Transferred Hyperfine Interaction Research Articles

Anomalous transferred hyperfine interactions in bulk and epitaxial Tb:Y alloys: a NMR study

We have made an NMR study of the effect of yttrium substitution on the hyperfine splitting of in ferromagnetic terbium at 4.2 K. In conventionally prepared polycrystalline samples the average transferred hyperfine field increases linearly with yttrium content, an effect attributed to the reduction of the negative transferred hyperfine fields from the 4f spins on neighbouring Tb ions. The rate of increase, however, is about half of that expected from similar measurements on inter-rare-earth alloys. We have also studied the transferred hyperfine interaction in epitaxially grown laminae of Tb containing 5% and 10% Y, in which resolved satellites associated with individual nearest-neighbour Y atoms are observed. The satellite shift, per unit change in 4f spin, is less than half of that observed in epitaxially grown Ho:Dy and Ho:Gd alloys. We conclude that the nominally non-magnetic Y is not a simple spin diluent, and that it makes a substantial contribution to the transferred hyperfine field.

Temperature Dependence of Nuclear Magnetic Resonance and Transferred Hyperfine Field of 133Cs in a CsMnCl3 Single Crystal

AbstractThe nuclear magnetic resonance of 133Cs in a CsMnCl3 single crystal grown by the Czochralski method has been investigated by employing a Bruker FT NMR spectrometer. The resonance lines of two different Cs(I) and Cs(II) were recorded. The quadrupole coupling constants of Cs(I) and Cs(II) in CsMnCl3 decrease as the temperature increases. The temperature dependence of e2qQ/h is explained with a single torsional frequency of the Cs‐Cl ion by means of the simple Bayer theory. Also, we have investigated the transferred hyperfine interaction due to the transfer of spin density from the Mn2+ ion to the Cs+ ion in the CsMnCl3 single crystal using the magnetic susceptibility and the paramagnetic shift using nuclear magnetic resonance.

The Anomaly in the Knight Shift vs Susceptibility Plot of31PNMR in(CexLa1-x)P

Systematic 31 P NMR studies have been made on (Ce x La 1- x )P ( x =1.00, 0.90, 0.10, 0.02) using powders obtained from high-quality single crystals. For CeP, previously reported strong non-linearity of the Knight shift vs susceptibility plot, with an order of magnitude larger coupling constant A THI of the transferred hyperfine interaction (THI) at higher temperatures than at lower temperatures, has been confirmed to be an intrinsic property. For mixed systems, NMR spectra are composed of almost equally spaced several peaks. Detailed analyses of the spectra have shown that only the 1st-nearest-neighbor Ce ions contribute dominantly to the THI of 31 P in both the dense ( x =1.00, 0.90) and the dilute ( x =0.10, 0.02) systems. Despite this short-ranged THI, A THI varies dramatically between the two systems in quite a different way for the lower and the higher temperatures. Hence the large difference between the lower- T and the higher- T A THI in CeP becomes only a factor of ∼1.7 difference in the dilute s...

Transferred hyperfine interaction of 133Cs in a CsMnCl 3 single crystal

We have been investigated the transferred hyperfine interaction due to the transfer of spin density from the manganese ion to the cesium ion in CsMnCl 3 single crystal using the magnetic susceptibility and the paramagnetic shift using nuclear magnetic resonance. From these results, the transferred hyperfine field of 133Cs in CsMnCl 3 was obtained; the transferred hyperfine field of Cs(I) and Cs(II) are 820 Oe and −32 Oe, respectively, at room temperature.

Endor-investigations of rare earth and transition metal ions in the cubic elpasolite crystal Cs2NaYF6

The paramagnetic rare earth ions Yb 3+ , Ce 3+ and Gd 3+ and the transition metal ion Cr 3+ were investigated in the cubic elpasolite crystal Cs 2 NaYF 6 with ENDOR. The superhyperfine (shf) interaction parameters of the first 1 9F, 23 Na and 133 Cs shells were determined. In the case of Gd 3+ they were analyzed in an overlap model of the transferred hyperfine interaction including exchange polarisation.

Transferred hyperfine interaction and zero field splitting of the Gd 3+ ion in KY 3F 10

We have investigated the E.P.R. spectra of Gd 3+ in KY 3F 10 single crystal. Gd 3+ substitutes for Y 3+ in an eight-fold fluorine coordinated siteforming an antiprism (GdF 8) 5−. We have determined the fine structure and transferred hyperfine structure spin hamiltonian paramters. The former are discussed by using the superposition model of Newman and we compare our values with previous ones obtained for Gd 3+ center in other host crystals as in LiYF 4 and ReF 3 (ReLa, Ce, Pr, Nd) which allows us to propose intrinsic parameters for eightfold fluorine coordinated Gd 3+. The latter indicate some spin polarisation effect of the Gd 3+ 5s and 5p shells due to inner unpaired 4f 7 electrons.

