Location and associated hyperfine properties of μ+ in La2CuO4

The location of the positive muon used as a probe in highT _c systems is investigated using the unrestricted Hartree-Fock cluster procedure. Our calculations indicate that ⁺ is located in thea–c plane at a distance of 1.08 Å from the apical oxygen at a ⁺-O(a)-Cu angle of 25°. The hyperfine field at this site is also calculated. Our results show the importance of including the local contact and dipolar contributions to the hyperfine field which arise from the unpaired electron spin distribution in the vicinity of the muon.     

Theory of location and associated hyperfine properties of the positive muon in La2CuO4

The current understanding regarding the location of the positive muon, which is a valuable tool for probing the magnetic properties of copper oxide superconducting systems, will be reviewed for La₂CuO₄. The results of our present investigations by the Unrestricted Hartree-Fock Cluster procedure, which leads to a location for the muon of about 1.08 Å away from an apical oxygen and with the O-⁺ direction making an angle of 25° with the O-Cu direction, will be discussed, including the magnitude and direction of the hyperfine field obtained from the calculated wave functions. These latter results, which are in reasonable agreement with earlier muon spin rotation data in powdered samples and recent data in single crystals, show the importance of including the local contact and dipolar contributions to the hyperfine field associated with the unpaired electron spin distribution in the neighborhood of the muon. Possible additional factors besides those included here, that will involve substantial computational efforts but could lead to a bridging of the remaining quantitative differences with experimental hyperfine data, will be discussed.     

Pac studies of spin deviations,pressure induced hyperfine field shifts,and temperature variation of supertransferred hyperfine fields

A PAC study of¹¹¹Cd substiuted antiferromagnetic transition metal salts is reported. Supertransferred hyperfine fields at¹¹¹Cd nuclei were used for the first time to observe three effects: zero-point spin deviations, temperature variation, and pressure shift of the hyperfine field. Comparison of KNiF₃ and RbMnF₃ with their corresponding quadraticlayer fluorides K₂NiF₄ and Rb₂MnF₄ yields an estimate for the magnitude of the zeropoint spin deviation in doped antiferromagnets. The temperature dependences of the Cd hyperfine fields in RbMnF₃/Cd and MnF₂/Cd have been determined. The shift in hyperfine field observed for -MnS/Cd under external pressure further supports our model for the origin of the supertransferred hyperfine fields.This work was supported by the US Energy Research and Development Administration.     

The lattice location and hyperfine field of implanted Yb in Fe as a function of annealing temperature

A combined study has been made of the lattice location and hyperfine field of Yb implanted into Fe single crystals. The location has been determined by ion channeling and back-scattering, the hyperfine field by perturbed angular correlation (PAC) measurements on¹⁶⁹Yb (decaying to excited states in¹⁶⁹Tm). The channeling experiments indicate that initially about 60% of the Yb atoms occupy substitutional sites in the Fe lattice, while the remaining atoms are not in any specific crystallographic site. On annealing, Yb migrates from substitutional to non-substitutional sites. No Yb atoms remain substitutional after a 600°C anneal. By making PAC measurements at two temperatures for two - cascades in¹⁶⁹Tm, it is found that the PAC pattern can be described using a combined static and time-dependent magnetic interaction. The PAC results show that the average hyperfine field and relaxation parameter decrease on annealing, and that the field disappears after a 600°C anneal. The correlation between the location and the hyperfine field is discussed. A comparison of the results with previous Mössbauer results for¹⁵¹Gd implanted in Fe, together with relaxation parameter measurements on a¹⁶⁹Yb₂O₃ source, suggests that the non-substitutional Yb is internally oxidized in the Fe host.Work partly carried out while at the Clarendon Laboratory, Oxford, England and Nuclear Physics Division, AERE, Harwell, England.     

57Fe NMR spectra in domain walls of hexagonal ferrites with magnetoplumbite structure

The domain wall NMR spectra of⁵⁷Fe were measured on polycrystalline samples of BaFe₁₂O₁₉ and SrFe₁₂O₁₉ at 4·2 K. We have calculated the anisotropy of the hyperfine field dipolar component. The measured NMR spectra were interpreted supposing that the hyperfine field anisotropy is caused only by the dipolar field anisotropy.     

