Magnetocrystalline anisotropy and exchange interactions in the novel R3(Fe, V)29 compounds (R = Y, Nd, Sm)

A type of magnetocrystalline anisotropy and exchange interactions of the novel ternary R₃(Fe, V)₂₉ compounds (R = Y, Nd, Sm) have been investigated. The compounds are uniaxial ferromagnets with easy magnetization direction along the [ 0 1] axis of the monoclinic lattice at room temperature. The temperature variations of the magnetic moment and the first anisotropy constant for Y₃(Fe, V)₂₉ are presented. The first order magnetization process along the hard magnetization direction takes place for Sm₃(Fe, V)₂₉ at T < 120 K. A magnetic anomaly is detected in the temperature dependence of the a.c. susceptibility for Nd₃(Fe, V)₂₉ which can be related to a spin reorientation.     

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.     

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 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.     

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.     

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.     

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.     

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.     

Optical study of praseodymium dicarboxylate [Pr(H2O)]2[O2C(CH2)3CO2]3.4H2O

Praseodymium dicarboxylate, [Pr(H₂O)]₂[O₂C(CH₂)₃CO₂]₃.4H₂O]–glutarate, Pr[glut], is synthesized by hydrothermal techniques. The title compound crystallizes in the monoclinic space group C2/c (No. 15). The rare earth cation is coordinated by nine oxygen atoms, eight oxygen atoms from the carboxylate groups and one from the water molecule. The local symmetry of Pr site is low, C_s. The absorption spectra of Pr[glut] are recorded from the visible to the far IR domain at 300, 77 and 9 K. Under various Ar⁺ laser excitations no emission is detected from ³P₀ and ¹D₂ excited levels of Pr³⁺ ion. In the low temperature absorption spectra only one electronic line is recorded for ³H₄→³P₀ transition. It confirms a unique local environment for the rare earth ion in Pr[glut]. The utility of the ‘barycenter curves’ in the attribution of electronic lines is demonstrated. Energy level scheme of 36 Stark components is deduced from the absorption spectra. The parametric calculation was performed on the whole 4f² (Pr³⁺) configuration with the starting set of crystal field parameters obtained previously for the Eu³⁺ ion in the isostructural compound. Eight free ion and nine phenomenological crystal field parameters in C_2v symmetry reproduce quite well several electronic levels of Pr³⁺ ion experimentally observed in Pr[glut]. A good r.m.s. standard deviation of 14.8 cm⁻¹ is obtained.     

X-ray investigations of ternary R3Pd4Ge4 samples

Ternary R₃Pd₄Ge₄ samples (R=Nd, Eu, Er) were investigated by means of X-ray single crystal (four circle diffractometer Philips PW1100, MoK radiation) and powder diffraction (MX Labo diffractometer, CuK radiation). The Er₃Pd_3.68(1)Ge₄ compound belongs to the Gd₃Cu₄Ge₄ structure type, space group Immm, a=4.220(2) Å, b=6.843(2) Å, c=14.078(3) Å, R₁=0.0484 for 598 reflections with F_o>4σ(F_o) from X-ray single crystal diffraction data. No ternary R₃Pd₄Ge₄ compound when R is Nd or Eu was observed. The Nd and Eu containing samples appeared to be multiphase. Ternary phases observed in the Nd₃Pd₄Ge₄ and Eu₃Pd₄Ge₄ alloys and their crystallographic characteristics are the following: NdPd₂Ge₂, CeGa₂Al₂ structure type, space group I4/mmm, a=4.3010(2) Å, c=10.0633(2) Å (X-ray powder diffraction data); NdPd_0.6Ge_1.4, AlB₂ structure type, space group P6/mmm, a=4.2305(2) Å, c=4.1723(2) Å (X-ray powder diffraction data); Nd(Pd_0.464(1)Ge_0.536(1))₂, KHg₂ structure type, space group Imma, a=4.469(2) Å, b=7.214(2) Å, c=7.651(3) Å, R₁=0.0402 for 189 reflections with F_o>4σ(F_o) (X-ray single crystal diffraction data); Eu(Pd,Ge)₂, AlB₂ structure type, space group P6/mmm, a=4.311(2) Å, c=4.235(2) Å; EuPdGe, EuNiGe structure type, space group P2₁/c, and ternary compound with unknown structure (X-ray powder diffraction data).     

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.     

