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The electric component of microwave radiation acting on the electrons causes an alternating current which induces electron spin resonance. The oscillating part of kinetic energy of electrons is converted into Zeeman energy via Rashba magnetic field, according to oscillating electron current. Description of this energy conversion is presented and its negative contribution to the resonance signal is explained.

The Jiles–Atherton (JA) model of ferromagnetic hysteresis usually bases on the Langevin function as its anhysteretic part. This leads to a problem, since for some known materials, the anhysteretic curve may not be modeled in view of fact, that the coupling parameter $\alpha $ , as determined from their major hysteresis loop, is too large, i.e., greater than the value permissible for the Langevin function. Therefore, a new function is required in order to omit this mathematical dilemma. Here, we present a set of simple functions, with their knees depending on one parameter only. Also, a more complicated function, with knee location depending on two parameters is analyzed, however, the Brillouin function again does not solve the difficulty with $\alpha $ . Therefore, within the frame of the JA model, a new function is proposed, making possible to have the initial differential susceptibility arbitrarily small. In addition, the strengthening of the effective field is considered and the permissible values of the second coupling parameter $\beta $ , in respect to the Brillouin and Langevin functions, are presented. Finally, our new function is successfully used to model the measured anhysteretic curve.

In thin films composed of a ferromagnetic (FM) and an antiferromagnetic (AFM) layers, a unidirectional anisotropy occurs when spins at the interface of FM and AFM layers are exchange coupled. The unidirectional anisotropy is responsible for a distinctive shift of a hysteresis loop away from zero along the exciting field axis. The basic physics of FM/AFM exchange coupling remains poorly understood [1, 2]. In this work, in order to clarify the nature of FM/AFM exchange coupling we have performed temperature dependent ferromagnetic resonance (FMR) measurements on FeNi/FeMn bilayers taking into account the bilinear and biquadratic exchange coupling terms.

The problem of deriving the particle size distribution directly from superparamagnetic magnetization curves is studied by three mathematical methods: (1) least-squares deviation with regularization procedure, (2) simulated annealing and (3) genetic algorithm. Software has been developed for the latest versions of all these methods and its performance compared for various models of underlying particle size distributions (Dirac δ-like, lognormal- and Gaussian-shaped). For single peak distributions all three methods give reasonable and similar results, but for bimodal distributions the genetic algorithm is the only acceptable one. The genetic algorithm is able to recover with the same precision both the lognormal and Gaussian single and double (mixed) model distributions. The sensitivity of the genetic algorithm—the most promising method—to uncertainty of measurements was also tested; correct peak position and its half width were recovered for Gaussian distributions, when the analysed data were contaminated with noise of up to 5% of MS.

The magnetic properties of Co 68 Mn 7 Si 10 B 15 glass coated amorphous microwires of about 16.5 μm in diameter have been investigated from liquid helium up to room temperature by ferromagnetic resonance at 9.243 GHz. Based on the results of measurements both the magnetic anisotropy constants, the first arising from the stress at the interface between the metallic surface and the coating and the second one of the inner core have been obtained for the room temperature. The effective anisotropy field was determined in the range from the liquid helium to the room temperature.

In this work we report results of ferromagnetic resonance studies of a 6% 15 nm (Ga,Mn)As layer, deposited on (001)-oriented GaAs. The measurements were performed with in-plane oriented magnetic field, in the temperature range between 5K and 120K. We observe a temperature induced reorientation of the effective in-plane easy axis from [-110] to [110] direction close to the Curie temperature. The behavior of magnetization is described by anisotropy fields, H_{eff} (= 4\piM -H_{2\perp}), H_{2\parallel}, and H_{4\parallel}. In order to precisely investigate this reorientation, numerical values of anisotropy fields have been determined using powerful - but still largely unknown - interval calculations. In simulation mode this approach makes possible to find all the resonance fields for arbitrarily oriented sample, which is generally intractable analytically. In 'fitting' mode we effectively utilize full experimental information, not only those measurements performed in special, distinguished directions, to reliably estimate the values of important physical parameters as well as their uncertainties and correlations., Comment: 3 pages, 3 figures. Presented at The European Conference "Physics of Magnetism 2011" (PM'11), June 27 - July 1, 2011, Poznan, Poland

The main purpose of this paper is to promote the use of interval calculus in physics. As an example we use the system consisting of two thin films, one ferromagnetic and another one antiferromagnetic, deposited one atop of the other. We successfully and accurately simulate the positions of resonance fields of such a system, as seen in ferromagnetic resonance experiment. Interval calculations have revealed the presence of 1, 2 and sometimes even 4 distinct equilibrium configurations of the system, all corresponding to the same resonance field, when the field has a component antiparallel to that of cooling field, while only 1 such position when it points in the opposite direction. In both cases only a single resonance line is observed. As an added value we show that the exchange-biased system is in the metastable state, out of true thermodynamical equilibrium.

