Muon hyperfine interactions in magnetic oxides

Muon spin rotation studies on magnetic oxides among which-Fe₂O₃ and Fe₃O₄ have shown that at temperatures below approximately 500 K the muons form a muon-oxygen bond, analogous to a hydrogen bond. Generally, the muon hyperfine interactions in magnetic oxides can be explained in terms of supertransfer (hyperfine) and dipole fields. Supertransfer fields result from covalent bonding effects. For the rare earth (R) orthoferrite series (RFeO₃) comparison is made with Mössbauer results on covalency effects in hyperfine interactions. Suggestions for next stages of experimentation in solid state research in oxides bySR are mentioned.     

Mixed hyperfine interactions in Fe-Mg-O: magnetic behaviour

The complex Mössbauer spectra exhibited by Fe_xO (x0.91) and (Fe_1–y Mg _y )_xO (y=0.15–0.85) powder samples at liquid helium temperature have been analysed by a Hamiltonian treatment to allow for the significant electric field gradients present at the Fe²⁺ defect sites. The magnetic behaviour of the defect clusters are considered in terms of antiferromagnetic couplings, consistent with the spin glass-like behaviour reported recently for magnesiowüstite.     

Observation of spin relaxation and magnetic ordering by transferred hyperfine interactions

Mössbauer measurements on ¹²⁹I in iodo (bispyrrolidinedithiocarbamato) Fe^III show the occurence of magnetic ordering at 2.18°K and relaxation effects in the paramagnetic region. The transition is confirmed by measurements on ⁵⁷Fe. The effective magnetic field at the ¹²⁹I nucleus at 1.4°K is 66^± 2kG and is perpendicular to the direction of the iron-iodine bond. The number of p and s holes in the (5s)² (5p)⁶ valence shell of iodine is determined from the values of the quadrupole coupling constant and the isomer shift.     

The magnetic hyperfine fields of rare earth ions in metals

Data for the magnetic dipole hyperfine interaction of essentially single rare earth ions in metals, measured with different experimental methods, are collected and discussed. Depending on the host, the magnetic hyperfine field of these paramagnetic ions remains undisturbed by the environment, or it is enlarged, or weakened or can even become completely lost. If there are magnetic ions in the neighbourhood, the magnetic interaction can enlarge the hyperfine field of the single ion by a transferred hyperfine field. The reason of the demagnetization effect may be crystal field splitting and hybridization. The core polarization field of the free rare earth ions is redetermined from measurements of the hyperfine interaction in nonmagnetic metals at low magnetic ion concentration.     

Local magnetic states and hyperfine interactions in Fe/Ti magnetic superlattices

Multilayer Fe/Ti films are synthesized by deposition in a Penning discharge. Measurements are made of thhe static hysteresis loops and Mössbauer spectra on Fe⁵⁷ nuclei. The hyperfine magnetic field distribution functions are calculated. It is established that the spontaneous magnetization of Fe/Ti magnetic superlattices undergoes very strong oscillations as a function of the Ti layer thickness. Three groups of peaks are noted in the hyperfine field distribution functions, corresponding to three nonequivalent states of the Fe ions, in one of which these ions do not have a characteristic magnetic moment. These results also agree with measurements of the temperature dependence of the magnetization in weak magnetic fields. For some Ti interlayer thicknesses the saturation magnetization scaled to the Fe content is much higher than the saturation magnetization of bulk Fe.     

The influence of time dependent effects on the longitudinal decoupling of free hyperfine interactions

The Scherer-Blume theory has been extended to arbitrary symmetries of the hyperfine interaction. In particular its influence on the longitudinal decoupling effect is shown.     

Influence of a surfactant on hyperfine magnetic interactions in goethite nanoparticles

Structural and magnetic characteristics of nanosized goethite (α-FeOOH) samples prepared by chemical precipitation of an iron (III) salt and alkali in aqueous solutions with different contents of a surfactant (ethyl alcohol) have been investigated. Changes in the morphology, structure, and sizes of antiferromagnetic nanoparticles, caused by the presence of the surfactant in the deposition solution, have been established by Mössbauer spectroscopy, magnetic measurements, X-ray diffraction, and electron microscopy. It is determined that an increase in the surfactant concentration leads to the bimodal size distribution of nanoparticles; in this case, the fraction of small (<10 nm) isolated particles in the sample increases and the degree of ordering of larger particles (50–100 nm) increases with a change in their shape from spherical to needle-like.     