Multiple magnetic phase transitions, dilute Fe hyperfine fields and europium valence instabilities in RMn2Si2-xGex, R=rare earth

Mossbauer studies of dilute57Fe and151Eu in RMn2Si2-xGex (R=La, Sm, Eu and Gd) at temperatures 4.2 K to 480 K have been performed. The diamagnetic iron and europium reveal the magnetic order of the Mn and rare earth sublattices through transferred hyperfine interactions. The57Fe studies show that in LaMn2Si2, LaMn2Ge2, and SmMn2Ge2 the Mn is magnetically ordered above the known Curie temperatures, and the compounds are antiferromagnets up to TN=470 K, 415 K and 385 K respectively. Studies of151Eu in R1-xEuxMn2Si2, (R=La, Gd) display Eu subspectra corresponding to Eu2+, Eu3+ and intermediate valant Eu. All display large magnetic hyperfine fields.

Transferred hyperfine fields in rare-earth-substituted YFe2 and YNi2

In the intermetallic compound YFe2, the metallic hyperfine field at the Y nucleus, as measured by 89Y NMR spectroscopy, is affected by the substitution of one or more neighbour Y atoms by different rare-earth impurities. In order to understand the underlying mechanisms for the transferred hyperfine interaction, we have performed first-principles calculations, within the local spin-density theory, for embedded clusters representing a Y atom and its vicinity in the compounds Y1-xRxFe2 (R=Gd, Tb, Ho, Tm or Lu) and Y1-xGdxNi2. The contact magnetic hyperfine field and the dipolar field were obtained; the resulting total held was found to increase with the spin of the rare-earth impurity. Orbital hyperfine fields were not considered. The contact transferred field was found to arise from direct polarization of the s electrons by the rare-earth spin.

29Si NMR and magnetic susceptibility of U 3Si 2

The magnetic susceptibility, Д m, of U 3Si 2 has been measured in the temperature range 4–1000 K. It exhibits a broad maximum ( T max ⋍300 K ) which may relate to the spin fluctuation process. Below T max the microscopic magnetic properties of U 3Si 2 have been investigated by the 29Si Knight shift ( K) and spin-lattice relaxation rate (1/ T 1). The Knight shift versus susceptibility relation gives a hyperfine coupling constant H hf=48 kOe/ μ B. From the extrapolated limit of the linear K vs Д m curve a large positive temperature-independent contribution to Д m is obtained. This is attributable to the Van Vleck-type orbital paramagnetism, to be expected in metals with unfilled degenerate bands. The temperature dependencies of Д m, K and (1/ T 1) give evidence for the fluctuations of the uranium 5f moments. The characteristic fluctuation rate is ~3 k B T max/ ħ when an effective number of uranium ions involved in the transferred hyperfine interaction is limited to first neighbours.

Study of magnetic relaxation in the perovskite SrLaFeSnO6by Mössbauer spectroscopy

The temperature dependence of the 57Fe and 119Sn Mössbauer spectra of SrLaFeSnO6 has revealed the existence of unusual magnetic relaxation behaviour. The transferred hyperfine interactions in the Sn resonance at 4.2 K establish that the Fe and Sn cations are disordered. An explanation is developed in terms of the formation of magnetic clusters below ca. 220 K which increase in size with decreasing temperature until a long-range ordered G-type antiferromagnetic structure is achieved below ca. 38 K. This behaviour is intermediate between a true antiferromagnet and a spin-glass. A reinterpretation of the related SrFe1 –xSnxO3 –y system is given which suggests that compositions in the region of Sr2FeSnO5.71 may also exhibit spin-glass behaviour.

89Y nuclear magnetic resonance study of hyperfine interactions in (R xY1−x)Fe2

89Y pulsed nuclear magnetic resonance measurements have been performed at low temperatures in (RxY1−x)Fe2 compounds, where R is a heavy rare-earth (Gd, Tb, Dy, Ho, Er, and Tm) in the range 0≤x≤0.05. The spectra were measured at 4.2 K, except for Dy (77.4 K). The spectra were analyzed in terms of direct and indirect (through common Fe neighbors) transferred hf interactions. The direct transferred hf field amounts to a few kOe per rare earth 1st neighbor; the indirect contributions of the first two shells are smaller by a factor of 10. We have found that a model that restricts the transferred hyperfine interactions to the indirect hf field or considers the first three neighbor shells in the same way is not satisfactory to explain the changes in the hyperfine field at Y nuclei.

