Pr Magnetic Moments Research Articles

Analysis for Magnetization of Ce1-xRxFe2(R= Pr, Nd) Based on NMR Study

We have carried out 141 Pr and 143 Nd NMR measurements on Ce 1- x R x Fe 2 (R = Pr, Nd) at 1.4 K. The hyperfine fields of Pr and Nd remain nearly constant in the measured concentration ranges: 0.15 ≦ x ≦0.43 and 0.1 ≦ x ≦0.4 for Pr and Nd compounds, respectively. The hyperfine fields analysis combining with 57 Fe Mossbauer effect results give the magnetic moments of Pr and Nd in the compounds to be about 2.6 µ B and 2.8 µ B , respectively. The magnetizations of Ce 1- x R x Fe 2 are estimated and discussed.

Superconductivity and normal-state magnetic properties of Pr-dopedBa1-xKxBiO3 single crystals

Superconductivity and normal-state magnetic properties of Pr-dopedBa1-xKxBi1-y PryO3 single crystals have been studied.With Pr doping, Tc decreases rapidly following the Abrikosov-Gor'kov(AG) theory up to Pr concentrations of ytr≈3.5 and 1.5% forcrystals with x = 0.40 and 0.53, respectively, but they relax and deviatefrom the AG-formula curves above ytr before dropping to 0 K. For thenormal-state magnetic susceptibility, the Curie-Weiss temperature changessign from positive to negative values above ytr, whereantiferromagnetically coupled Pr magnetic moments blunt the suppression ofTc. The effective magnetic moments of Pr calculated from the observedCurie constants, which are 1.0 µB and 1.2 µB for x = 0.40 andx = 0.53, suggest a strong crystal field effect. The Pr doping alsoenhances the Pauli susceptibility.

Valence band studies of the RTX (R=Pr, Nd; T=Cu, Ag, Au; X=Ge, Sn) compounds

The valence band in the RTX (R=Pr, Nd; T=Cu, Ag, Au; X=Ge, Sn) compounds was studied by the X-ray photoemission spectroscopy. The XPS data were compared with the ones calculated using the spin-polarized tight-binding linear muffin-tin orbital (TB LMTO) method. The obtained results show that the valence bands are determined mainly by the Cu 3d, Ag 4d and Au 5d bands. The calculation of the total energy for two models of the crystal structure: an ordered of the LiGaGe-type and a disordered one of the CaIn 2-type indicates that in the RTSn (T=Cu, Ag ,Au) compounds the LiGaGe-type structure is stable. Calculated value of the Pr magnetic moment is smaller than that of the free Pr 3+ ion value, whereas the Nd magnetic moment is equal to the free Nd 3+ ion value.

Growth of large PrBa 2Cu 3O 7− δ single crystals by modified TSSG method using zirconium dioxide crucibles

Bulk PrBa 2Cu 3O 7− δ single crystals of 2.5 g weight were seed-grown by modified TSSG technique using yttria stabilized zirconium dioxide crucibles. A chemical composition analysis revealed a visible yttrium substitution (from the seed and crucible material) of Pr atoms to x=0.2–0.3 in the Pr 1− x Y x Ba 2Cu 3O 7− δ formula. Neutron diffraction and X-ray diffraction measurements showed the block structure of different disorientation along the [0 0 1]- and [1 0 0]-directions. FWHM of the rocking curve on (0 0 6) reflection is 0.9° by neutron diffraction and 0.5° by X-ray diffraction. FWHM of the rocking curve on a (2 0 0) reflection is 0.3° by X-ray diffraction. The antiferromagnetic ordering of Pr magnetic moments was found at a temperature T N=11 K by neutron diffraction. It was attempted to change the cation distribution and to increase the c -lattice parameter in a Pr123 crystal by fast crystallization. At a cooling rate of 200 K/s the c -parameter increased from 11.68 to 11.75 Å, which is insufficient for a possible appearance of superconductivity in this crystal.

