J.A. Morkowski

Spin wave spectrum and magnetization of ferromagnetic modulated films

Abstract A system of localized spins interacting by periodically modulated exchange interaction is considered. The spin wave spectrum is determined by solving numerically equations of motion for the magnon Green function. The magnon densities of states projected on the direction of modulation and the total 3-d one are calculated. Results are applied to calculate the low temperature dependence of magnetization. The Bloch law of magnetization is obeyed by the model with coefficients weakly depending on the modulation wave vector.

Electronic band structure and the X-ray photoemission spectrum of UCu5In

Abstract The family of compounds UCu5M (M ≡ Al, In or Sn) is characterized by the coexistence of magnetic order (antiferromagnetic for M ≡ Al and In; ferri-magnetic for M ≡ Sn) and Kondo lattice effects, by moderate electronic specific heat enhancement (γ/γ0 ≈ 8 for Al; γ/γ0 ≈ 11 for both In and Sn) and possibly a mixed-valence ground state. The electronic band structure was calculated by the tight-binding linear muffin-tin orbital method in the atomic sphere approximation. The electronic structure of UCu5In not unexpectedly shows marked similarities to the electronic structure of the other compounds of the family. The valence band, having a width of about 6eV, is due to prevalent contributions from the Cu 3d and U 5f electrons; the peak from the 5f electrons is situated just above the Fermi level. The X-ray photoemission spectra were taken in vacuum of 5 × 10−10 Torr from the sample surface prepared in situ. Satisfactory agreement between the measured spectrum and that obtained from the calculated electronic structure has been achieved.

Dense Kondo compound UCu5Sn - electronic structure and x-ray photoemission

The electronic structure of the paramagnetic phase of the dense Kondo, moderate heavy-fermion compound UCu5Sn was studied by x-ray photoemission and by calculations. The band structure was calculated using the tight-binding linear muffin-tin orbital method in the atomic sphere approximation. The calculated x-ray spectrum is in reasonable agreement with the experimental one. The electronic specific heat enhancement factor is γ/γ0≈11, pointing out the essential role played by the Kondo-type many-body interactions. A complex satellite structure of the core 4f spectrum from U is an indication of a possibly mixed valence state of uranium in UCu5Sn.

Phase diagram of the metamagnetic FeRh

Abstract The band structure of FeRh was calculated by the self-consistent spin-polarized linear muffin-tin orbitals method in the atomic sphere approximation (LMTO-ASA). The band structure computations were performed for ferromagnetic, antiferromagnetic and paramagnetic phases, respectively, for an applied hydrostatic pressure p . Total energy of the system was calculated for finite temperatures and the phase diagram on the plane ( T , p ) was determined. Magnetic and elastic properties of the system were analyzed. Results are compared with experimental data. The observed change of the lattice constant at the first-order transition from the antiferromagnetic to the ferromagnetic phase is confirmed.

A mechanism of an additional damping of the ferromagnetic resonance near the curie point in dilute ferromagnetic alloys

Abstract A damping of the ferromagnetic resonance in dilute ferromagnetic alloys due to fluctuations in the local concentration is discussed. A highly simplified method for calculating this additional damping is adopted : the alloy is considered as being divided into small regions, with concentration constant inside the regions, but varying slightly from region to region, and the contribution to the resonance line-width determined by scattering of magnon-like excitations on boundaries of these regions is calculated. The mechanism proposed qualitatively accounts for the observed maximum of the resonance line-width at the Curie temperature.

Spin wave stiffness constant in intinerant electron ferromagnetic alloys (invited)

A method of calculating the spin wave stiffness constant in itinerant electron ferromagnetic alloys is presented. The method is based on an effective magnon Hamiltonian derived in RPA and takes into account the magnon scattering contribution to the stiffness constant which is generally neglected in the existing quantitative estimates. The Hasegawa and Kanamori model of alloys is used, in the case of diluted alloys the model is generalized to take into account disorder in the hopping terms. The magnon energy is calculated by a perturbation method, contributions from single‐site scattering to all orders are included. For concentrated alloys an alternative procedure based on CPA is also used. Results of calculations of the spin‐wave stiffness constant for f.c.c NiFe, NiCo an b.c.c. FeNi alloys are presented.

Two-hole states in square lattice antiferromagnet

Abstract Two-holes states in two-dimensional square lattice antiferromagnets described by the t–J model are considered. In the self-consistent Born approximation for J/t E 2 ( k , k ) is higher than the sum of single hole energies, E 1 ( k )+E 1 ( k′ ) for any k , k′ implying non-existence of bound states.

Magnetic properties of ZrZn2 calculated by the functional integral method

Abstract The functional integral method based upon the Stratonovitch-Hubbard transformation is used to calculate the temperature dependence of magnetization, amplitude of the local moment, paramagnetic susceptibility and specific heat of the weak itinerant ferromagnet ZrZn 2 . Calculations are performed within the static approximation, using the alloy-analogy approximation and single-site CPA.

The multiband Hubbard model in the functional integral method; application to nickel

Abstract The method based on the Stratonovitch-Hubbard transformation is considered. Magnetic and thermodynamic properties of nickel, i.e. magnetization, the amplitude of the local magnetic moment, entropy and heat capacity as functions of temperature are studied with use of the static approximation, the alloy-analogy approximation and the single-site CPA in the functional integral method. The role of the interband exchange interaction is studied in detail. It is shown that the Curie temperature is reduced in comparison with the models without interband interactions.

Magnon-assisted transport in 2D antiferromagnets

Abstract Two-dimensional spin ½ antiferromagnets with a small concentration of holes are described by the t-t′-J model at nearly half-filling. The concept of spin-charge separation is used and the constraints on the correlated motions of holes in the strong-coupling regime are rigorously implemented. The linear spin wave approximation is assumed and the methods of the magnetic polaron theory are employed. One-magnon processes are taken into account.