55Mn, 125Te, and 113Cd NMR studies of the diluted magnetic semiconductor Cd1-xMnxTe in the range x=0.01-0.6.

$^{55}\mathrm{Mn}$, $^{125}\mathrm{Te}$, and $^{113}\mathrm{Cd}$ NMR has been used in the diluted magnetic semiconductor ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te (x=0.01--0.6) for probing into local electronic structure. The detection of $^{55}\mathrm{Mn}$ nuclei in the magnetically (3${\mathit{d}}^{5}$) and quadrupolar (I=5/2) broadened NMR spectra has been possible only at low frequencies because of the ${\mathrm{Mn}}^{2+}$-${\mathrm{Mn}}^{2+}$ exchange interaction, particularly in the antiferromagnetic clusters for high values of x (0.125--0.6). $^{125}\mathrm{Te}$, which undergoes transferred hyperfine interaction from ${\mathrm{Mn}}^{2+}$, could however be detected at high frequencies (94.88 MHz) for x=0.6 and 0.3. At these high x values, exchange within the clusters reduces the effective magnetic moment 〈${\mathit{S}}_{\mathit{z}}$〉 experienced by Te and consequently the broadening is within limits. The situation is quite different in $^{113}\mathrm{Cd}$, as ${\mathrm{Mn}}^{2+}$ is not the nearest neighbor nor is it bonded to Mn directly. However, it does undergo dipolar interaction with the ${\mathrm{Mn}}^{2+}$ spin and is also affected by the spin polarization of the sp band of CdTe by ${\mathrm{Mn}}^{2+}$. Thus $^{113}\mathrm{Cd}$ NMR has been detected for all x values. The shift changes sign between x=0.6 and x=0.3 in both Mn and Te, from positive to negative in Mn and negative to positive in Te as expected for direct versus transferred hyperfine interaction. The shift also changes sign in $^{113}\mathrm{Cd}$; as expected it parallels the Mn shift.

NMR and Susceptibility Studies of QuasicrystallineAl-Mn-Si-Ru Alloys

Magnetic susceptibility and nuclear magnetic resonance measurements have been made on quasicrystalline and crystalline phases of Al 62 Mn 20 Si 10 Ru 8 and Al 68 Mn 20 Si 6 Ru 6 alloys. The average value of local magnetic moment on Mn atoms and the spin-glass freezing temperature are not different so much between the two phases. However, static and dynamical properties of 27 Al NMR signals observed in the two phases are significantly different. These results suggest that most of the magnetic properties such as the formation of local magnetic moments and the magnitude of interactions between them are not closely related with the presence or absence of translational symmetry of the lattice; these properties might be related with local atomic configuration. A characteristic property of electrons in the present quasicrystals has been demonstrated by the transferred hyperfine interactions between Mn atoms and Al nuclei.

Electric quadrupole interactions of europium in alkali europium tungstates by Mössbauer and laser spectroscopies

151Eu Mossbauer spectroscopy and optical-r.f. double resonance spectroscopy measurements of the quadrupole interaction parameters in KEu(WO4)2 give good agreement and are of comparable accuracy, while laser heterodyne spectroscopy measurements provided improved accuracy by an order of magnitude. However in the crystallographically disordered compound NaEu(WO4)2, Mossbauer spectroscopy was more suited to producing fittable spectra. The difference in the hyperfine field of the two compounds in a 9 T applied field is attributed to a transferred hyperfine interaction.

Transferred hyperfine interaction of a Yb3+ trigonal centre in KMgF3

The investigation of a Yb3+ trigonal centre in KMgF3 was carried out by means of ENDOR. Expressions for the frequencies for ENDOR transitions in trigonally distorted complexes for arbitrary magnetic field orientation with respect to the crystallographic axes were obtained. A structural model of the centre was determined. The parameters of interaction of Yb3+ with F ions of the nearest environment were also determined. A method to determine the absolute signs of the crystal field parameters B43 and B63 was suggested. The microscopic calculation of crystal lattice deformation in KMgF3 near a paramagnetic impurity was carried out. The microscopic analysis of transferred hyperfine interaction parameters for an ion in a non-S state and having a local non-cubic symmetry, taking into account the effects of the spin polarisation of the outer filled 5s and 5p shells of the rare-earth ion, has been carried out for the first time.