The specific heat of has been measured over the wide temperature range from 3.5 K to 200 K. Only one anomaly, indicating the phase transition driven by the cooperative Jahn-Teller effect, has been found, at . The phonon specific heat has been estimated and subtracted from the heat capacity measured. The Schottky anomaly originating from the population of the lowest two doublets of the dysprosium ions, and the -anomaly connected with the Jahn-Teller phase transition have been described theoretically using the molecular-field approximation. Satisfactory agreement between experimental points and theoretical dependences calculated using the material parameters known from the literature was obtained.

The results of ferromagnetic resonance (FMR) investigation of the amorphous glass-coated microwires with different internal stresses are reported. The internal stresses determine the shift of the resonance field position indicating the magnetoelastic anisotropy as the origin of the magnetic anisotropy of the wire surface region. The values of the magnetoelastic anisotropy field calculated on the basis of the theory of viscoelasticity are also presented.

Proposed is a substantially simplified, Preisach-like model for characterization of hysteretic systems, in particular magnetic systems. The main idea is to replace a two-dimensional Preisach density with just two real functions, describing in a {\em unique way} the reversible and irreversible processes. As a byproduct of our model we prove, that the major hysteresis loop alone is insufficient to produce the unique Preisach map. Keywords: magnetic hysteresis; magnetization processes; materials testing; modeling., 7 double spaced pages, 4 figures. Presented at 5th International Symposium on Hysteresis and Micromagnetic Modeling, Budapest, Hungary, May 30th - June 1st, 2005

This work is an an early stage of a larger project aiming at answering the question whether or not the Preisach map is really fingerprinting magnetic materials. More precisely, we are interested whether Preisach model of magnetic hysteresis indeed contains any physics or is just a convenient modeling tool. To this extent we study a very simple mechanical system, thus fully tractable, subjected to the external force. Despite of its simplicity, our model captures all the fundamental features of real magnetic materials, namely their hysteretic behavior, coercivity, remanent magnetization and saturation at high fields. Both the overall shape of major hysteresis loop as well as First Order Reversal Curves (FORC's) are reproduced quite correctly; they are very similar to those observed in magnetic materials. The model essentially consists of a single, spring loaded, rigid and rotative bar with non-zero friction torque. The length of a projection of this bar onto the direction of an external force is identified with magnetization. The friction torque and the spring constant are the only freely adjustable parameters of our model. Here we investigate, and present, their influence on the inferred Preisach maps., Comment: 3 pages, 6 figures, presented at The European Conference "Physics of Magnetism" (PM'11), June 27 - July 1, 2011, Poznan, Poland

An existing family of genetic algorithms, which were designed with discrete and binary variables in mind, has been extended in this paper to handle truly continuous variables. Its close relationships with Monte Carlo methods, the simplex method, simulated annealing and other direct, i.e. Derivative-free global optimization algorithms creates a really versatile tool for various difficult optimization tasks. The main area of its application should be the reconstruction of unknown, continuous, and possibly smooth, distributions of various physical quantities derived from the experimental data. Among them might be: grain-size distribution for particulate magnetic materials derived from isothermal magnetization curves, distribution of relaxation times derived from luminescence experiments or chemical kinetics (inverse Laplace transform), and other large-scale numerically hard problems. One such problem, namely solving for the grain-size distribution for particulate magnetic materials, is presented as a working example and treated in detail. Applications of this algorithm should be stable deconvolution of various spectra with a variable window and non-parametric curve smoothing with a non-smooth objective function.

Annealing of the initially amorphous Fe66Cr8Cu1Nb3Si9B13 metallic glass above its crystallization temperature leads to the ultrafine crystalline structure of the bcc-FeSi solid solution with a relatively wide distribution of the particle sizes 9≤D≤35 nm. At elevated temperatures the magnetization curves no longer show hysteresis and ideal superparamagnetic behavior is observed. The kinetics of magnetic moment increase during the crystallization process at the time of annealing is also presented.

The electron paramagnetic resonance (EPR) of Mn2+ in geometrically frustrated Mg2.97Mn0.03V2O8 single crystals is reported. The complex EPR spectrum shows resonance lines associated with two crystallographically nonequivalent lattice positions of Mn ions that are known in the kagome staircase system as "cross-tie" and "spine" sites. Additionally, strongly anisotropic resonances of various Mn2+-Mn2+ pairs are observed. The signs and values of the crystal field parameters are determined from EPR spectra. The local magnetic symmetry details of magnetic ions and components of the hyperfine structure tensor are determined for various nonequivalent manganese positions. The exchange coupling between Mn ions in "cross-tie" and "spine" sites is found to be J=41 K.

