Single Crystals Of Nd Research Articles

Magnetic properties of monocrystalline Nd 2(Fe, Co, Ni) 14B

Single crystals of Nd 2(Fe 1− x−y Co x Ni y ) 14B were prepared in an IR-imaging furnace by applying the floating zone-melting technique. Their saturation magnetization and anisotropy field were measured over the temperature range 4.2–300 K. It has been found that double substitution of Co and Ni atoms for Fe atoms in the Nd 2Fe 14B compound restores the values of saturation magnetization and anisotropy field which are lost by single substitution of Ni atoms for Fe atoms. This phenomenon is understood by a model of ordered substitution of Co and Ni atoms in the iron sublattice.

Measurement of magnetic forces on small high Tc superconductor single crystals in magnetic field gradients

In this paper a brief account is given of a new instrument which allows quantitative measurements of magnetic forces in very small single crystals. The crucial element of the instrument is a capacitor with plane and parallel plates, one of which can be elastically displaced to change the distance between them. Forces in the range of 10 −9 N can be measured with this set-up. Good quality single crystals of Nd 1.85Ce 0.85CuO 4, placed in low magnetic field gradients, have been studied at different fields and temperatures. To prove the capability of the method for studying magnetic relaxation phenomena, results are presented of d M/dln t for this material at several low magnetic fields, H c1 < H < H ∗ (where H ∗ is the field for complete field penetration) at 4.2 K.

Critical current in single crystalline Nd 1.85Ce 0.15CuO 4 from AC susceptibility

We report measurements of the temperature dependence of the critical current in a single crystal of Nd 1.85Ce 0.15CuO 4. This dependence is deduced from the variation versus the AC magnetic field of the real part of the magnetic susceptibility at different temperatures. In the framework of the critical state model, we deduce the variation of the critical current from 4.5 K to 15 K.

Effects of Ce substitution and reduction on conduction in Nd 2- xCe xCuO 4 single crystals

Electrical resistivity and magnetoresistivity of as-grown and reduced single crystals of Nd 2- x Ce x CuO 4 have been investigated to elucidate the effects of the Ce substitution and the reduction on the electrical conduction. The resistivity of the as-grown Ce-substituted samples shows a minimum as a function of temperature, indicating electron localization in the low-temperature range. The Ce concentration dependence of the localization behavior demonstrates that the Ce ions increase the electron carriers and cause the random potential on the conduction plane as well. The reduced superconducting sample has no localization behavior and a larger temperature coefficient of resistivity than those of the reduced samples. The results strongly suggest that excess oxygen, which creates random potential as in the case of the Ce ions, exists in the as-grown samples and that the superconductivity is induced by the carrier increase and the removal of the random potential due to the reduction.

Magnetic order of Cu in Nd 2– xCe xCuO 4

The magnetic ordering in single crystals of Nd 2– x Ce x CuO 4 with x=0.0 to 0.22 has been studied by neutron diffraction measurements. Long-range antiferromagnetic order for Cu is observed for crystals with small Ce concentrations. Both the ordered moment for Cu and the Néel temperature decrease with increasing Ce concentration x. Two Cu spin reorientation transitions are also observed for crystals with small Ce concentrations. The temperature dependence of the ( 1 2 1 2 0) magnetic Bragg peak shows that these spin reorientation transitions are sharp for the pure sample, while they are not as sharp for the doped samples due to the randomness of the Ce. The fraction of the Cu spins which participate in the spin reorientations also decreases with increasing x. In Nd 2CuO 4, both spin reorientation transition temperatures increase with magnetic field at the rate of about 1.2 and 0.8 K/T, respectively.

Neutron diffraction study of the magnetic ordering of the Cu ++ spins in Nd1.5Ba1.5Cu3O6+x

Elastic neutron scattering experiments performed on single crystals of Nd 1.5 Ba 1.5 Cu 3 O 6+ y reveal successive antiferromagnetic (AF) ordering of the Cu ++ spins. The as grown single crystals show an AF structure characterized by a Neél temperature T N1 ∼ 390 K and a magnetic wave vector ( 1 2 1 2 0 ) referring to the tetragonal structure of NdBa 2 Cu 3 O 6. As the temperature is lowered below T N2 ∼150 K, a spin reorientation develops and a second AF ordering with ( 1 2 1 2 1 2 ) wave vector is stabilized. When the samples are oxygenated the tetragonsl symmetry and the Neél temperature T N1 remain unchanged, whereas the spin reorientation at T N2 is suppressed. The results indicate that the Nd Ba substitution increases the stability of the tetragonal structure upon the oxygen content. This may induce new possibilities of local oxygen ordering that favour the presence of holes in the deficient layer.

