饱和磁化强度(Ms)分别为39.58,41.10,34.23 A·m~2/kg;矫顽力(H_c)分别为14119.2, 13678.4,15937.6 A/m;其中NiFe_(1.98)Nd_(0.02)O_4纳米丝的M_s (41.10 A·m~2/kg)最大,矫顽力H_c(13678.4A/m)最小,软磁性能最好。     

Crystal structure of the Nd(Ru0.6Ge0.4)2 and ErRuGe compounds

Using X-ray powder and single crystal diffraction, the crystal structures of the Nd(Ru_0.6Ge_0.4)₂ and ErRuGe compounds were investigated. The compounds belong to the KHg₂ and TiNiSi type structure, respectively.     

On Synthesis and Magnetic Properties of Nd(Fe, Mo, Ti)12Zx (Z=N, H)

NdFe_10+xMo_2−2xTi_x compounds with 0≤x≤1.0 have been prepared by using the reduction–diffusion process with superfine precursors as starting materials. With increasing Ti-content, the intrinsic magnetic properties, such as the Curie temperature, saturation magnetization and magnetocrystalline field, are improved. The interstitial compounds NdFe_10+xMo_2−2xTi_xZ_y (Z=N, H) were obtained and exhibit significant enhancement of the intrinsic magnetic properties upon nitrogenation.     

R3（Fe,Mo）29（R=Sm,Y）化合物及其氮化物的磁性

合成了Ｒ３（Ｆｅ,Ｍｏ）２９（Ｒ＝Ｓｍ,Ｙ）化合物并在０．１ＭＰａ氮气条件下通过气相氮化法制备出其氮化物。Ｒ３（Ｆｅ,Ｍｏ）２９金属间化合物氮化后仍保持母相结构,但是晶胞体积发生膨胀,氮化处理同时导致化合物居里温度Ｔｃ和饱和磁化强度σｓ升高同时Ｓｍ３（Ｆｅ,Ｍｏ）２９化合物由平面各向异性变为单轴各向异性,但Ｙ３（Ｆｅ,Ｍｏ）２９Ｎｘ化合物的各向异性仍与母相相同,为面各向异性。     

Structural investigation of ternary RIr3B2 compounds (R=Ce and Pr)

Structural studies were performed for the ternary RIr₃B₂ compounds (R=Ce and Pr) from as cast samples. The crystal structure of the ternary boride CeIr₃B₂ (CeCo₃B₂ structure type, space group P6/mmm, a=5.520(3) Å, c=3.066(2) Å, Z=1, V=80.91 ų, ρ_x=15.154 g cm⁻³) was refined to R₁=0.0470, wR₂=0.1240 from single-crystal X-ray diffraction data. The new ternary boride PrIr₃B₂ was found to be isostructural with the CeIr₃B₂ compound. Its lattice parameters a=5.5105(2) Å, c=3.1031(1) Å were obtained from a Rietveld refinement of X-ray powder diffraction data.     

The crystal structure of the novel ternary silicide Sm4Pd4Si3

The crystal structure of the compound Sm₄Pd₄Si₃ was determined by the single-crystal method (KM-4 automatic diffractometer, Mo K radiation. Sm₄Pd₄Si₄ has the monoclinic Nd₄Rh₄Ge, type structure: space C2/c, mC44 (No. 15). a = 20.693(6), B = 5.584(1), C = 7.699(2) Å, β = 109.48(3)°, V = 838 Å, Z = 4, μ - 36.23 mm¹, R =_F = 0.0537, R _F = 0.0435 for 1652 unique reflections. The coordination numbers of samarium atoms are 17 and 18. For palladium and silicon atoms icosahedra and trigonal prisms with additional atoms are typical as coordination polyhedra. The structure of Sm₄Pd₄Si₄ is composed of fragments of the YPd₂Si and Y₁Rh₂Si₂ structure in a ratio 1:1.     

Synthesis, photoluminescence, thermoluminescence and dosimetry properties of novel phosphor KSr4(BO3)3:Ce

Polycrystalline powder sample of KSr₄(BO₃)₃ was synthesized by high-temperature solid-state reaction. The influence of different rare earth dopants, i.e. Tb³⁺, Tm³⁺ and Ce³⁺, on thermoluminescence (TL) of KSr₄(BO₃)₃ phosphor was discussed. The TL, photoluminescence (PL) and some dosimetric properties of Ce³⁺-activated KSr₄(BO₃)₃ phosphor were studied. The effect of the concentration of Ce³⁺ on TL intensity was investigated and the result showed that the optimum Ce³⁺ concentration was 0.2 mol%. The TL kinetic parameters of KSr₄(BO₃)₃:0.002 Ce³⁺ phosphor were calculated by computer glow curve deconvolution (CGCD) method. Characteristic emission peaking at about 407 and 383 nm due to the 4f⁰5d¹ → ²F_{(5/2, 7/2)} transitions of Ce³⁺ ion were observed both in PL and three-dimensional (3D) TL spectra. The dose–response of KSr₄(BO₃)₃:0.002 Ce³⁺ to γ-ray was linear in the range from 1 to 1000 mGy. In addition, the decay of the TL intensity of KSr₄(BO₃)₃:0.002 Ce³⁺ was also investigated.