Nuclear Orientation Studies of Magnetism in Single Crystal Pr0.5Nd0.5Ni

The angular distributions of -rays from ¹⁴²Pr, ¹⁴⁷Nd and ¹⁴⁴Pm in Pr_0.5Nd_0.5Ni were investigated by means of low-temperature nuclear orientation. The results show that the Pr and Nd electronic moments order along the c- and a-axis, respectively. Pm ions introduced as a very dilute magnetic impurity, preferentially align with the Nd ions.     

Non-collinear spin DFT for lanthanide ions in doped hexagonal NaYF4

Trivalent lanthanide ions (Ln³⁺) doped in hexagonal (β)-NaYF₄ nanocrystals (Na₂₄Y₂₃Ln₁F₉₆, Ln = La, Ce, Pr, Nd, Pm, Sm, Eu, Gd) were systematically studied by density functional theory (DFT) with a perturbative account for spin–orbit coupling. The simulated results, including the optimised molecular structures, electronic and magnetic properties, are compared to previous spin-polarised DFT studies in the same system. The spin–orbit coupling effects become significant with the increase in the number of unpaired 4f electrons in the doped lanthanide ions, particularly for the Sm³⁺-, Eu³⁺- and Gd³⁺-doped nanocrystals. Abnormal behaviour of Eu³⁺-doped nanocrystals was observed due to the Wybourne–Downer mechanism. A ‘sandwich-like’ 2p–4f–4d,5d electronic structure for Na₂₄Y₂₃Ln₁F₉₆ and the energies of the highest occupied 4f electrons from Ce³⁺ to Gd³⁺ are consistent with Dorenbos's relationship. The energy difference between the first and second Russell–Saunders terms (^2S+1L) of the lanthanide dopant is consistent with Carnall's experimental results and with earlier spin-polarised DFT calculations.     

States inN=80140Nd populated in the decay of140Pm

The level structure of theN=80,¹⁴⁰Nd has been investigated through the beta decay of^140m Pm and^140g Pm, whose decay half-lives were measured to be 5.95±0.05 min and 9.1±0.5 sec, respectively. Decay schemes for the two isomers have been constructed fromγ-ray measurements. With the help of the beta decayft values and internal conversion electron measurements, spins and parities were deduced for levels in¹⁴⁰Nd. Among the levels a 7^? state at 2222.0 keV and a 5^? state at 2273.3 keV are identified as two-neutron quasiparticle states. The (ie233-01) for^140m Pm and^140g Pm have been deduced as 7^? and 1⁺, respectively. From beta end-point measurements, the decay energies of the two isomers have been determined asQ _EC=6.48±0.07 MeV^140m (Pm) andQ _EC=6.08±0.10 MeV (^140gPm). The results are discussed in the light of nuclear systematics of theN=79 and 80 isotones.     

Decay of the 4.2-min152Pm into levels of152Sm

After bombardments of enriched¹⁵²Sm with 14-MeV neutrons, three isomers of¹²⁵Pm reaction, have been observed with half-lives of 4.2±0.2 min, 7.5±0.2 min and 15.0±1.0 min. Sources of pure 4.2-min¹⁵²Pm were obtained by separating the promethium from its parent 11-min¹⁵²Nd produced by thermal-neutron induced fission of²³⁵U. The beta and gamma radiations of the 4.2-min¹⁵²Pm have been investigated using semiconductor and scintillation spectrometers. Most of theγ-ray transitions could be placed in a level scheme for 152Sm. Especially interesting is a level at 1083 keV for which the assignmentI ^π=0⁺ is proposed. In a 4πβγ experiment, the ground state feeding of¹⁵²Sm in theβ ^?-decay of the 4.2-min¹⁵²Pm has been measured to be 61% of allβ-ray transitions. AQ _β-value of 3.4±0.2 MeV has been obtained.     