Mössbauer effect studies of Tb<Subscript>0.27</Subscript>Dy<Subscript>0.73</Subscript>(Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)2 intermetallics at 295 K

The synthesis of materials and the studies of crystal structure and ⁵⁷Fe Mössbauer effect were performed for Tb_0.27Dy_0.73(Fe_1?x Co _x )₂ intermetallics. Terfenol-D (Tb_0.27Dy_0.73Fe₂) is the starting compound of this Fe/Co-substituted series. X-ray measurements showed evidence of a pure cubic Laves phase C15, MgCu₂-type, and unit cell parameters were determined across the series. A Co substitution introduced local area, at sub-nanoscale, with random Fe/Co neighbourhoods of the ⁵⁷Fe atoms.Mössbauer effect spectra for the Tb_0.27Dy_0.73(Fe_1?x Co _x )₂ series at room temperature are composed of a number of locally originated subspectra due to the random distribution of Fe and Co atoms in the transition metal sublattice, and due to [1 1 1] an easy axis of magnetization. Isomer shift, magnetic hyperfine field and quadrupole interaction parameter were obtained from the spectra, both for the local area and for the bulk sample.As a result of Fe/Co substitution, a Slater-Pauling-type curve for the average magnetic hyperfine field vs. Co content was observed. It was found that the magnetic hyperfine fields corresponding to the local area also create a dependence of the Slater-Pauling-type vs. Co contribution in the Fe/Co neighbourhoods.     

The183Re ground state dipole moment and nuclear spin-lattice relaxation of Re in Fe

The hyperfine interaction of the system¹⁸³Re(70d)Fe has been investigated with the NMR/ON technique. With the hyperfine field valueB _hf(ReFe)=–76.0(1.5) T the ground state magnetic moment was determined as: (5/2⁺,¹⁸³Re)=+3.12(6) _N. The field dependent nuclear spin-lattice relaxation time has been measured. The result for the high-field relaxation rateR _exp=1.65(5)·10^–15 T ²s K^–1 is explained in terms of indirect spin-wave interaction.     

57Fe NMR in Y3Fe4.5Ga0.5O12 single crystal

The angular dependence of the⁵⁷Fe NMR spectra in a single crystal of Ga substituted YIG is studied with special attention paid to the satellite lines of the octahedral iron. These satellites correspond to ferric ions in the neighbourhood of which the Ga³⁺ ion is located. The anisotropy of the hyperfine field of these satellites is in accord with the prediction of the independent bond model. A simple analysis indicates that the main source of the anisotropy, besides the dipolar interaction, is the change of the supertransferred part of the hyperfine field.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.     

The temperature dependence of the Mössbauer hyperfine parameters in Nd2Fe14B

We have determined the temperature dependence of the internal hyperfine field, isomer shift, and quadrupole shift at each of the six iron sites in Nd₂Fe₁₄B. The hyperfine parameters are consistent with the local iron site environments. The quadrupole and isomer shifts and their temperature dependences support our assignments of the relative ordering of the internal hyperfine fields as j₂>k₂>ck₁>j₁>c. We obtain a Mössbauer temperature of 390 K for Nd₂Fe₁₄B, which compares well with the Debye temperature of 420K for pure iron.     

Hyperfine field calculations: Search for muon stopping sites in Fe3O4

Muon Spin Rotation (SR) results for magnetite (Fe₃O₄) are analyzed and discussed. At room temperature, a SR signal is observed due to the presence of an internal magnetic field (B_int) at the muon site. External transverse field measurements show that B_int is parallel to the magnetic spin direction, the <111> direction in zero applied field. Calculations of the hyperfine field to pinpoint muon stopping sites in magnetite show that the local field contains supertransfer (covalent) and dipolar field contributions. The implanted muons appear to stop at sites structurally similar to those reported for hematite (-Fe₃O₄), where muon-oxygen bond formation was strongly indicated.Research partially supported by US Department of Energy     

