Magnetic Properties of RB66 (R = Gd, Tb, Ho, Er, and Lu)

We report magnetic susceptibility measurements of RB₆₆ (R = Gd, Tb, Ho, Er, and Lu) boron-rich rare earth containing borides down to 50?mK. The data suggest a spin glass low temperature state for RB₆₆ (R = Gd, Tb, Ho, and Er) with the freezing temperatures below 1?K. The magnetic properties appear to be influenced by the anisotropy of the magnetic moments, probably via the crystalline electric field effects.     

Hydrogenation and Anisotropic Expansions in R3Fe29-xTx (R = Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

1.IntroductionIntensiveinvestigatiOnsontheR-Fe-T(R=rareearth,T=transitionmetalasastabilizingelement)phasediagrams,locatedattheironrichcorner,ledtothediscoveryofthenovelR2(Fe,T)l9phase[1l2]duetothegreatinterestinhighperfOrmanceper-manentmagneticmaterials.ItsrealstoichiometriccompOsitionandcrystallographicstructurewerede-terminedasaNd3(Fe,Ti)29-typestructurewithmon-oclinicsymmetry[3]andtheA2/mspacegrOup[4]byX-rnypowderdiffractiOn(XRD)andthenthiswasconfirmedbyneutrOnpOwderdiffraction[5'6…     

Reactions of hydrogen with R3Ni8Al intermetallides (R = Y,Pr, Nd,Gd, Tb,Dy, Ho,Er) with the Ce3Co8Si type of structure

Summary X-ray phase analysis, DTA, and volumetry have been applied to the reactions with hydrogen shown by R₃Ni₈Al compounds with structures of Ce₃Co₈Si type, where R = Y, Pr, Nd, Gd, Tb, Dy, Ho and Er. The R₃Ni₈Al react with hydrogen at room temperature and pressures below 0.1 MPa. Hydrides of composition R₃Ni₈AlH_x are obtained, where x=9.3 for Y, 10.3 for Pr, 11.4 for Nd, 8.7 for Gd, 6.9 for Tb, 5.7 for Dy, 5.4 for Ho, and 2.7 for Er. Hydride formation is accompanied by an increase in unit-cell volume by 5.7–18.2% without change in the initial hexagonal symmetry. Most of the hydrides decompose on heating at moderate temperatures up to 470 K. The main interest among these hydrides is in the Y₃Ni₅AlH_8.3, which can be recommended as a low-pressure hydrogen absorber.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 3, pp. 37–44, May–June, 1992.     

Crystal structure and optical properties of oxynitride rare-earth tantalates RTa-(O, N) (R = Nd, Gd, Y)

X-ray absorption and photoluminescence were used to investigate the structure of rare-earth tantalum oxynitrides RTa-(O, N) (R = Nd, Gd, Y). Owing to the size of the rare-earth element, the crystal structure tends towards the pyrochlore or defect fluorite-type structure. EXAFS suggested neodymium and yttrium atoms are coordinated either by 6 + 2 or 6 oxygen/nitrogen atoms in the Nd or Y respective oxynitrides although the coordination number of tantalum is six in both compounds. Photoluminescence for 5 at.% doped europium showed the spectra compatible with the point symmetry C_3v lower than O_h in fluorite and D_3d in pyrochlore structure type for both the Gd and Y tantalum oxynitrides. These measurements supported that their structure types were basically pyrochlore for Nd and Gd tantalum oxynitrides and defect fluorite for Y tantalum oxynitride but they are highly defective.     

New Ru-Based Layered Cuprates with 1232 Structure in the RuSr2(LnCe2−x Sr x )Cu2O z (Ln = Sm, Eu, and Gd) System

New Ru-based layered cuprates with 1232 structure have been synthesized in the RuSr₂(LnCe_2?x Sr _x )Cu₂O _z (Ln = Sm, Eu, and Gd) system. Nearly single-phase samples are obtained in the composition range from x = 0.0 to 0.2 for Ln = Sm and Eu, and at the composition of x = 0.2 for Ln = Gd. Each of the samples of Ln = Sm, Eu, and Gd with x = 0.2 crystallizes in a tetragonal lattice and lattice parameters a and c are 0.3845 and 1.700 nm, 0.3842 and 1.699 nm, and then 0.3839 and 1.698 nm, respectively. Each of them shows some anomalies at a low temperature in addition to a semiconductor-like temperature dependence of the resistivity. Especially, the sample with Ln = Gd shows two resistivity dropping phenomena at about 16 and 22 K. Then, all of nearly single-phase samples show diamagnetic signals originating from superconductivity, and also rapid increase of magnetization due to a transition from paramagnetic state to ferromagnetic one below 80 K.     