Mössbauer isomer shifts,hyperfine interactions,and magnetic hyperfine anomalies in compounds of iridium

The dependence of the isomer shift of the 73 keVγ-rays of¹⁹³Ir on the oxidation state was studied in a variety of compounds of trivalent and tetravalent iridium as well as in IrF₅ and IrF₆. The observed shifts can be attributed to the sielding effect of the varying number of 5d electrons, but there may be additional direct contributions fromσ-bonding electrons. In the hexahalogen complexes with Kramers-degenerate electronic groundstates magnetically ordered phases were found and studied at temperatures between 0.5 and 4.2 K. Between IrF₆ and tetravalent [IrCl₆]^2? and [IrBr₆]^2? complexes magnetic hyperfine anomalies of up to 10% were observed, which support the presented interpretation of the hyperfine fields in terms of core polarization, orbital and spin-dipolar contributions.     

Calculation of the hyperfine structure of heavy H and Li like ions

The present status of calculations of the hyperfine splitting and the transition probability between the hyperfine splitting components in hydrogen and lithium like ions is discussed. The results of the calculations are compared with recent experimental data. A special attention is focused on the hyperfine splitting in hydrogen like lead and lithium like bismuth. It is shown that the theoretical prediction for the ground state hyperfine splitting in lead based on the single particle nuclear model for the Bohr-Weisskopf effect is in fair agreement with experiment. The theoretical prediction for the ground state hyperfine splitting in lithium like bismuth is improved due to more accurate calculations of the interelectronic interaction, QED, and nuclear corrections. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molecular oxygen spin-lattice relaxation in solutions measured by proton magnetic relaxation dispersion

Proton spin-lattice relaxation rate constants have been measured as a function of magnetic field strength for water, water-glycerol solution, cyclohexane, methanol, benzene, acetone, acetonitrile, and dimethyl sulfoxide. The magnetic relaxation dispersion is well approximated by a Lorentzian shape. The origin of the relaxation dispersion is identified with the paramagnetic contribution from molecular oxygen. In the small molecule cases studied here, the effective correlation time for the electron-nuclear coupling may include contributions from both translational diffusion and the electron T(1). The electron T(1) for molecular oxygen dissolved in several solvents was found to be approximately 7.5 ps and nearly independent of solvent or viscosity.     

An active magnetic channels system for in-beam study of hyperfine interactions

An active magnetic channels system has been constructed, in which the beam deflection is compensated by a pair of electromagnets close to the main magnet together with a steering magnet upstream. The residual beam deflection on the target is estimated to be ¦Δφ¦≤0.6°.     

Calculation of magnetic exchange interactions in Mott-Hubbard systems

An efficient method of computing magnetic exchange interactions in systems with strong correlations is introduced. It is based on a magnetic force theorem that evaluates linear response due to rotations of magnetic moments and uses a generalized spectral density functional framework allowing us to explore several approximations ranging from local density functional to exact diagonalization based dynamical mean field theory. Applications to spin waves and magnetic transition temperatures of 3d metal mono-oxides as well as high-T(c) superconductors are in good agreement with experiment.     

Calculation of the magnetic hyperfine structure in the ground electronic state of HCCO

In this paper we analyze the spin-spin hyperfine interaction in the two components of the ground electronic state of the free π radical HCCO, A²A′[²Π] and X²A″. Electronic mean values of the Fermi contact constants of all magnetic nuclei [¹H, ¹³C₁, ¹³C₂,¹⁷O] are calculated using models that include the electron-correlation correction, primarily CCSD method in the cc-pwCVTZ basis set and B3LYP functional in the cc-pCVQZ basis set. Also, we have calculated components of the anisotropic hyperfine tensor for the ground X²A″ state. The dependence of hyperfine coupling constants (HFCCs) on the two bending coordinates is examined, and the results of HCC bending (vibrational) averaging of electronic mean values are presented for both states. It is demonstrated that electronic and subsequent vibrational averaging of the HFCCs suffices for obtaining results that are in good agreement with available experimental findings (for proton) in the X²A″ state, owing to a small geometry dependence of these quantities, and relatively distant minimum from linearity.     

Temperature and pressure dependence of magnetic and electric hyperfine interactions in metallic Samarium

The magnetic and electric hyperfine interaction at¹¹¹Cd impurities in Samarium has been investigated by TDPAC measurements. The quadrupole frequency is _Q=20.0(2) MHz at 290 K and has a linear temperature dependence with the same slope (dln_Q/dT)_290K=–7.3(2) 10^–4 K^–1 in the rhombohedral and the hcp phase. The pressure dependence up to 7 kbar is (dln _Q/dT)=+8.7(1.4) 10^–3 kbar^–1. The magnetic hyperfine field of¹¹¹Cd in Sm is H_hf=242(6) kG at 4.2 K. Its temperature dependence confirms the existence of 2 different magnetic phases in Sm. The crystal field parameters B ₂ ⁰ and B ₄ ⁰ have been estimated from a comparison of H_hf(T) with molecular field models. The TDPAC spectra in the magnetic phases suggest that the impurities preferentially occupy the hexagonal Sm sites.