Characterization of isomers of the nucleus154Pm

Consideration of the expected two-quasiparticle structures and their estimated band head energies, and the selection rules for beta transition rates for the¹⁵⁴Nd →¹⁵⁴Pm →¹⁵⁴Sm decays are used to deduce the configurations for the isomers and the low-spin structures in the neutron rich doubly odd nucleus ₆₁ ¹⁵⁴ Pm₉₃. The 2.68 m high spin isomer and the 1.73 m low spin isomer are respectively assigned the spin-parity 4⁺ and 1⁺ with the configuration {p:5/2⁻ [532↑] +n:3/2⁻ [521↑]} with the 2.68 m isomer lying lower in energy, and thus forming the¹⁵⁴Pm ground state. Two-quasiparticle character of the beta-connected states in¹⁵⁴Nd decay and¹⁵⁴Pm decay is discussed.     

Radioactive decay of 1.7-h149Nd to levels of transitional149Pm

Sources of¹⁴⁹Nd were produced by thermal-neutron irradiation of enriched¹⁴⁸Nd. High resolution Ge(Li) spectrometers were used to collect gamma-ray singles and coincidence spectra in the study of the decay of 1.7-h¹⁴⁹Nd. A total of 214 gamma rays have been assigned to the decay of¹⁴⁹Nd, and 201 of these transitions have been placed in a level scheme of¹⁴⁹Pm involving 42 excited states. Absolute values for the beta-group intensities were determined for transitions to the¹⁴⁹Pm levels, and spin and parity assignments were made for many of the observed states. The experimentally determined level structure of¹⁴⁹Pm was compared with corresponding levels in other odd-mass Pm and Eu nuclides. Interpretations were made in terms of the core-coupling model. Radioactive decay¹⁴⁸Nd(n, γ)¹⁴⁹Nd; measuredE _γ,I _γ,γ-γ coinc.¹⁴⁹Pm deduced levels,J,π. Compton-suppression. Ge(Li) detector. Enriched targets.     

Theoretical search for half-metallic material: Y MnS3

Half-metallic material, perovskite sulfide Y MnS₃, is theoretically discovered. Our calculated results show that the ground state is the ferromagnetic state with a high estimated Curie temperature of about 869 K, and the ground-state structure exhibits Pm3m space group with no Jahn–Teller distortion. The ferromagnet behaves as half-metal with an energy gap of 1.30 eV at the Fermi level in the down-spin band. Additionally, Mn ions are in the high-spin state with the chemical valence state of Mn³⁺.     

Orbital Electron Capture Rate and Time Modulation of H- and He-like Ions in a Storage-Ring

We have studied in a heavy ion storage ring the orbital electron capture decays of H- and He-like ¹⁴⁰Pr and ¹⁴²Pm ions and found that the H-like ions with one electron in the K-shell decay 1.49(8) and 1.44(6) times faster, than the corresponding He-like ions with two electrons in the K-shell. This result is explained by spin statistics due to the hyperfine structure of the H-like ions.     

The magnetic dipole moment of the 91 keV state of147Pm

The magnetic dipole interaction of the 91 keV state of¹⁴⁷Pm in an environment of metallic neodymium has been investigated by a time-differential perturbed angular correlation (TDPAC) experiment. The measurement was performed in an external magnetic field of 2.94 (3) T at room temperature. From the Larmor precession frequency the magnetic dipole moment of the 91 keV state is derived as =+3.22(16) _K. The enhancement of the external magnetic field by the paramagnetic 4f shell determines the ionicity of the Pm ion as Pm³⁺ in metallic and as Pm⁴⁺ in non-metallic sources.     