The magnetic hyperfine field of lutetium in iron by NMR/ON

Nuclear magnetic resonance of oriented¹⁷⁷Lu in iron has been found with a sample prepared by on-line implantation of¹⁷⁷Lu in iron at T<0.2 K. The broad resonance, FWHM=20.5 (1.3) MHz, has a centre frequency of _L=355.06 (51) MHz at zero external field. With the g-factor of¹⁷⁷Lu g=0.637 (3) from literature the magnetic hyperfine field of Lu in Fe is derived as B_hf=–73.12(36) T. Static nuclear orientation data are not compatible with a two site model where the nuclei which are oriented experience the hyperfine interaction found in NMR/ON. A fraction with a lower hyperfine field is necessary to explain the data.     

Excited Muonic Atom Scattering: New Adiabatic Approach

New results on the applied field dependence of the NMR of ⁷⁵Se implanted in pure iron and oriented at millikelvin temperatures are reported. They yield the magnetic hyperfine field acting on Se nuclei present as dilute impurities in the iron matrix and the magnetic dipole moment of the 5/2⁺ ground state of ⁷⁵Se with significantly improved precision. The results are B _hf(SeFe) =+67.9(10)T and ||(⁷⁵Se) =0.683(10)_N. The improved value of the hyperfine field, with data from[2], gives the magnetic dipole moment of the 9/2⁺ ground state of ⁷³Se as ||=0.892(13)_N.     

Dipolar relaxation in an ultra-cold gas of magnetically trapped chromium atoms

We investigate, both theoretically and experimentally, dipolar relaxation in a gas of magnetically trapped chromium atoms. We find that the large magnetic moment of 6_B results in an event rate coefficient for dipolar relaxation processes of up to 3.2×10^-11 cm³s^-1 in a magnetic field of 44 G. We present a theoretical model based on pure dipolar coupling, which predicts dipolar relaxation rates that agree with our experimental observations. This very general approach can be applied to a large variety of dipolar gases. PACS 34.50.-s; 34.50.PI; 03.65.NK; 32.80.PJ     

Spin and temperature dependence of the magnetic hyperfine field of Cd in the rare earth-aluminum Lavesphase compounds RAl2

Perturbed angular correlation spectroscopy has been used to investigate the combined magnetic and electric hyperfine interaction of the probe nucleus ¹¹¹Cd in ferromagnetically ordered rare earth (R)-dialuminides RAl₂ as a function of temperature for the rare earth constituents R=Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er. In compounds with two magnetically non-equivalent Al sites (R=Sm, Tb, Ho, Er), the magnetic hyperfine field was found to be strongly anisotropic. This anisotropy is much greater than the anisotropic dipolar fields, suggesting a contribution of the anisotropic 4f-electron density to magnetic hyperfine field at the closed-shell probe nucleus. The spin dependence of the magnetic hyperfine field reflects a decrease of the effective exchange parameter of the indirect coupling with increasing R atomic number. For the compounds with the R constituents R=Pr, Nd, Tb, Dy and Ho the parameters B₄, B₆ of the interaction of the crystal field interaction have been determined from the temperature dependence of the magnetic hyperfine field. The ¹¹¹Cd PAC spectrum of EuAl₂ at 9 K confirms the antiferromagnetic structure of this compound.     

Hyperfeinstruktur im HolmiumÄthylsulfat

In holmium ethylsulfate diluted with lanthanum ethylsulfate we have investigated the transition⁵ I ₈→F ₅ at 4,2 ?K using a combination of a Fabry-Pérot-interferometer and a high resolution grating spectograph. The hyperfine structure splitting of four lines was resolved; the hyperfine structure parameters for the two lowest crystal field levels of the⁵ I ₈ groundterm were determined.     

