Calculations of hyperfine fields

First principle methods for calculation of hyperfine fields in different systems are reviewed. The contributions from energy states close to the Fermi level are emphasized and are responsible for different observed systematic behaviours in the hyperfine field, not directly related to the host magnetic moment. Calculations on Fe, on Fe₂P, on surfaces, on impurity atoms in Fe and on the muon Knight shift in Sb are discussed.     

Systematics of Mössbauer hyperfine parameters in Np intermetallics

Data for intermetallic compounds of neptunium obtained with the 60 keV Mössbauer resonance of²³⁷Np are reviewed. Measurements of temperature, pressure and field dependencies are available. The main questions addressed are: (a) the degree of delocalization of 5f-electrons, (b) the formal charge state of Np, and (c) the influence of the ligand on the neptunium electronic structure. For this purpose, we present an evaluation of systematic behavior concerning mainly the hyperfine field and isomer shift in the cubic Laves phase materials NpX₂, the NaCl-type monochalcogenides and monopnictides, and intermetallics with AuCu₃ and ThCr₂Si₂ structures. Analogies to corresponding rare-earth compounds will be pointed out.     

Magnetic hyperfine fields in ferrigehlenites

Western Canadian cretaceous coal (WC5) and Appalachian carboniferous coal (AC4) are good coking coals, although their rheological properties predict a different behaviour with this respect. According to Mössbauer Spectroscopy, iron-based mineral matters of these coals are very different: WC5 spectrum exhibits chiefly Fe₃O₄ while AC4 contains mainly ferrous silicate and no ferric ion. However the spectra of the ashes exhibit a similarity: they characterize α-Fe₂O₃ with a distribution of particle sizes extended down to some tens of nanometers. Such a dispersion could favour catalytic processes during the low temperature stages of coking.     

Transient hyperfine magnetic fields

Fast ions traversing magnetized materials experience very large transient hyperfine magnetic fields. The processes responsible for these interactions are related to the interchange of electrons between the moving ion and the polarized medium. The dependence of the transient hyperfine fields on the atomic number and the velocity of the ion, and on the magnetization of the host has been mapped for a wide range of nuclei and magnetic hosts. The experimental evidence supporting specific models will be presented and applications to the measurement of magnetic moments of short-lived excited states will be described. Supported in part by the National Science Foundation     

Interpretation of hyperfine fields in concentrated ferromagnetic alloys

A simple physical interpretation is given for hyperfine fields systematics at the sites of nonmagnetic ions in concentrated ferromagnetic alloys. Application is made to Heusler alloys and numerical results are given.     

Calculated hyperfine fields of light interstitials in Fe

Super-cell band structure calculations with the Korringa-Kohn-Rostoker method in the framework of the local-spin-density approximation are performed on ferromagnetic iron with typical elements (B, C andN) at the octahedral interstitial sites for the purpose of studying hyperfine fields of light interstitials. Lattice relaxations around the interstitial atoms are allowed in these calculations. Calculated hyperfine fields of these interstitial impurities are in better agreement with experimental values than the results obtained previously for unrelaxed lattices, showing that the inclusion of the lattice relaxation is crucial in these systems.     

First-principles calculations of the hyperfine fields on ligands in fluorides

In solid-state physics, a crystal lattice is frequently approximated by an array of interacting ions. In this case, the wave functions of individual ions are assumed to be a fairly good zeroth approximation in calculating the matrix elements of the interaction Hamiltonian of electrons and nuclei of the lattice from first principles. Use of the second-quantization method is proposed for such calculations in the basis of these functions. As an example, the electron transition amplitude from a ligand to the central ion is estimated. The results agree well with the experimental data.     

Magnetic hyperfine fields at sp-impurities in cobalt and nickel

Hyperfine Interactions - The understanding of magnetic hyperfine fields (B hf) at impurity nuclei in magnetic materials has been a central problem in nuclear solid state physics for the last...     

Muon hyperfine fields in iron and its dilute alloys

The temperature dependence (240 to 633 K) of the interstitial magnetic field, B_μ, as determined by the rotation of the spin of the μ⁺, has been measured for dilute polycrystalline iron alloys with Mo, Ti and Nb additions. In all cases the behaviours differ from one another and from the Fe(A1) alloys previously studied. B_μ, which is negative with respect to the magnetization, is increased in magnitude by A1 and Mo, and decreased greatly by Ti. The addition of Nb creates a two- phase alloy from which we can assess the role of heterogeneity and/or strain on B_μ in iron. If the temperature dependence of the hyperfine field B_hf extracted from B_μ for Fe(Mo) alloys is interpreted on the model previously used to discuss the Fe(A1) data, we would conclude that the muon is attracted to the Mo atom while repelled by the A1 atoms as the temperature decreases. Measurements giving room temperature values of B_μ for iron alloys with Mn, Cr, V and W taken after annealing above the recrystallization temperature are also reported.     

Hyperfine fields of 5sp shell impurities substituting Sb in the Heusler alloys Pd2MnSb and PdMnSb

Measurements of the hyperfine magnetic fields B_hf of Te and I impurities substituting Sb in the Heusler alloys Pd₂MnSb and PdMnSb clearly establish that the curve of B_hf versus impurity atomic number is shifted to the right by about 1 unit of atomic number for PdMnSb relative to Pd₂MnSb. This phenomenon, and the general shape of the curve can be understood in terms of the conduction electron polarization model developed by Blandin and Campbell.     

External field influence on the magnetic hyperfine fields in alpha-manganese

We report a study on the magnetic nature of the two hyperfine fields observed in α-Mn by PAC. Both of the field sites behave completely differently under the influence of an external field ranging from zero to 4 Tesla. The so-called high field originates from the local moment antiferromagnetism of the matrix, while the low field should be associated with an itinerant magnetism.     

Distribution of electric and magnetic hyperfine fields in Fe-rich gallo-germanates

The crystal field disorder in some tetragonal and trigonal Ca-gallo-germanates, i.e., A₂Fe₂ZO₇ and A₂LnFe₃Ge₃O₁₄, with A?=?Ba or Sr, Ln?=?La or Nd and Z?=?Ge or Si, has been studied by ⁵⁷Fe Mössbauer spectroscopy. The observed distribution of the hyperfine fields is analysed from a theoretical model based on the additive perturbation approximation of crystal fields, a rigid lattice of ionic point charges and the random substitution of Fe³⁺/Z⁴⁺ and A²⁺/Ln³⁺.     

DPAC measurement of the hyperfine fields in100RhCo and100RhFe

Using the 85–75 keV -cascade of¹⁰⁰Rh, we report the first DPAC measurement of the hyperfine field in¹⁰⁰RhCo and¹⁰⁰RhFe. Our results were made possible by continued improvement in time resolution using BaF₂ scintillators. At room temperature we obtained fields of 420.6(1.3) kG and 540.4(1.5) kG for¹⁰⁰RhCo and¹⁰⁰RhFe, respectively. The former revises an earlier spin echo result by Kontani and Itoh by 9%; the latter is consistent with the work of Matthiaset al. using resonant destruction of angular correlations.