An upper limit on the lower critical field in single crystal Nd 1.85Ce 0.15CuO 4−y

Isothermal magnetization measurements have been carried out on a single crystal of Nd 1.85Ce 0.15CuO 4−y at several temperatures below T c for field directions both parallel and perpendicular to the basal ( ab) plane of the crystal. An upper limit on H c1 for both these orientations has been obtained from these measurements. A very large anisotropy of ∼40 is found between the two directions.

Ultrasound study on Nd 1.85Ce 0.15CuO 4−y single crystals

Ultrasonic experiments on superconducting and non-superconducting single crystals of Nd 1.85Ce 0.15CuO 4−y are reported. No anomalous behaviour of the sound velocity of the longitudinal mode C 33 and transverse mode C s generated in the basal plane has been observed at the superconducting transition in agreement with the thermodynamic prediction.

Crystal growth and physical properties of Nd 2−xCe xCuO 4−y single crystals

Single crystals of Nd 2−xCe xCuO 4−y with dimensions up to 5 × 8 × 0.15 mm 3 were grown from Cu 2O flux at 1250 °C. The effects of the reduction time at 900 °C in N 2 atmosphere have been investigated. For more than 20 hours we found by EDAX analysis an increase of Ce and Cu concentration at the crystal surface and we simultaneously observe, by means of X-ray diffraction, the appearance of a cubic phase (Nd 0.5Ce 0.5O 1.75) within the crystal. The best superconducting properties are obtained for a reduction at 900 °C for 10–15 hours with T c = 22.9 K and ΔT c = 0.4 K. The resistivity shows a metallic temperature dependence, ρ(300K) = 550μΩcm and the Hall coefficient (H//c-axis) is negative between T c and room temperature.

Raman study of superconducting Nd2−xCexCuO4−y single crystals

Abstract Polarized Raman spectra from superconducting (reduced) and non-superconducting (unreduced) single crystals of Nd 2− x Ce x CuO 4− y ( x =0.16) are presented. The spectra were measured at room temperature by the micro-Raman technique and with different exciting wavelengths. No differences between unreduced samples were detected. Four Raman modes with well characterized polarization properties are found. They are compound with the predictions of factor group analysis of the undoped compound. The A 1g mode at 229 cm -1 which corresponds to out-of-phase motions of the Nd 3+ ions shows a resonant behavior at about 2.4 eV that we ascribe to electric transitions among the 4f 3 electronic levels of the Nd 3+ ion. The modes at 333 (B 1g ) and 475 (E g ) cm -1 are assigned to motions of the oxygens which are not in CuO 2 planes. The strong feature at 585 cm -1 has a clear A 1 character and is interpreted as being due to an IR mode associated with the motion along the c -axis of the oxygens in the CuO 2 planes, which becomes Raman active by the presence of the Ce impurity.

Raman study of pure and Ce doped single crystals of Nd 2− xCexCuO 4− y

We present the polarized Raman spectra from single crystals of Nd 2CuO 4− y obtained at room temperature and by micro-Raman technique. Three of the four Raman active phonons predicted by factor-group analysis are found at 229 (A 1g ), 330 (B 1g ), 488 (E g) cm − 1 and attributed to the certain lattice vibrations. The Raman forbidden band around 580 cm − 1 probably induced by oxygen vacancies is also observed. The oxygen E g mode at 488 cm − 1 and the band at 580 cm − 1 are seen to be sensitive to oxygen deficiency. In contrast to the Sr doped La 2 CuO 4 , the doping with Ce supresses the intensity of the A 1g (Nd) peak at 229 cm − 1 .

Absorption spectrum of Nd 3+:LiNH 4SO 4 single crystals

Light pink single crystals of Nd(III):LiNH 4SO 4 have been grown under the slow evaporation method. The absorption spectrum of Nd(III) crystal has been recorded in the UV-VIS and N1R regions. The energies and intensities of thirteen levels have been measured. By applying a least-squares fit analysis and Judd-Ofelt parametric procedures, a good fit between the experimental and theoretical energies and intensities for the Nd(III) ion has been obtained. Based on the magnitude of the bonding parameter for the ion studied, the bonding in the crystal lattice is suggested to be covalent. The evaluated spectroscopic parameters relating to the ion are reported.