Structure and Magnetic Properties of La0.66Sr0.33MnO3 Thin Films Derived Using Sol-Gel Technique

In this paper the results of a study of the structural and magnetic properties of La_0.66Sr_0.33MnO₃ (LSMO) polycrystalline films grown on glass substrate using Sol-Gel technique are presented. The samples were structurally characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The average grain size range of 30 nm has been obtained from XRD investigations of granular LSMO samples. Zero Field Cooling (ZFC) and Field Cooling (FC) magnetization measurements have been performed and magnetic hysteresis loops of LSMO were recorded at various temperatures. The temperature dependences of the magnetization of LSMO films recorded in ZFC and FC regimes exhibited considerable difference between the curves. The blocking and the ferromagnetic phase transition temperatures of about 262?K and 300?K, respectively, were observed from magnetization measurements.     

Influence of Temperature on the Mutual Solubility of Components in the Binary Systems Tetradecane—Rare-Earth Metal (Nd,Sm, Gd,Y, Lu) Nitrate Solvate with TBP

The phase diagrams of binary liquid systems tetradecane—rare-earth metal (Nd, Sm, Gd, Y, Lu) nitrate solvate with TBP were studied in the temperature range 273.15–373.15 K. These diagrams contain the fields of homogeneous solutions and the field of separation into two liquid phases (I, II). Phases I and II are enriched, respectively, in tetradecane and Ln(NO₃)₃(TBP)₃ (Ln = Nd, Sm, Gd, Y, and Lu). With increasing temperature, the fields of separation into two liquid phases contract. The upper critical solution temperatures are dependent on the kind of rare-earth metal(III).     

Magnetic and magnetotransport properties of single-crystalline R_2PdGe_6(R = Pr,Gd and Tb)

Single crystals of R_2PdGe_6(R = Pr, Gd and Tb) compounds were grown by the Bi-flux method. Pr_2PdGe_6 is an antiferromagnetic compound with Néel temperature T_N= 15 K, in which a field-induced magnetic transition(spin flip) occurs when a magnetic field is applied along either a or b axis; a small magnetization and hysteresis loop were observed when a field is applied along c axis. Gd_2PdGe_6 is a collinear antiferromagnetic compound with T_N= 37 K along b axis. Tb_2PdGe_6 is an antiferromagnetic compound with T_N= 48 K and its hard magnetization direction is along b axis. The temperature dependences of the resistance of the entire three compounds present inflection points at the respective T_N. A large resistance(as well as magnetoresistance) change can be found at the spin flip transition of Pr_2PdGe_6, but the change is not obvious at the spin flop transition of Gd_2PdGe_6.     

Effect of Nickel Doping on the Magnetotransport Properties of?Sm0.55Sr0.45MnO3 Manganites

We studied the effects of nickel (Ni) doping on the magneto-transport properties of Sm_0.55Sr_0.45MnO₃ manganites near the metal-insulator transition. Various concentrations of Ni-doped Sm_0.55Sr_0.45MnO₃ samples up to 10% were prepared (Ni was partially substituted at the Mn-site). The temperature dependence of resistivity and magnetoresistance were measured as a function of Ni concentrations at various applied magnetic fields. We observed a nonlinear reduction of the metal-insulator transition temperature (MIT) with increasing concentration of Ni, 5% of Ni was sufficient to completely suppress the insulator-metal transition. Moreover, we observed dramatic increases of the resistance of the doped material with an increasing Ni-doping (5% of Ni increases R by more than 1000 times). The resistivity peaks at various magnetic fields collapses on themselves at the high temperature ends above the MIT. We also performed magnetization versus temperature measurements on both Ni-free the Ni-doped samples for FC and ZFC states. The FC and ZFC curves rapidly decrease to paramagnetic state at 175 K and 130 K for ZFC and FC states, respectively. For other Ni-doped samples, we observed a reduction in the paramagnetic transition temperature with increasing Ni concentration.     

New Ru-Based Layered Cuprates with 1232 Structure in the RuSr2(LnCe2?xSrx)Cu2Oz (Ln = Sm, Eu, and Gd) System

New Ru-based layered cuprates with 1232 structure have been synthesized in the RuSr₂(LnCe_2–x Sr _x )Cu₂O _z (Ln = Sm, Eu, and Gd) system. Nearly single-phase samples are obtained in the composition range from x = 0.0 to 0.2 for Ln = Sm and Eu, and at the composition of x = 0.2 for Ln = Gd. Each of the samples of Ln = Sm, Eu, and Gd with x = 0.2 crystallizes in a tetragonal lattice and lattice parameters a and c are 0.3845 and 1.700 nm, 0.3842 and 1.699 nm, and then 0.3839 and 1.698 nm, respectively. Each of them shows some anomalies at a low temperature in addition to a semiconductor-like temperature dependence of the resistivity. Especially, the sample with Ln = Gd shows two resistivity dropping phenomena at about 16 and 22 K. Then, all of nearly single-phase samples show diamagnetic signals originating from superconductivity, and also rapid increase of magnetization due to a transition from paramagnetic state to ferromagnetic one below 80 K.     

