Charge transfer and magnetic properties in amorphous alloys of Fe with Y,Th or Zr

Various amorphous alloys of Fe with Y, Th or Zr were prepared either by melt spinning or by vapour deposition. Magnetic and electrical-transport properties were studied. The alloys are either Pauli paramagnetic or show a random antiferromagnetic behaviour. In several of them we observed a negative temperature coefficient of the electrical resistivity. The ⁵⁷Fe Mössbauer effect was utilized to study the nature of charge transfer in these alloys. Indications were obtained that charge transfer in the amorphous as well as in the crystalline materials comprises s and d electrons in amounts of comparable magnitude.     

Specific heat of superconducting Th,Sc and Th,Y alloys with Ce impurities

Measurements of the specific heat jump ΔC at the superconducting critical temperature T_c on ($\text{Th, Sc}$)Ce and ($\text{Th, Y}$)Ce Ce impurity, solid solution alloy systems indicate that the former systems obey the BCS law of corresponding states (LCS) characteristic of superconductors with non-magnetic impurities while the latter systems present deviations from the LCS linear relation between reduced parameters which are attributed to the development of localized moments at the Ce ions as the Y concentration increases.     

Effect on the magnetic properties of small substitutions of iron and copper for nickel in YNi3 and Y2Ni7 intermetallics

Measurements of magnetization in static fields up to 60 kOe and magnetic susceptibility in weak ac fields of the Y(Ni_1−x M_x)₃ and Y₂(Ni_1−x M_x)₇ intermetallics (M=Fe and Cu, x _max=0.2), as well of the specific heat of these systems for some compositions are reported. It was found that these intermetallics are ferromagnetic at low temperature, and that their spontaneous magnetizations M _s at 4.2 K and Curie temperatures T _C decrease monotonically with increasing copper concentration. The magnetic susceptibility of the Y(Ni_1−x Fe_x)₃ system with 0.06≲x≲0.2 was observed to decrease rapidly with the temperature lowered below a characteristic temperature T _s. One of possible reasons for such an anomaly is shown to be the onset in this concentration region of the reentrant spin-glass state at low temperatures. The results obtained demonstrate that the tight-binding d-band model fails to explain the evolution of the magnetic properties of YNi₃ and Y₂Ni₇ in the case of small substitutions of iron and copper for nickel. Fiz. Tverd. Tela (St. Petersburg) 39, 1828–1830 (October 1997)     

Fission of Th and U in the interaction with negative muons

Muon-induced fission of ²³²Th and ²³⁸U was studied, measuring the time correlation between stopping muons, fission events and electrons.

The measured muon lifetimes are τ_μ(²³²Th) = 77.3±0.3 ns and τ_μ(²³⁸U) = 77.1±0.2 ns. After prompt fission the muon was found to be attached predominantly to the heavy fragment with a lifetime for ²³²Th of 132±7 ns and for ²³⁸U of 134±4 ns. The probability for muon conversion was found to be a few percent per fission event.

Indications were found that the muonic shape isomer is populated in ²³⁸U when the nucleus is excited in a radiationless muonic transition.     

Evidence for a localized magnetic moment in paramagnetic α-Mn from multiplet splitting

High resolution X-ray photoemission spectra of paramagnetic α-Mn are reported. The 3s and 2s levels show considerable multiplet splitting. Analysis of the 3s splitting yields a spin S ～ 1.25, implying a magnetic moment of 2.5 μ_B, in excellent agreement with a recent susceptibility value, but larger than the neutron scattering result.     

Bulk magnetic properties of the Y2TxFe14-xB compounds,where T = Al,Ni or Co

The results of magnetic measurements performed on Y₂Fe_14-xT_xB compounds, where T = Al, Ni or Co, are presented. The Curie temperatures, saturation magnetizations, anisotropy fields and reversible coefficients of magnetization are analyzed.     