Experimental and theoretical investigations of the magnetic susceptibility and anisotropy of Nd(OH)3.

Measurements are reported on the magnetic susceptibilities and anisotropies of single crystals of Nd(OH${)}_{3}$ in the temperature range between 300 and 77 K. The intermediate-coupling scheme with J mixing under the crystal field of ${C}_{3h}$ symmetry is used to obtain the crystal-field energy levels and their eigenfunctions. Matrix elements of the Coulomb, spin-orbit, and crystal-field interactions within the ${f}^{3}$ configuration are calculated. The g values are found to be ${g}_{?}$=3.65\ifmmode\pm\else\textpm\fi{}0.01 and ${g}_{\ensuremath{\perp}}$=1.95\ifmmode\pm\else\textpm\fi{}0.01 in close agreement with the experimental values quoted by P. D. Scott (Ph.D. dissertation, Yale University, 1970). The calculated crystal-field splitting explains successfully the temperature dependence of the specific heat as observed by Chirico and Westrum [J. Chem. Thermodyn. 12, 311 (1980)] in the temperature range between 350 and 20 K. Saturated magnetizations parallel and perpendicular to the applied magnetic field are found to be 271 and 145 emu/${\mathrm{cm}}^{3}$, respectively.

A high resolution neutron scattering study of single crystal neodymium

It is well known that neodymium develops a modulated antiferromagnetic structure below a first-order transition at T N = 19.9 K. In marked contrast to the other lanthanide metals, no well-defined magnetic excitations have previously been observed in Nd, either in the paramagnetic or magnetically ordered phases. A careful study of the inelastic scattering of neutrons from a new large single crystal of Nd (grown by the solid state electrotransport technique) has been carried out at the Institut Laue-Langevin. Quasielastic scattering which varies markedly with both wavevector and temperature has been found. This scattering has a maximum intensity around T N and exhibits a characteristic linewidth of some 0.4 meV. These results may be interpreted in terms of heavily-damped excitations within low-lying crystal field levels. At lower temperatures, and further from the satellite wavevectors, two weak but well-defined magnetic excitations have been observed.

Dynamical effects of the interaction between 4f electrons and optical phonons in rare-earth hydroxides, especially in Tb(OH)3and Nd(OH)3

The Raman spectra of single crystals of Nd(OH)3, Gd(OH)3, Tb(OH)3 and of Y(OH)3 have been investigated at helium temperatures and partially in external magnetic fields B<or=12 T. The Raman active optical frequencies have been assigned and the frequencies of the k=0 modes determined and correlated with the modes in the isomorphous rare-earth trichlorides. The interaction between the optical phonons and the 4f electrons becomes apparent in the magnetic phonon splitting in the zero-field frequency shift and, in favourable circumstances, in a phonon-electron anticrossing which depends on the magnetic field. In Tb(OH)3 all these effects can be observed simultaneously. In the same crystal the magnetic phonon splitting occurs spontaneously below its ferromagnetic Curie temperature. All effects can be treated theoretically using a Jahn-Teller type interaction Hamiltonian bilinear in the electron and phonon variables. The numerical values of the coupling constants have been found to agree for the different interaction effects. There are indications of a systematic variation of these numbers with the type of rare-earth ion and the phonon mode considered. The contribution of optical phonons to the effect of interionic energy transfer in Tb(OH)3 by virtual phonon exchange is considered and compared with the aforementioned results.

Thermoelectric power of Nd1−xLax and Ce1−xLax alloys

The thermoelectric power of polycrystalline double hexagonal-close-packed samples of Nd1−xLax and Ce1−xLax has been measured from 2 to 300 K. Single crystals of Nd have also been measured. These results confirm that there are at least two magnetic-transition temperatures in both sets of alloys. Data for Nd affirm there is a Néel temperature at 19.2 K and an incommensurate to commensurate transition at 7.5 K. These features are much less prominent in Ce and Nd thermopower data than corresponding features in the heavy rare earths. There is some anisotropy in the Nd single-crystal data, but the a- and c-axis data are similar in shape. In the Ce-rich Ce-La alloys there is a large positive peak at 75 K and a negative peak at ∼5 K.