Preparation and some properties of rare earth iron borates,RFe3 (BO3)4

A new series of rare earth iron borates having the general formula RFe₃(BO₃)₄ (R=Y, Nd, Sm, Gd, Dy or Ho) was synthesized. The compounds were isostructural with huntite, CaMg₃(CO₃)₄, like other rare earth double borates, RM₃(BO₃)₄, M=A1 or Ga. Single crystals of Y and Gd compounds were grown by the flux method. Thermomagnetic measurements indicated that all the compounds are paramagnetic and have no spontaneous magnetization between 78°K and 730°K.     

Synthesis,order-disorder transition and magnetic properties of LiLnS2, LiLnSe2, NaLnS2 and NaLnSe2 (Ln=Lanthanides)

Ternary chalcogenides LiLnS₂, LiLnSe₂, NaLnS₂, and NaLnSe₂ (Ln-La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, Er, or Y) were prepared by heating the mixtures of elements. DTA(differential thermal analysis) measurements showed the first order transitions at high temperatures above 600 °C in LiLnS₂ (Ln=Dy, Ho, Er, Y), LiLnSe₂ (Ln=Gd to Er), NaNdS₂, and NaCeSe₂, which are considered order-disorder transitions between a NaCl and an α-NaFeO₂ structure. This is consistent with X-ray diffraction measurements. Magnetic susceptibility measurements revealed that all the lanthanides ions are in trivalent state.     

Rare-earth (Nd, Sm, Eu, Gd and Y) enhanced CeO2 solid solution nanorods prepared by co-precipitation without surfactants

Rare-earth doped CeO₂ solid solution nanorods were successfully prepared via a simple co-precipitation method without surfactants at room temperature and pressure. The products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of the doping contents, pH values, aging times and the precipitation agents on the structure and morphology were investigated. We found that the yield and uniformity of the nanorods were significantly improved by doping with optimum contents of Nd, Sm, Eu, Gd or Y. The intrinsically anisotropic structure of the rare-earth hydroxides is the driving force for the growth of the nanorods. Raman spectra show a great increase in oxygen vacancy concentrations on the doped CeO₂ solid solutions compared with that of pure CeO₂.     

Preparation of polycrystalline samples of the EuLnCuS<Subscript>3</Subscript> (Ln = Gd,Lu) compounds

Polycrystalline samples of the EuLnCuS₃ (Ln = Gd, Lu) compounds have been synthesized at 1220 and 1370 K by reacting flowing H2_S and CS₂ with mixtures of micron- and nanometer-sized particles of rare-earth mixed oxides and cuprates. The mixtures have been prepared at 1270 K by the thermolysis of cocrystallized rare-earth and copper nitrates and aqueous metal nitrate solutions sprayed into a reactor.     

The Effect of Gd Concentration on the Physical and Magnetic Properties of Bi1.7Pb0.3-xGdxSr2Ca3Cu4O12+y Superconductors

Bi–Pb–Gd–Sr–Ca–Cu–O bulk samples with nominal composition Bi_1.7Pb _0.3-xGd_xSr₂Ca₃Cu₄O_12+y (x=0.01, 0.05, 0.075, 0.10) were prepared by the melt-quenching method. The effects of different Gd doping on the structure have been investigated by electrical resistance, scanning electron micrographs, XRD, magnetization and magnetic hysteresis loop measurements. The magnetization measurements have been carried out as a function of magnetic field for fields up to 5 kOe at temperatures well below the zero resistance temperatures of the annealed samples. It has been found that the high-T_c superconducting phase, (2 2 2 3), is formed in the sample A with concentration x = 0.01, annealed at 840°C for 120 h. However, with increasing Gd³⁺ doping for Pb²⁺ the (2 2 2 3) phase gradually transforms into the (2 2 1 2) phase. The magnitudes of magnetization and initial susceptibility, | M | and | dM/dH|, and the hysteresis loop areas decrease with increasing Gd concentration x and/or temperature T. The fast decreases in | M|, | dM/dH |, and the hysteresis loop areas related to the superconducting volume, with increasing x and/or T seem to imply an existence of flux pinning centres in our samples. In order to support this implication the critical current densities J_c, of the samples, have been estimated at two fixed temperatures, 9 and 30 K. Our data have indicated that J_c decreases with increasing temperature and/or Gd concentration, as expected.     