Magnetic anisotropy of Pm impurity in rare earth–nickel compound

Low-temperature nuclear orientation was applied to study hyperfine interactions of ¹⁴²Pr, ¹⁴⁷Nd and ^143,144Pm nuclei in Pr^0.5Nd^0.5Ni single crystal. Angular distributions, temperature dependence and external magnetic field effects on the γ-ray anisotropy are presented. A Nd-Pm exchange interaction seems to dominate the magnetic properties of Pm ions in this system. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pressure induced antiferromagnet-ferromagnet transition in La<Subscript>0.5</Subscript>Ba<Subscript>0.5</Subscript>CoO<Subscript>2.8</Subscript> cobaltite

The anion deficient cobaltite La_0.5Ba_0.5CoO_2.8 with theformal cobalt valence state close to 3+ has been studied as function of pressure up to6.5 GPa at different temperatures by neutron powder diffraction. At ambient pressure thecrystal structure of this compound has cubic symmetry (space group Pm3?m) and is found to become antiferromagnetic withT _N close to 250 K. Applied pressure inducesa gradual transition from the antiferromagnetic into a ferromagnetic state through a mixedmagnetic state. The transition is not accompanied by obvious changes in the macroscopiccrystal symmetry. It is suggested that the magnetic ground state strongly depends on theunit cell volume and that the transition is associated with a spin state crossover of thecobalt ions whereas the formal Co³⁺/Co⁴⁺ ratio is less importantthan expected following the double exchange scenario for the appearance offerromagnetism.     

New states and γ-transitions in 209Bi observed in the (3He, d*γγ)-subcoulomb-reaction

High-spin states in ¹⁴³Pm have been investigated via the ¹²⁸Te(¹⁹F,4nγ)¹⁴³Pm reaction using techniques of in-beam γ-spectroscopy. γ-ray singles, γ-γ coincidences, γ-ray anisotropies and DCO ratios have been measured. Based on these measurements, the level scheme of ¹⁴³Pm has been extended up to an excitation energy of 10535.4 keV, including 48 new γ-rays deexciting 28 new levels. The yrast levels in ¹⁴³Pm can be understood qualitatively in the framework of a weak-coupling model. Received: 10 July 2000 / Accepted: 12 October 2000     

Decay of the very neutron-deficient isotope 131Pm

The decay of ¹³¹Pm has been investigated by means of γ-ray spectroscopy. The ¹³¹Pm nuclei were produced by fusion-evaporation reaction of ¹⁰⁶Cd(³²S,3p4n) at the beam energy of 170 MeV. A helium-jet technique and a tape transport system were used to collect the activities and transfer them to a detecting position for X and γ rays measurement. Two γ rays of 185.0 and 220.0 keV were unambiguously identified to follow the β⁺ decay of ¹³¹Pm by results of X-γ and γ–γ coincidence. A growth-decay feature of the decay curve for 87.8 keV γ-ray of ¹³¹Nd confirmed the production of ¹³¹Pm nuclei. The half-life of ¹³¹Pm was measured to be 6.3 ± 0.8 s. A partial decay scheme of ¹³¹Pm is proposed on the basis of X-γ and γ–γ coincidence data in this experiment and the known structure information deduced from in-beam experiments of the daughter nucleus ¹³¹Nd. Received: 11 January 1999 / Revised version: 20 May 1999     

Shape evolution in odd-A 137 Pm

The odd mass nucleus ¹³⁷Pm has been studied to high spins through the ¹⁰⁹Ag(³²S, 2p2n)¹³⁷Pm reaction at an incident beam energy of 150 MeV. The de-exciting ??-rays were detected using an array of 18 Compton suppressed clover detectors. The level scheme of ¹³⁷Pm has been extended up to $J^\pi = \tfrac{{43}} {2}^ -$ and excitation energy of E _x ? 6 MeV with the observation of 42 new gamma transitions. The linear polarization (IPDCO) measurements for the ??-ray transitions have been done for the first time. The spin and parity assignments for most of the reported levels have been made using these results and the coincidence angular anisotropy (R_DCO) measurements. The nuclear shape evolution is discussed in the light of Total Routhian Surface (TRS) and Cranked Shell Model (CSM) calculations.     