Ground states for lattices of ferromagnetic granules with dipolar magnetic interaction

The magnetic phase diagrams of 2D and 3D regular lattices formed by nonspherical single-domain ferromagnetic granules featuring a dipolar magnetic interaction are studied. The energy of a magnetic state of such systems is calculated using an approximate expression for the pair interaction of nonspherical granules. The character of the magnetic ground state of the system is determined by three geometric parameters: (i) the eccentricity of granules; (ii) the ratio of periods of the rectangular (2D) or tetragonal (3D) lattice; and (iii) the ratio of a lattice period to a granule size. In contrast to the case of lattices formed by point (or spherical) magnetic moments, in which the ground state is always antiferromagnetic or frustrated (for triangular lattices), the ground state of a 2D lattice composed of nonspherical granules can be ferromagnetic. The magnetic phase diagrams of the systems studied are constructed in the space of the above geometric parameters.     

Nature of the magnetic excitation spectrum in (Sm,Y)S: CEF effects or an exciton?

The dynamic magnetic susceptibility spectrum in a single-crystal sample of the intermediate-valence compound Sm_0.67Y_0.33S is studied by inelastic neutron scattering with neutron momentum transfer and sample temperatures varying over wide ranges. Two coupled collective modes have been found in the spectrum. Unlike the higher energy mode, whose intensity approximately follows the form factor of Sm²⁺, the lower energy mode exhibits a stronger angular dependence than could be expected from the form factor for the localized f electrons. The total intensity of the inelastic component of the magnetic response decreases with increasing temperature; this is accompanied by the appearance of a broad quasi-elastic signal of a magnetic nature at significantly lower temperatures than follows from the calculated intensities of the transitions within the excited multiplet of the Sm²⁺ ion. An analysis of the observed features allows the suggestion to be made that the fine structure of the magnetic excitation spectrum in (Sm,Y)S is associated with the formation of an exciton-like intermediate-valence state on Sm ions rather than with the crystal-electric-field effects.     

One-dimensional ising model with next-nearest-neighbour interaction in magnetic field

The exact solution for the one-dimensional Ising model with nearest-neighbour and next-nearest-neighbour interactions in an external magnetic field is obtained within the framework of the Kramers-Wannier transfer matrix. The explicit analytical expressions for thermodynamic quantities such as magnetization, magnetic susceptibility and specific heat are derived and analyzed at length as functions of temperature, magnetic field, and the signs and values of the interaction parameters.     

Stopping of slow ions in electron gas with magnetic interaction

The electronic stopping and straggling of low velocity point charge in the electron gas subjected to magnetic ordering is analysed within the linear response theory. The electrons were described by the Lindhard dielectric function ?(k,ω)$\mathrm{?}(\mathbf{k},\omega )$. The magnetic interactions were included in the model along the Stoner treatment of itinerant electrons. The effect caused by phase transition was shown to be negligible comparing to the experimental result.     

The third-order elastic moduli and pressure derivatives for AlRE (RE=Y,Pr, Nd,Tb, Dy,Ce) intermetallics with B2-structure: A first-principles study

The third-order elastic moduli and pressure derivatives of the second-order elastic constants of novel B2-type AlRE (RE=Y, Pr, Nd, Tb, Dy, Ce) intermetallics are presented from first-principles calculations. The elastic moduli are obtained from the coefficients of the polynomials from the nonlinear least-squares fitting of the energy–strain functions. The calculated second-order elastic constants of AlRE intermetallics are consistent with the previous calculations. To judge that our computational accuracy is reasonable, the calculated third-order constants of Al are compared with the available experimental data and other theoretical results and are found to have good agreements. In comparison with the theory of the linear elasticity, the third-order effects are very important with the finite strains which are lager than approximately 3.5%. Finally, the pressure derivatives have been discussed.     

Effects of pressure on magnetic interactions in the rare earth intermetallics R2Ni17

The Curie temperatures of Y₂Ni₁₇ and Dy₂Ni₁₇ were observed to vary with hydrostatic pressure at a rate of –0.44 K/kbar. The results for the compounds R₂Ni₁₇ were compared with previously reporteddT _c/dp data for R₂Co₁₇ and R₂Fe₁₇ and discussed in terms of simplified collective and localizedd-electron models. The former model suggests that R₂Ni₁₇ and R₂Co₁₇ are relatively far from the Stoner instability limit, while the compounds R₂Fe₁₇ approach very weak itinerant ferromagnetism. The slow pressure variation of the compensation temperature of Dy₂Ni₁₇, –0.03 K/kbar, was attributed to the insensitivity of the R-Ni interaction to interatomic spacing.