The C hyperfine constants of HCS and HSC studied by microwave spectroscopy

The ¹³C hyperfine constants of the H¹³CS and HS¹³C radicals are determined by microwave spectroscopy. For H¹³CS, the 1₀₁-0₀₀ rotational transition is measured at 38.5 GHz with a Fourier transform microwave spectrometer, and two ¹³C hyperfine constants are determined. They are well interpreted in terms of a relatively large HCS bonding angle (132.8°). For HS¹³C, the N=7-6, 9-8, and 10-9 rotational transitions are measured in the 268-384 GHz region by using a source modulation spectrometer combined with a free-space discharge cell, and five ¹³C hyperfine constants including the nuclear spin-rotation constant, C_aa, are determined. From the ¹³C hyperfine constants, the p character of the unpaired electron orbital on the carbon atom is estimated to be 66.5%, supporting a classical resonance picture; .     

Influence of radiation damage on the hyperfine field of triton irradiated nickel foils

The recently observed Mössbauer effect in⁶³Ni enables the study of the hyperfine field in nickel with high resolution. In the present paper, the line broadening of the Mössbauer resonance is analyzed in order to study the influence of radiation damage on the magnetic hyperfine field in⁶⁴Ni foils. Each of these foils was irradiated by tritons at 15 K with a total current integral of 2.4 A h in order to produce the short-lived⁶³Co sources (T _1/2=27 s). An upper limit of 4.6 kG was estimated for the standard deviation of the magnetic hyperfine field distribution which resulted from the accumulated radiation damage. For the annealed absorber material the standard deviation of the magnetic field is less than 53 G.     

Nuclear magnetic moment of 12 d 11/2− 131mXe

NMR-ON measurements were performed on^131mXe (I=11/2^–; T_1/2=12.0 d) in Fe, the sample being prepared by recoil implantation after the¹³⁰Te(,3n)^131mXe compound reaction at E=40 Mev. The hyperfine splitting _NB_HF/h¦, extrapolated to zero external magnetic field, was found to be 209.9(1) MHz. Taking B_HF=+1523(8) kG for the hyperfine field of XeFe, the magnetic moment of^131mXe is deduced to be (–)0.994(5) _N. As a byproduct, the zero-field hyperfine splitting of^129mXe (I=11/2^–; T_1/2=8.9d) in Fe was measured as 188.1(1) MHz, with which a magnetic moment of (–)0.891(5) _N is deduced for^129mXe.     

NMR-ON on196,197m,198,198m,200mAu in Fe and Ni

The zero-field hyperfine splitting frequencies of a series of Au isotopes in Fe and Ni have been determined with nuclear magnetic resonance on oriented nuclei. The results are:. For¹⁹⁸Au(2^–) in Fe the quadrupole splitting could be resolved. The results are ¦g_NB_HF/h|=259.48 (3) MHz and e²qp/h=–2.08(4) MHz. Our measurements show that most hyperfine splittings published on these isotopes have been incorrect. The quadrupole splitting of¹⁹⁸AuFe disagrees in magnitudeand sign from the value reported by single-passage NMR on oriented nuclei. The following nuclear quantities are deduced: (^197mAu,11/2^–)=5.98(9) _N; (^198mAu, 12^–)=5.85(9) _N; (^200mAu, 12^–)=5.90(9) _N; Q(¹⁹⁸Au,2^–)/Q(¹⁹⁹Au, 3/2⁺)=1.37(3). Our measurements show further that the non-contact hyperfine field for Au in Ni is smaller than assumed previously, and that the magnetic hyperfine splitting frequency of¹⁹⁷AuFe known from NMR is inconsistent with the magnetic hyperfine splitting frequencies of^{198, 199}AuFe.     

A Mössbauer effect study of the Sb impurity site hyperfine field in amorphous Fe80B20

Mössbauer effect was used to determine the Sb site hyperfine field in the amorphous ferromagnet Fe₇₉SbB₂₀. The¹²¹Sb Mössbauer spectrum at 77 K showed a distribution of hyperfine fields with a most probable value of 219 kOe. This result is discussed in terms of the systematics of non-magnetic site hyperfine fields in ferromagnets.⁵⁷Fe Mössbauer effect was also used to determine the most probable value of the Fe site field, , and the width of the field distribution, H. Our measurements yield 280 kOe and H=104 kOe. These results are consistent with previous results on the amorphous ferromagnet Fe₈₀B₂₀.