Presented is a novel, heuristic algorithm, based on fuzzy set theory, allowing for significant off-line data reduction. Given the equidistant data, the algorithm discards some points while retaining others with their original values. The fraction of original data points retained is typically 1 6 of the initial value. The reduced data set preserves all the essential features of the input curve. It is possible to reconstruct the original information to high degree of precision by means of natural cubic splines, rational cubic splines or even linear interpolation. Main fields of application should be non-linear data fitting (substantial savings in CPU time) and graphics (storage space savings).

It is shown that rapidly quenched ${\mathrm{Fe}}_{66}$${\mathrm{Cr}}_{8}$${\mathrm{CuNb}}_{3}$${\mathrm{Si}}_{13}$${\mathrm{B}}_{9}$ metallic glass, when annealed in a controlled way, shows superparamagnetic behavior at elevated temperatures. This property, as has been demonstrated, is due to the fine crystallites of the bcc-Fe(Si) solid solution created within the amorphous matrix by this annealing. Calculations performed show that the volumetric fraction of these particles is equal to 18%, and that their average dimension is as small as 10 nm. It is also shown that the single particle consists of approximately ${10}^{4}$ atoms of iron. An analysis performed allows the conclusion that the particles are chemically stable (they do not increase their volumes at the time of measurements at elevated temperatures), and that there are no interactions between them.

A numerical study of the ideal monoatomic gas in a rectangular ☐ is presented. The spatial distribution of temperature, density, pressure and chemical potential is studied in detail with and without the presence of gravitational forces. Some conclusions are drawn regarding the importance of the particle-wall interaction.

A new method for the introduction of periodic boundary conditions to the self-magnetostatic (demagnetization) tenn in micromagnetic simulations is described, using an Ewald-like summation method in real space. The long-range character of the dipolar interactions is included without any distance cut-offs. The accumulated errors are carefully monitored to provide easy control of the quality of the results. This allows the calculations to be either accurate up to floating point limitations or less precise when computational speed requirements dominate. This method is incorporated into a full micro magnetic program, and comparisons are made to analytic results.

At the very heart of the successful phenomenological model of magnetic hysteresis there is the so called Preisach distribution. In the existing literature it is implicitly assumed, that this distribution has a mirror symmetry. We show, by simple and convincing example, that this common assumption is plainly wrong. Dropping it, we gain the ability to model not only the usual hysteresis loops (major and minor) more accurately than ever before, but also those displaying the exchange bias effect, what is impossible within the framework of the symmetrical Preisach model. It is hoped, that our observation paves the way towards the unified description of all the hysteretic systems, including, but not necessarily limited to, superconductors, (multi)layered structures, nanocrystalline materials, patterned media, and - perhaps - the other non-magnetic hysteretic phenomena., 4 pages, 2 figures. Presented at the European Conference "Physics of Magnetism'05", Poznan (Poland), June 24-27, 2005. Accepted for publication in physica status solidi (b) (C) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Some recent publications on ferromagnetic resonance in amorphous wires mention presumably new kind of anisotropy, called there circumferential anisotropy, as an explanation of various spectral features. In this paper we argue that there is no special reason to speak of the new kind of anisotropy, since the observed spectra can be well described in terms of more traditional uniaxial and surface anisotropies alone., LaTex2e, 2 pages, submitted to ICM2003, Rome, July 27 - August 1, 2003

The expectation that nanocrystalline Fe-based metallic glass may show a variety of magnetic phases is confirmed experimentally. It is shown that, depending on the annealing conditions (resulting in controlled crystallite size as well as the volumetric fraction of the crystalline phase), the particles exhibit superparamagnetic or superferromagnetic behavior at temperatures above the Curie point of the amorphous matrix. At sufficiently low temperatures (around room temperature), the samples behave ferromagnetically as expected for typical nanocrystalline metallic glass. >

The novel experimental setup for measurements of magnetostriction of thin films in the temperature range starting from 4.2 K up to the room temperature, using the strain modulated ferromagnetic resonance phenomenon, is presented. The sample under investigation is fixed at the anti-node of vibrations of the longitudinal mode sapphire resonator. The resonator is excited by means of a piezoelectric transducer via the mechanical waveguide. The sapphire rod is put into a helium flow cryostat, thus allowing the measurements in the wide temperature range. The temperature gradient along the resonator length is negligible due to the very high thermal conductivity of sapphire. The setup is controlled by specially designed electronic circuit interfaced to a computer. As an illustrative example, the measurements of epitaxial Fe/GaAs(001) films were performed with in-plane magnetic field, in the temperature range between 10 K and the room temperature.