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 chemistry, magnetism and thermodynamic properties of R2Pd2In

We report on magnetisation, resistivity and specific heat measurements of R₂Pd₂In compounds synthesised with the nominal composition R₄₀Pd₄₁In₁₉ (R=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y). Magnetic and thermodynamic measurements reveal antiferromagnetic order below 32 K for this series except for Y, La, Yb and Lu. An appreciably wide homogeneity range is found for Ce₂Pd_2+xIn_1−x where ferro- or antiferromagnetic order or both occur with typical features of a Kondo lattice. Yb₂Pd₂In exhibits intermediate valent behaviour and no magnetic order could be detected down to 0.3 K.     

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.     

Destabilization of LiBH4 by (Ce, La)(Cl, F)3 for hydrogen storage

The mixtures of LiBH₄ with halides of Ce or La in a molar ratio of 3:1 were investigated to explore their hydrogen storage properties. The ball milling of LiBH₄ with chloride of Ce or La yielded Ce(BH₄)₃ and La(BH₄)₃, while fluoride of Ce or La did not react with LiBH₄ during extended ball milling at room temperature. The dehydrogenation temperatures of the ball-milled mixtures were reduced to 220-320 °C, which were much lower than that of pure LiBH₄. The diborane emission during hydrogen release was observed at a low level. The dehydrogenation temperature is found to be affected by the composition of rare earth halides, but less influenced by ball milling time. The endothermic dehydrogenation reactions produced lithium halides, hydrides and borides of the corresponding rare earth element. Moreover, the LiBH₄ + 1/3(Ce, La)(Cl, F)₃ showed partial reversibility through the formation of an unknown borohydride, allowing for a potential hydrogen storage system.     

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.     

Structure of the ternary phase Co3Al8Ga and formation of the gallium-containing decagonal phase d-Co(Al, Ga)3(m)

The structure of the ternary phase Co₃Al₈Ga, Pearson symbol oI96, space group Immm, a=12.0081(7) Å, b=7.5701(6) Å, c=15.394(1) Å is isotypic with Co₂NiAl₉. Powder diffraction data are reported for this ternary intermetallic compound. Using liquid quenching, the metastable pseudoternary decagonal phase d-Co(Al, Ga)₃(m) was obtained in the aluminium-rich portion of the ternary system Co–Al–Ga. Gallium substitutes for aluminium atoms in the d-Co(Al, Ga)₃(m) phase up to a mol fraction x_Ga=0.10. In the phase of the binary system Co–Al richest in aluminium, Co₂Al₉, the aluminium atomic positions can be occupied by gallium up to a gallium content of x_Ga=0.05.     

Phase formation in rapidly solidified R2T17 intermetallics

Rapid solidification was utilized to produce a series of light and heavy rare earth-transition metal intermetallics in the R_H–Co, R_L–Co/Fe, and Sm–Co(Fe) systems with R_H = Dy and Tb and R_L = Pr and Sm. The influence of Nb–C and Zr–C additions on phase formation in the binary and ternary alloys has also been investigated. The X-ray diffraction patterns obtained with synchrotron radiation were refined by the Rietveld method for structural phase determination and analysis. It was found that the ability to create disorder strongly depended on the rare earth element, with light rare earth systems possessing more disorder, and rapid solidification effectively suppressed the development of long-range order in these compounds. Cobalt in contrast to iron favored the formation of disordered structures. Replacement up to two out of the three of the cobalt atoms with iron in the Sm–Co–Fe system has retained the establishment of the disordered TbCu₇-variant and exhibited complete cobalt–iron solubility. Additions of Nb–C and Zr–C have also greatly influenced the order formation. The comparison of lattice parameters of the intermetallic compounds obtained by rapid solidification to the parameters of equilibrium 2–17 phases summarized in the literature revealed that formation of partially ordered and disordered structures was associated with expansion of the both a- and c-axes in Th₂Zn₁₇- and Th₂Ni₁₇-type phases for all binary compounds.     

The ternary system: H2O–Fe(NO3)3–Co(NO3)2 isotherms −15 and −25 °C

The binary system H₂O–Fe(NO₃)₃ has been investigated at temperature ranging between –25 and 47 °C.The solid–liquid equilibria of the ternary system H₂O–Fe(NO₃)₃–Co(NO₃)₂ were studied at −15 and −25 °C by using a synthetic method based on conductivity measurements which allows all the characteristic points of the isotherms to be determined, and the stable solid phases which appear are respectively: ice, Fe(NO₃)₃·9H₂O, Fe(NO₃)₃·6H₂O, Co(NO₃)₂·9H₂O, Co(NO₃)₂·6H₂O and Co(NO₃)₂·3H₂O.     

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

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