Mössbauer Spectroscopy and Radiofrequency Absorption Investigations of Pr Substituted 1-2-3 Type Compounds

Abstract 57Fe and 151Eu Mossbauer spectroscopy as well as RF susceptibility measurements were applied to study the effects of Pr substitution either into the rare earth or into the Ba site in Eu1–x Pr x Ba2Cu3O7– and EuBa2–x Pr x Cu3O7–, respectively. Site mixing of Pr between the rare earth and Ba sites could be excluded by the utilization of 57Fe Mossbauer spectroscopy. It was found that there exists a correlation between the 151Eu isomer shift and the onset temperature of the superconducting transition independent of the location of Pr. RF susceptibility measurements provide an evidence for a difference in the magnetic moment of Pr substituted for the Eu or Ba sites. The obtained results can be explained by hole filling as the dominant effect of Pr substitution.

Magnetic Anisotropy of PrNi5 Single Crystal at Millikelvins

Magnetic ordering in the hyperfine enhanced nuclear ferromagnet PrNi5 was investigated in external magnetic fields up to 72 mT at temperatures from below the ordering temperature up to about 20 mK. An anisotropy of the magnetization and ac susceptibility was observed for two single crystalline samples having a or c crystallographic axis parallel to the external field. The results show that the nuclear magnetic moments of Pr are ordered in the basal plane of the hexagonal crystal structure of PrNi5.

Kondo effect in Y1−xPrxBa2Cu3O7

The low temperature resistance measurements on Y1−xPrxBa2Cu3O7 compounds for x=0.45 polycrystalline sample and x=0.5 epitaxial film are reported. Upturns in the resistance-temperature (R-T) curves are observed above Tc for both the two samples. Careful analysis shows that the R(T) behavior above Tc could be well fitted by an expression of R0+AT+BlnTK/T. The existence of BlnTK/T term indicates that the upturns above Tc are due to the Kondo interaction between Pr magnetic moments and mobile holes in the system. The result coincides with the specific heat measurements reported earlier.

Crystallographic data and magnetic properties of new CeFeSi-type RMnGe compounds (R = FaSm) studied by magnetization and neutron diffraction measurements

Investigations made by powder X-ray diffraction, susceptibility measurements and neutron diffraction experiments on new ternary RMnGe (R = LaNd) are reported. They crystallize in the well-known tetragonal CeFeSi-type structure (space group P4/nmm). This structure, which is closely related to the ThCr 2Si 2-type structure, can be described as isolated “ThCr 2Si 2 blocks” connected via R-R contacts. All these compounds are antiferromagnetic below T N ∼ 410 K (not detected in the bulk susceptibility measurements). At room temperature, the magnetic structures are characterized by a stacking of antiferromagnetic (001) Mn layers with Mn magnetic moments (about 3.6-3.2 μ B at 2 K) at 40° (CeMnGe) or along the c axis. In all cases, this antiferromagnetic arrangement of the Mn sublattice persists down to 2 K. At lower temperature, the R sublattice orders in ferromagnetic (001) layers, with various ordering schemes along the stacking axis. At 150 K, PrMnGe exhibits ferromagnetic behaviour followed by a ferro-antiferromagnetic transition below 80 K simultaneously with a crystallographic phase transition (tetragonal to orthorhombic symmetry). Below 200 K, NdMnGe exhibits a ferromagnetic ordering of the Nd sublattice which persists until 2 K. Within the complete ordering temperature range, the Pr and Nd magnetic moments are in the basal plane with a magnitude of 2.45(3) and 3(1) μ B for Pr and Nd, respectively, at 2K. The magnetic structures correspond to the sequence Mn(AF)R(+)R(+)Mn(AF)R(−or+). The Mn moments rotate at 50° from the c axis in PrMnGe, while they are in quadrature in NdMnGe. In CeMnGe, the Ce-sublattice orders antiferromagnetically below about 130 K (not detected in the magnetometric measurements), yielding the following ordering scheme: Mn(AF)Ce(+)Ce(+)Mn(AF)Ce(−)Ce(−); at 2 K the Ce moment value is 2.2(1) μ B. The Mn and Ce moment directions are almost parallel, and make an angle of about 35° with the c axis. The results are discussed and compared to those obtained previously on the corresponding ternary silicides and germanides of the CeFeSi- and ThCr 2Si 2-type structures.