We report experimental observations of magnetic bubble domain arrays with no apparent translational symmetry. Additionally the results of comparative numerical studies are discussed. Our goal is to present experimental evidence for natural occurence of conformal structures., Comment: 7 pages, 2 figures, LaTeX2e, accepted as paper E090 at JEMS'01 (Joint European Magnetic Symposia, formerly EMMA + MRM), August 28th to September 1st, 2001, Grenoble, France

The nanocrystalline Fe66Cr8Cu1Nb3Si13B9 metallic glass with relatively low Curie temperature of the amorphous matrix has been proposed as a particulate medium showing superparamagnetic behavior at elevated temperatures. The samples of this material with different volumetric fractions of the crystalline phase, were characterized by differential thermal analysis, X-ray diffraction and transmission electron microscopy as well as by temperature dependencies of saturation magnetization and isothermal magnetization curves. The correlation between the structural parameters determined by direct measurements and those estimated from the magnetic studies is shown and discussed in terms of a new algorithm which allows to determine a distribution of the particle magnetic moments.

The expectation that the nanocrystalline Fe-based metallic glasses may show the richness of magnetic phases with a change of the temperature has experimentally been confirmed. It has been shown that, depending on the annealing conditions (resulting in controlled crystallite size as well as the volumetric fraction) the particles exhibit superparamagnetic or "superferromagnetic" behavior at elevated temperatures. In these cases, the amorphous matrix, into which the particles are embedded, is in paramagnetic state. In order to confirm the occurrence of these phases, magnetization characteristics measured at different temperatures were analyzed in terms of the well-known Langevin approach. At sufficiently low temperature (e.g., at room temperature), lower than the Curie points of both, the amorphous matrix and the particles, the sample behaves ferromagnetically in a way as it does for the typical commercial material.

An attempt is made to determine the mechanism of induced perpendicular anisotropy and magnetostriction in rf sputtered GdCo amorphous thin films. For this purpose the compositional dependences of perpendicular anisotropy and linear magnetostriction are measured and analyzed in the frame of pair ordering model. The dipolar mechanism for anisotropy and magnetostriction is extended considering anisotropic part of the RKKY interaction. It is shown that the compositional dependence of perpendicular anisotropy and linear magnetostriction can be explained if both, pure dipolar and RKKY interactions are taken into account. The performed analysis proves that the RKKY interaction plays an important role in the creation of perpendicular anisotropy and magnetostriction in sputtered GdCo amorphous films in the range of film composition investigated. Es wird der Versuch unternommen, den Mechanismus der induzierten senkrechten Anisotropie und Magnetostriktion in HF-gesputterten dunnen GdCo-Schichten zu bestimmen. Zu diesem Zweck wird die Zusammensetzungsabhangigkeit der senkrechten Anisotropie und linearen Magnetostriktion gemessen und im Rahmen des Paarordnungsmodells analysiert. Der Dipolmechanismus fur Anisotropie und Magnetostriktion wird erweitert, wobei der anisotrope Anteil der RKKY-Wechselwirkung berucksichtigt wird. Es wird gezeigt, das die Zusammensetzungsabhangigkeit der senkrechten Anisotropie und linearen Magnetostriktion erklart werden kann, wenn sowohl reine Dipol- als auch RKKY-Wechselwirkungen berucksichtigt werden. Die Analyse ergibt, das die RKKY-Wechselwirkung eine bedeutende Rolle bei der Bildung der senkrechten Anisotropie und Magnetostriktion in aufgespruhten amorphen CdCo-Schichten im untersuchten Zusammensetzungsbereich der Schichten spielt.

The static two- and four-spin correlations for the one-dimensional easy-plane Heisenberg spin system with a ferromagnetic coupling, like CsNiF3, are investigated in the classical limit by means of the transfer matrix method. They are found to consist essentially of two components which both depend exponentially on the distance between sites. Both in the high- and low-temperature regions, only one component remains and this component still dominates at intermediate temperatures. Analytic forms for the correlation functions are given for asymptotically low temperatures. These are obtained by calculating the second-frequency moment of the dynamical structure factor in three different ways, and by requiring the T=0 limit of the moment to coincide with the square of the spin wave frequency. Generalisations of the Tomita-Mashiyama recursion relations (1972) for the isotropic case are given, valid for low temperatures, Monte Carlo calculations of the correlation functions have also been performed and some results of these are presented as well.

Flux distribution in a Bi2Sr2CaCu2O8 superconductor sample, shaped as a thin disk with a hole in the center, and covered with a thin layer of magnetic garnet, was observed by means of magneto-optical Faraday effect. Applying external magnetic field perpendicularly to the sample plane with zero field cooling history, we were able to observe the flux trapped in superconductor, visible as concentric rings. Both directions of the trapped field were observed near the sample surface. Using the genetic algorithm we were able to determine the radial distribution of concentric currents in the sample under study. PACS numbers: 74.60.Ge, 74.60.Ec, 74.60.Jg