A.Z. Maksymowicz

Surface boundary conditions and angular dependence of the spin-wave resonance spectra

General surface boundary conditions with regard to the surface anisotropy energy Es(iitv, o) and changes of the static magnetization tM0 in the presurface region layer have been formulated. On the example of uniaxial surface anosotropy the influence of these factors on the angular dependence of the SWR spectrum is briefly discussed.

Angular dependence of line width in nickel platelets

Ferromagnetic resonances in nickel platelets were measured as a function of the orientation of the sample at room temperature. The line width indicates a strong dependence on the angle between the applied magnetic field and the normal to the film plane. The dependence can be well described as a sum of a constant term and a term resulting from the Gilbert type equation of motion. No spin wave resonance was observed.

Multilayer FeBSi/Si/FeBSi films - FMR experiment☆

Abstract Multilayer thin films of metallic glasses of FeBSi/Si/FeBSi alloys have been investigated by means of the ferromagnetic resonance technique. Here we measure the resonance at the x-band and in a magnetic field rotating from perpendicular orientation to the parallel case.FeBSi layers were from L =200 to 1500 A thick. The thickness t of the intermediate Si film varied in the range from 5 to 30 A. Samples were obtained by the rf sputteringtechnique. The saturation magnetization M s and g -factor were calculated from resonance positions in perpendicular and parallel cases. For t below 20 A and L less than 500 A, typical single film spectra are observed as for films with thickness equal to the total thickness of multilayer samples. For the same range of t and L > 500A there are some inhomogeneities of M s seen in the perpendicular resonance; we estimate the magnetization profile near interfaces for Δ M s =40gG. The observed linewidth of 200 to 260 G in parallel geometry is too large for inhomogeneities of M s to manifest their presence in this case. Samples with thickness t larger than 20 A of Si show a lack of the magnetic coupling and the spectra are just a superposition of roughly independent contributions from separate FeBSi layers.

Influence of inhomogenities of the magnetization and boundary conditions on spin waves spectra

Abstract A cos type form for the magnetization distribution M(z) within the sample was assumed for simplicity. The linearized equation of motion leads to the Mathieu equation for the microwave magnetization. The solutions were studied for different (in general) asymmetric boundary conditions. Both surface and volume modes appeared. The magnetization inhomogenities alter the positions of the modes and account for a mode-dependent component of the effective pinning.

Genetic algorithm approach for Ising model

Abstract The S = 1/2 Ising model for two-dimensional lattices, with nearest-neighbour interactions, is investigated using a genetic algorithm approach. Results are compared with exact analytical solutions and computer simulations. We found the genetic algorithm to be very efficient for fast search in the spin configuration phase space, especially in the early stages when the system is far from equilibrium. A combination of the genetic algorithm followed by one of the well-tested simulation techniques seems to be an optimal approach.

Penna model in migrating population – effect of environmental factor and genetics

We consider effect of possible migration between different locations on population evolution. Examples of different rules based on preferences to live in bigger or smaller populations, (or environmental capacity, or living space available), are discussed. In the limiting case of small migration intensity, each location evolves independently according to its local rules and conditions, as expected. With increasing migration, the population distribution between locations changes, including some critical behavior of extinction of population in some locations for specific set of the rules. Then the deserted location may become populated again if the migration is still on increase as a result of a pressure to move. Presented version is devoted to the migration controlled exclusively by environmental factor, yet the model is primarily designed to describe influence of other factors which may control migrating processes such as inherited mutation load, age, or other parameters associated either with individuals or the specific location, races mixing, or recovery of environmental capacity.

Biological ageing with birth rate controlled by mutations in the Penna model

Summary Within the Penna model, we assume a modification with a reproduction rate B that depends on the health state of the individual defined by the number of bad mutations. The idea is that biologically weaker individuals has got less chance to produce offsprings. The results obtained from simulations and for typical set of model parameters show that then the mortality rate q(a) is increasing faster with age a. The maximum age is also limited from about 50 percent of the biological maximum lifespan for the standard Penna model, to about 40 percent. We also conclude that bad mutation distribution r(a) is altered so that younger individuals may accommodate significantly more bad mutations, up to 25 percent, as compared with the standard model (5 percent). In summary, it makes sense to force less productivity for older and weaker individuals.

Ferromagnetic resonance in coupled permalloy double films separated by a Cu interlayer

Abstract Ferromagnetic resonance (FMR) at 16 GHz was used to study the magnetic coupling between two-layers of permalloy separated by a nonmagnetic Cu layer. Samples with the same thickness (600 A) of both permalloy layers were deposited from e-gun sources onto glass substrates in UHV. The thickness d of the Cu interlayer was varied from 5 to 37 A. The exchange coupling energy ( E = - KM 1 · M 2 ) model was used to describe the interaction between the two magnetic layers. It was found from the ferromagnetic resonance data in the perpendicular configuration that K ( d ) follows an exponential law, K = K 0 e - d / q , where q = 9.3 A .

Magnetic moments for different local atomic configurations in Fe-Cr alloys

Studies local magnetic moments in binary alloys as a function of alloy concentration. A two-sublattice model accounts also for the antiferromagnetic solutions found in the Cr-rich region. The effect of local atomic configuration is considered and the shift in atomic energy levels due to charge transfer is taken into account. The continued fractions technique is employed for calculations of the Local Green functions. The Coulomb repulsion term is treated in the alloy analogy approximation and the intra-atomic exchange term is treated by the Hartree-Fock approximation. Calculations are performed for parameters corresponding to Fe-Cr alloys. The magnetic moments of Cr and Fe agree with experimental data: ferromagnetic (up to 70 at.% Cr) and antiferromagnetic (above 83 at.% Cr) phases were found. The ferromagnetic moment of Fe decreases linearly against the number of Cr atoms in the vicinity; the rate, however, is concentration dependent. The magnetic moment of Fe in pure chromium is 1.5 mu B and Fe is antiferromagnetically coupled to Cr atoms.

Computer simulation of dynamics of surface growth

It is shown that limited surface diffusion may strongly modify properties of the film surface. For linear samples, when some analytical results are known for random deposition, the fractal dimension D of the surface is discussed. Model predictions and computer simulation shows that D < 1 for the static case, when assembly of clusters is scanned. The surface is smoother for positive binding energy between atoms, and more rough otherwise. With zero binding energy, analytical results of random growth is recovered.