NMR study of magnetic properties of Pr 2Fe 14B

141Pr NMR measurements have been done on Pr 2Fe 14B and (Pr 0.9Lu 0.1) 2Fe 14B at 1.4K by the spin-echo method. The observed hyperfine fields in Pr 2Fe 14B are 2574 and 2803kOe for the f and g sites, respectively, and in (Pr 0.9Lu 0.1) 2Fe 14B 2560 and 2804kOe for the f and g sites, respectively. The hyperfine fields due to the 4f shell of the Pr 3+ ion were evaluated taking into account the transferred hyperfine field from the Fe sublattice. The magnetic moments of Pr 3+ in Pr 2Fe 14B were estimated to be 2.9 and 3.0μB for the f and g sites, respectively.

The Kondo anomaly in the low temperature specific heat of Pr doped YBCO

Low-temperature specific heat measurements on Y 1−xPr xBa 2Cu 3 O 7 as a function of temperature T for X=0.2, 0.45, 0.6 with 90mK<T< 30K are reported. The specific heat of this system consists of a nuclear Schottky anomaly, a Pr magnetic Kondo anomaly and the background contribution. The large linear term of specific heat has been found to be connected with Kondo scattering of the mobile hole carriers by Pr magnetic moments. The spin-1 character of the Kondo specific heat anomaly indicates that the Pr valence state is close to +3 in the Y 1−xPr xBa 2CuO 7 system. The Tc depression and metal-insulator transition are believed to be attributed to the localization due to the interaction of Pr 4f electrons with hole carriers in CuO 2 planes.

Magnetic structures of PrMn 2Si 2 and NdMn 2Si 2 from neutron diffraction studies

The magnetic properties of PrMn 2Si 2 and NdMn 2Si 2 have been reinvestigated. Below T N (368 and 381 K for PrMn 2Si 2 and NdMn 2Si 2 respectively) the previously proposed antiferromagnetic ordering taking place on the manganese sublattice is confirmed. Neutron diffraction experiments show that the Pr magnetic moments do not order above 1.6 K, while a ferromagnetic ordering of the neodymium sublattice occurs at T C = 33(2) K (μ Nd = 2.83(4) μ B at 1.6 K). The magnetic coupling between the two sublattices is mainly ferromagnetic, with the easy axis of the magnetic structure aligned along the c axis, but a slight antiferromagnetic coupling remains between the Mn moments in the (001) plane (μ Mn,F = 1.4 μ B and μ Mn, AF = 0.8 μ B at 1.6 K).

Origin of Tc suppression and magnetic ordering in PrBa2Cu3O7- delta.

The magnetic 4f excitation spectrum of ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ was measured by use of inelastic neutron scattering in a study of the ground-state properties of praseodymium. We analyzed the spectra in terms of crystal-field transition lines of a trivalent Pr ion. The absolute widths of the magnetic transition lines were found to be enhanced compared with those in stable R${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ compounds, where R is a rare-earth element. A distinct \ensuremath{\Vert}Q\ensuremath{\Vert} dependence of the inelastic magnetic intensities was found due to spatial magnetic correlations even above the unexpectedly high ordering temperature of the Pr magnetic moments. Both the enhanced width and the magnetic correlations are almost independent of the oxygen concentration. The enhanced widths indicate an increased hybridization between 4f electrons and electrons of the ${\mathrm{CuO}}_{2}$ planes. This is certainly responsible for the ${\mathit{T}}_{\mathit{c}}$ suppression in ${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$, probably indirectly through the unexpectedly strong magnetic correlations (high ordering temperature) of the Pr magnetic moments caused by this enhanced hybridization.