8 9Y nuclear-magnetic-resonance measurements in (DyxY1−x)Fe2 compounds

In a previous work, 89Y measurements at 4.2 K in (RxY1−x)Fe2 compounds, with R=Tb and Ho and 0.05≤x≤0.20, have shown broad nuclear-magnetic-resonance (NMR) spectra, due to transferred hyperfine interactions. 89Y NMR signals could not be observed with R=Dy in the same composition range. In the present work, compounds were prepared with Dy in the concentration range 0.005≤x≤0.02 to investigate the origin of this anomaly. Compared to the pure YFe2 compound, the observed NMR spectra are broadened and show a shift towards higher frequencies. With increasing Dy concentration, the NMR signals fall very rapidly. Magnetization measurements at 4.2 K were performed in samples with Tb, Ho, and Dy; the results indicate that the behavior of the Dy compounds is qualitatively different in the low-magnetic-field region of the curves, requiring a minimum applied field to start increasing the magnetization. The NMR data and the magnetization results of the Dy compounds can both be explained as arising from a much lower mobility of the domain walls.

119Sn Mössbauer studies in antiferromagnetic La 2CuO 4

Mössbauer Spectroscopy (MS) studies of 119Sn were carried out in antiferromagnetic La 2(Cu .99Sn .01)O 4. The 1 at% 119Sn 4+ impurity in the form of SnO 2 was first diffused in CuO, and its substitution for Cu 2+ was confirmed. Spectra recorded at T> 120 K show a single site quadrupole splitting. At T < 120 K, a magnetic interaction is observed, reaching a saturation with hyperfine field, H eff = 8.7 KOe at T ≤ 30 K. From the combined quadrupole-magnetic interaction at T ≤ T N, both the η-parameter and the angle ϑ formed by q zz and H eff were determined. The significance of the transferred hyperfine interaction in terms of spin-structure is outlined. The feasibility of applying 119Sn MS as a microscopic probe in the Cu-O layers and its comparison with corresponding 57Fe MS is discussed.

Quenching of magnetic fluctuations around 119Sn impurities in superconducting GdBa 2(Cu 0.99Sn 0.01) 3O 7

Mössbauer Spectroscopy studies with 119Sn substituted for Cu in GdBa 2(Cu 0.99Sn 0.01) 3O 7 ( T c = 90 K) reveal the occurrence of a transferred hyperfine interaction at temperatures below 60 K. The effective magnetic field is 8.3 KOe at 57 K and decreases gradually with decreasing temperature to 6 KOeat 16 K. The onset of the magnetic interaction at the non-paramagnetic 119Sn probe is explained in terms of local depletion of holes due to the Sn 4+ doping, consequently quenching the magnetic fluctuations around the impurity. These experimental findings provide strong evidence for spin-spin correlations originating from the Cu 2+ moments and present in the superconducting state.

31P NMR Studies of the Magnetically Ordered Heavy-Electron Compound YbP

The microscopic magnetic properties of the heavy-electron compound YbP have been investigated by 31 P NMR at temperatures from 0.38 to 600 K. The observations of both an abrupt decrease of 1/ T 1 at around 0.7 K and additional broadening of the spectrum below this temperature show that YbP orders magnetically at low temperatures. In the paramagnetic state, the Knight shift vs susceptibility plot exhibits a marked change of the slope at around 100 K with a larger hyperfine coupling constant of -4.02 kOe/µ B below 100 K. Based on a semimetallic band structure of the compound, a simple model is presented, in which the previously observed anomalous broad maximum in the low-temperature specific heat is ascribed to the Kondo effect due to a large mixing between a \(\varGamma_{6}\) ground state of 4f hole of Yb 3+ ion and occupied P-derived 3p states in the valence bands. The contribution of this p-f mixing mechanism to the transferred hyperfine interaction is also evaluated.

Electric Properties of Ladder Type Polymers BBB and BBL

ABSTRACTWe report on ESR and electric conductivities of BBB and BBL ladder polymers with emphasis on the former. Both the ESR and the electrical conductivities are strongly anisotropic suggesting that the polymer backbones are plannar. The ESR data implies the existence of two different types of spin species. The hyperfine spectrum of one of these species is analyzed in terms of a Spin Hamiltonian and anisotropic transferred hyperfine interaction with the 14N nuclei (I = 1). We found that “annealing” the BBB and BBL films to high temperatures, To, increase the spin susceptibility for To ≤ 850K (BBB). However annealing to To ≥ 900K results in a dramatic reduction in the spin susceptibility and dramatic incise in the conductivity. The room temperature in-plane conductivity of annealed samples at To ≥ 900K exceeds σ = 1 Ω−1 cm−1. This high intrinsic conductivity is probably associated with the formation of cross-linked condensed aromatic structure. The 'phase transition” temperature to this structure is higher by 50K for BBB compared to BBL. The conductivity versus temperature of annealed samples (700K ≤ To) can be described by the onisotropic version of Mott's law for variable range hopping. We demonstrate that the anisotropic conductivity is due to the anisotropic localization lengths (ξ∥ and ξ⊥) of the wave function of the localized states.