Orbital electron capture decay of hydrogen- and helium-like Pm ions

The β⁺${\beta }^{+}$ and orbital electron-capture decays of stored hydrogen- and helium-like ¹⁴²Pm ions have been measured. So far, such measurements have been performed with only one nucleus, namely ¹⁴⁰Pr. The electron-capture decay constant of hydrogen-like ¹⁴²Pm⁶⁰⁺ ions is about 50% larger than that of helium-like ¹⁴²Pm⁵⁹⁺ ions, which is in excellent agreement with the previous measurements in ¹⁴⁰Pr ions and with new theoretical predictions.     

On-line nuclear orientation of the deformed neutron-deficient Eu,Sm and Pm isotopes

Low-temperature nuclear orientation measurements made on-line at the SERC Daresbury Laboratory on^142m Eu,^141m Sm, and¹⁴¹Pm, with known magnetic dipole moments, have yielded the magnitude of the hyperfine fields of these isotopes in an iron host lattice. Thus measurements for the isotopes^{139, 138}Eu,^139m Sm, and¹³⁸Pm yielded values for the respective magnetic moments. Limits on the thermal relaxation times of Eu and Sm isotopes in Fe were also deduced. The results for¹³⁸Eu appear to contradict the earlier πh_11/2⊗νh_11/2 ground-state configuration assignment.     

Decay of oriented149Nd and levels in theN=88149Pm nucleus

Levels in the¹⁴⁹Pm nucleus populated via¹⁴⁹Nd decay were studied using the low temperature nuclear orientation technique. The parent¹⁴⁹Nd nuclei were oriented in a gadolinium host. The normalized gamma-ray intensities were determined for twenty five transitions in the daughter¹⁴⁹Pm nucleus. The spins of the¹⁴⁹Pm levels at 288.2 and 425.3 keV were determined as 9/2 and 7/2, respectively, and for several other¹⁴⁹Pm levels the previous spin-assignments could be unambiguously confirmed. Substantial new information on multipole mixing ratios of gamma-transitions in¹⁴⁹Pm is presented. Low-energy level spacing in the¹⁴⁹Pm nucleus is found to be in reasonable agreement with recent particle-rotor model calculations including the variable moment of inertia.     

Luminescence of yttrium aluminum borate single crystals doped with manganese

The optical absorption and luminescence spectra of single crystals of yttrium aluminum borate YAl₃(BO₃)₄ doped with manganese ions are measured. It is established that the optical absorption spectra of yttrium aluminum borate single crystals doped with manganese ions are determined primarily by the contribution from the Mn⁴⁺ ions. The luminescence spectra of the YAl₃(BO₃)₄ single crystals doped with manganese exhibit narrow lines attributed to the Mn⁴⁺ ions and an extended multiband structure which is associated primarily with the contribution from the Mn²⁺ ions.     

A novel scheme to acquire enhanced up-conversion emissions of Ho3+ and Yb3+ co-doped Sc2O3

A detailed investigation about the effect of Sc₂O₃: 1 mol%Ho³⁺/5 mol%Yb³⁺ co-doped with Ce⁴⁺ ions prepared by sol-gel methods was performed systematically. Under the excitation of 980 nm laser diode, both green emission (553 nm, ⁵F₄/⁵S₂→⁵I₈) and red emission (672 nm, ⁵F₅→⁵I₈) were both observed in the emission spectra of the samples, which were found to be two-photon process and sensitized by Yb³⁺ ions. With the increasing of Ce⁴⁺ ions, the up-conversion green emission intensity are increased by 6.52, 8.69, 10.85, 13.92 and 16.66 fold, corresponding to the Ce⁴⁺ ions concentrations from 5 mol% to 13 mol%, respectively. The number of photons are necessary to populate the upper emitting state decreases to 2 and the infrared absorption coefficient is reduced, when the Ce⁴⁺ ions concentration increase to 13 mol%. Ce⁴⁺ ions play an important role in tailoring the local crystal field around Ho³⁺ ions, lowering the highest phonon cut-off energy of matrix and reducing the infrared absorption coefficient, thus hindering the non-radiative processes, which contribute to the increased emission intensity. The excellent enhancement makes it a promising multifunctional optical luminescence material.