On the pressure dependence of Tc of the Y 1- xPr xBa 2Cu 3O 7-δsystem

It is shown that the crossover which occurs with increasing x near x ≃ 0.2 in the pressure dependence of the superconducting critical temperature T c from positive to large negative values for the Y 1- x Pr x Cu 3O 7-δ (δ ≃ 0.05) system can be be accounted for using a simple phenomenological model, generalized to include pressure. The model was developed to describe the dependence of T c on the concentrations of Pr ( x) and Ca ( y) and Ca ( y) in the Y 1- x- y Pr x Ba 2Cu 3O 7-gd system and incorporates (1) the counteracting effects of the generation and annihilation of holes in the conducting CuO 2 planes by Ca 2+ and Pr n+ ions (where + n is the Pr valence), respectively, and (2) the deparing of superconducting electrons via exchange scattering of the mobile holes in the CuO 2 planes by the Pr magnetic moments. New measurements of T c(P) on higher quality Y 1- x Pr x Ba 2Cu 3O 7-δ specimens are presented and analyzed in terms of the phenomenological model. The increase in the magnitude of the normal state electrical resistivity with pressure observed in an Y 0.5Pr 0.5Cu 3O 7-δ specimen is consistent with the decrease in the mobile hole concentrations with pressure inferred from the model.

Hole filling and pair breaking by Pr ions in YBa2Cu3O6.95+/-0.02.

Measurements of the superconducting critical temperature {ital T}{sub {ital c}} are reported for the (Y{sub 1{minus}{ital x}{minus}{ital y}}Ca{sub {ital y}})Pr{sub {ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} system as a function of {ital x} and {ital y}. The {ital T}{sub {ital c}} vs {ital c} curves at fixed values of {ital x} can be resolved into two contributions: (1) the counteracting effects of generation and filling of holes in the CuO{sub 2} sheets by Ca{sup 2+} and Pr{sup 4+} ions, respectively, and (2) the depairing of superconducting electrons via exchange scattering of the mobile holes in the CuO{sub 2} sheets by the Pr magnetic moments.

Micro+ spin resonance in single crystal PrNi5: Evidence for local moments at Ni sites.

Well resolved multifrequency ${\mathrm{\ensuremath{\mu}}}^{+}$ spin-resonance spectra were observed as function of field direction and temperature in a single crystal of ${\mathrm{PrNi}}_{5}$. Two interstitial ${\mathrm{\ensuremath{\mu}}}^{+}$ positions were identified. A ${\mathrm{P}}_{\mathrm{x}}$(cos\ensuremath{\theta}) term, in addition to ${\mathrm{A}}_{0}$, is sufficient to describe the angular dependence. Neither the angular dependence nor the temperature dependence of the shifts can be accounted for by Pr magnetic moments. Evidence is provided for magnetic moments at Ni sites, contradicting prevailing views.

Comparison of inelastic magnetic neutron scattering on PrBa 2Cu 3O 7 and NdBa 2Cu 3O 7

Inelastic magnetic neutron scattering on these compounds reveals for Pr and Nd crystal-field (CF) splittings of the order of 30–40 meV. While NdBa 2Cu 3O 7 exhibits sharp CF transitions allowing for a fully determined CF scheme, the Pr magnetic moment in PrBa 2Cu 3O 7 shows the typical features of instability, which we account for the total T C suppression in this compound. As in ErBa 2Cu 3O 7, we found in NdBa 2Cu 3O 7 a non negligible density of states of conduction electrons at the rare earth site (N(E F)J ex = 0.0125). In addition, the quasielastic response below T C looks mainly like a Gaussian line, which we attribute to antiferromagnetic correlations in analogy to other magnetically ordering rare earth systems.