Abstract: Thermoelectric power of Nd1−xLax and Ce1−xLax alloys

The thermoelectric power of polycrystalline dhcp samples of Nd1−xLax and Ce1−xLax has been measured from 2–300K. Single crystals of Nd have also been measured. (AIP)

Efficient cross pumping of Nd3+by Cr3+in Nd(Al,Cr)3(BO3)4lasers

Single crystals of Nd(Al1-xCrx)3(BO3)4 have been grown. The pump light is absorbed in the broad, intense Cr3+ absorption bands and transferred efficiently within less than 100 ns to Nd3+. The Nd3+ fluorescence lifetime is 19 mu s up to x=0.05, and decreases to 5 mu s for x=1. Compared with the x=0 crystals, the same Nd3+ inversion can be obtained with an order of magnitude reduction in the spectral power density of pump light for x=0.05.

Magnetothermodynamics of Nd(C2H5SO4)3⋅9H2O. IV. Determination of absolute temperature scales and other properties below 0.5°K with constant magnetic fields along the a crystal axis

The magnetic moment of a 3.930 cm diam spherical single crystal of Nd(C2H5SO4)3⋅9H2O (NES) has been measured below 0.5 °K after cooling by demagnetization from fields of 25, 15, 10, and 5 kG along the a crystal axis. Small amounts of irreversibility, believed to be due to the different rates of cooling of the 79.5% spin-free Nd3+ isotopes and the 20.5% Nd3+ isotopes with nuclear spin, was measured by ’’entropy gain,’’ enabling correction to true magnetic moments on isentropes. Equilibrium between the lattice and electron system was lost at fields of about 40 kG and temperatures below 0.5 °K. Entropy gain values were recorded for 0, 1000, 2500, and 5000 G on isoerstedics. An ’’Adiabatic Demagnetization-Sample Isolation-Calorimeter’’ was used to measure enthalpy as a function of entropy by means of electrical heating after demagnetization, thus enabling the derivation of thermodynamic temperature scales at zero and constant fields of 1, 2.5, and 5 kG as a function of entropy. The temperature-dependent component of the initial susceptibility, (χa,0−χa,T-ind), obtained from the magnetic moment data leads to the expression (χa,0−0.00576) = (0.3899/T)[1−0.0028/T −2.56×10−4/T2+5.06×10−6/T3−3.15×10−8/T 4] cm3/mole NES, which is valid down to 0.014 °K. The ’’high temperature’’ limiting magnetic component of the heat capacity was found to be CH=0(mag) =2.29×10−3/T2 −9.0×10−3/T3 gibbs/mole Nd3+. After correcting for the nuclear hyperfine structure term, 1.87×10−3 gibbs °K2/mole Nd3+, the dipole–dipole interaction term ADD=0.42×10−3 gibbs °K2/mole Nd3+. This, and the similar ADD=0.40×10−3 gibbs °K2/mole Nd3+ found from c-axis data, may be compared to the theoretical value, 0.396×10−3 gibbs °K2/mole Nd3+. The agreement shows that, aside from the hyperfine nuclear effect, the magnetic interactions are essentially ideal dipole–dipole. A heat capacity maximum occurred at 0.014 °K and zero field. The thermodynamic temperature, relative enthalpy, relative internal energy, heat capacity, and magnetic moment were tabulated as a function of entropy over the range 0.01–0.5 °K for zero field. Tabulations are also included for 1000, 2500, and 5000 G. Comments on the magnetic ground state of NES are given. Evidence for ’’frozen-in’’ magnetic structure at zero field and low temperature is presented.

Rotational-type spin reorientation in Nd&amp;lt;inf&amp;gt;1-x&amp;lt;/inf&amp;gt;Dy&amp;lt;inf&amp;gt;x&amp;lt;/inf&amp;gt;Co&amp;lt;inf&amp;gt;5&amp;lt;/inf&amp;gt;and its application to thermomagnetic generator

A rotational-type spin reorientation (SR) phenomenon is found in single crystals of Nd 1-x Dy x Co 5 , and the SR temperatures are controlled by Dy concentration near room temperature. In the SR temperature region an anomaly of a trapezoid shape is observed in specific heat, and it shows the second order nature of this phase transition. A thermomagnetic generator utilizing this phenomenon is invented, where thermal energy is converted directly into electric energy through the magnetic flux change accompanied with the SR. In an ideal case, the maximum energy that can be converted is evaluated as the magnetic anisotropy energy in the SR temperature region.