Optical, magnetic and electronic properties of Ln2O2Te (Ln = La, Sm and Gd)

The synthesis, the optical and magnetic properties and the electronic structure of the rare-earth oxytellurides of formula Ln₂O₂Te (Ln = La, Sm and Gd) are reported. The magnetic measurements show that La₂O₂Te exhibit a diamagnetic behavior. The value of the magnetization M of Gd₂TeO₂ at our highest available field (50 kOe) is about 5.5μ_B, well below the expected value for two independent Gd ions (2gJ = 14μ_B) confirming the antiferromagnetic character of this compound. The magnetic properties of Sm₂TeO₂ reveal that Sm is in its 3+ oxidation state with a large Van Vleck contribution. The electronic structure calculations, studied by means of a first principles DFT approach, are consistent with the optical measurements and suggest an indirect band gap semiconductor behavior.     

Is the Two Dimensional Organic Conductor, τ-(EDO-S,S-DMEDT-TTF)2(AuCl2)1+y Clean or Dirty?

The transport properties of organic τ-type conductors seem to be very clean as well as very dirty depending on what we observe. To clarify this problem, we studied temperature and magnetic field dependence of resistivity, ρ(T, B), in τ-(EDO-S,S-DMEDT-TTF)₂(AuCl₂)_1+y. The properties that favor “probably dirty” are: i) stepwise ρ_a(T) increase below 20 K, which is suppressed by magnetic field, and ii) contrasted difference in ρ(T) as well as magnetization M(T) between field cooled (FC) and zero field cooled (ZFC). On the other hand, Shubnikov de Haas oscillations with very low Dingle temperature (T_D = 1.5 K) are typical of clean system. Based on these observations, we conclude this system changes from “dirty” to “clean” system by increase of magnetic field.     

Structural,magnetic and electronic transport studies of RAgSn2 compounds (R = Y,Tb, Dy,Ho and Er) with Cu3Au-type

RAgSn₂ compounds, where R = Y, Tb, Dy, Ho and Er, were synthesized by arc-melting and subsequent annealing at 870 K. The formation of cubic phases with Cu₃Au-type structure (space group ${\textit{Pm}}{\overline{3}}{\textit{m}}$ ) was studied. Magnetic property measurements showed that in paramagnetic state, the compounds with magnetic rare-earth atoms are Curie–Weiss paramagnets and order antiferromagnetically at low temperatures. YAgSn₂ is a Pauli paramagnet in 100–300 K temperature range. The electrical properties of RAgSn₂ compounds were investigated by means of electrical resistivity and Seebeck coefficient measurements in 4·2–300 K temperature range. All investigated compounds exhibit metallic type of conductivity. Electronic structure calculations based on full potential linearized augmented plane wave (FLAPW) method is also carried out to probe the magnetic and electronic structures of RAgSn₂ compounds. Comparisons between experimental data and calculations are discussed.     

Synthesis of New Pb-Based 1222 Cuprates Containing Phosphorus, (Pb0.75P0.25)Sr2(RE2–x–y Ce x Sr y )Cu2O z (RE = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y)

New Pb-based 1222 cuprates containing phosphorus have been synthesized in the (Pb_0.75P_0.25)Sr₂- (RE_2–x–y Ce _x Sr _y )Cu₂O _z (RE = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. The almost-single phase samples are obtained for 0.5≤x≤1.0 and y=0.1 in the cases of RE = Nd, Dy, Ho, Er, Tm, Yb and Y, while for 0.3≤x≤1.0 and y=0.1 in the cases of RE = Sm, Eu and Gd. The samples crystallize in a tetragonal lattice, the lattice parameters a and c are decreasing with the decrease of the ionic radius of the RE element. Even after annealing under 143 atm O₂ atmosphere at 400 °C, almost all the samples with the common values x=0.5 and y=0.1 are semiconductors with a transport process followed by three-dimensional variable range hopping. However, the samples of RE = Sm, Eu and Gd, which are of almost single 1222 phase, even for x=0.3 and y=0.1, show superconductivity with the onsets at about 25 K, 20 K and 22 K, respectively. Through this study, we find very important procedure for discovery of new superconducting 1222 compound.     

Magnetic properties of RRh3B2(R=La,Ce, Nd,Gd) compounds

The¹¹Bnmr results on RRh₃B₂(R=La, Ce, Nd and Gd) are reported. For CeRh₃B₂, specific heat and electrical resistivity are reported. From a comparative study of the¹¹Bnmr Knight shifts and the spin lattice relaxation times of these compounds it is shown that in CeRh₃B₂, there is strong hybridization of 4f states with the conduction electrons. A local moment on Ce with admixture of 4f and 5d–6s orbitals is suggested.