Magnetic susceptibilities of UO 2[sbnd]Pr 2O 3 solid solutions

Magnetic susceptibilities of Pr y U 1− y O 2+ x solid solutions ( y ≤ 0.1) with fluorite-type structure were measured from 4.2 K to room temperature. From the analysis of the magnetic susceptibility data, it was found that the oxidation state of uranium was tetravalent or pentavalent and that of praseodymium was trivalent. The susceptibilities of oxygen-stoichiometric solid solutions (Pr y U 1− y O 2) increased with Pr concentration ( y) in the whole temperature range measured, indicating the magnetic moment of Pr 3+ is larger than that of U 4+. The susceptibilities of solid solutions with low Pr concentrations ( y ≤ 0.07) increased with decreasing temperature down to ca. 31 K, and showed discontinuous change (susceptibility drop) at ca. 30–31 K ( T d temperature). Below this temperature, after a little decrease, the magnetic susceptibilities increased again with decreasing temperature. This increase of susceptibility below T d temperature is considered to be due to the U 5+ ion formed in the solid solutions.

Structure and magnetism of the Pr 2Fe 14- xCo xB system

Isostructural, tetragonal materials were synthesized for the entire composition range ( x = 0 to 14). They were studied by X-ray and magnetometry methods. Magnetization measurements confirm a ferromagnetic arrangement of 3d and Pr magnetic moments and reveal a sharp increase of the Curie temperature with the increase of Co concentration. Saturation magnetization at 295 and 77 K reaches a slight maximum around x = 1 and gradually decreases for higher Co content. Anisotropy fields initially decrease and afterwards increase very quickly as more Co is introduced to the system. A spin reorientation occurs in alloys with x ⩾ 9.5 at temperature higher than 660 K. It marks a transition between uniaxial anisotropy and planar anisotropy. Spin reorientation temperature becomes lower for materials with higher Co content. A discussion of the Curie temperature change is conducted in terms of preferential substitution of Co into 16k 2 sites. The weakening of the exchange interaction between Pr and 3d sublattices, as well as the decreasing Pr-sublattice anisotropy with rising temperature, are considered to be responsible for anisotropy field changes. The interplay between crystal field and exchange field interactions is emphasized. A comparison with the Nd 2Fe 14- x Co x B system is included.

Magnetic Properties of Pr1-cLacAl2

The magnetic properties of the pseudobinary system, Pr 1- c La c Al 2 , have been investigated in order to know the combined effect of the crystal field and magnetic dilution of Pr by La in PrAl 2 . The Pr concentration dependence of the Curie temperature and magnetic moment of Pr 3+ in Pr 1- c La c Al 2 are reported and discussed in terms of the crystalline electric and molecular fields, suggesting that PrAl 2 has a bunched state as the ground state. A set of crystal field parameters in PrAl 2 is proposed to be x =0.81 and W =-0.53 meV.

Structural and magnetic characteristics of the pseudobinary system PrMn 2ErMn 2

Alloys were prepared by induction melting and subsequent annealing at 950 °K. Replacement of Er by Pr in ErMn 2 results in increasing lattice parameters in the hexagonal MgZn 2-type structure. From Pr 0.283Er 0.05Mn 0.667 to Pr 0.163Er 0.17−Mn 0.667 the alloys crystallize with a cubic face-centered structure with lattice parameters from 12.308 to 12.601 Å, isotypical with Th 6Mn 23 (G-phase). This is also the structure of (TmPr)Mn 2. PrMn 2 crystallizes as α-Mn type (χ-phase), body-centered cubic, with a = 8.902 A ̊ at 950 °K, and as G-phase with a = 12.690 A ̊ at 1000 °K. In the liquid He range, Pr and Er magnetic moments align antiferromagne-tically in the MgZn 2-type structure. High saturation moments at 4.2 °K in the face-centered cubic, phase suggest complex behavior. These alloys show two Curie temperatures around 60 ° and 420 °K and remain ferromagnetic above room temperature. Neutron diffraction at 4.2 ° and 300 °K does not reveal antiferromagnetic ordering within crystallographic sites. Some kind of magnetic order may be retained beyond 1000 °K. The compounds do not follow the Curie-Weiss law to 1000 °K. PrMn2 (χ-phase) has a Weiss constant of —80 °K and may order antiferromagnetically below 4.2 °K on Pr sites.