Rotational and domain wall motion aftereffect in a patterned array of small particles

Aftereffect for magnetization processes by rotation and by domain wall motion was investigated on the same, single domain, two-state system of a square 2D (two-dimensional) array of garnet particles. Aftereffect measurements were performed magnetooptically. The particles are thermally stable, the particle energy is 10(-6) erg compared to the thermal energy of 10(-12) erg. No aftereffect of rotation switching of the system of "up" and "down" magnetized particles could be observed at room temperature. At increased temperatures thermally activated switching, very weakly depending on magnetic field, is observed. Each individual particle can be demagnetized into a metastable stripe domain structure. The barrier for DW (domain wall) motion is much lower than the barrier for rotation, and a significant aftereffect was measured on the same particles, demagnetized into a domain structure. The observed time dependence for DW aftereffect is exponential, M(t)/Ms=d* exp(-et), where d=0.04, and e=1/tau follows the increase of the magnetization with field, de/dH=0.021 /s/Oe

Defect related switching field reduction in small magnetic particle arrays

An array of 42 mum square, 3 mum thick garnet particles has been studied. The strong crystalline uniaxial anisotropy of these particles results in the stable remanent state being single domain with magnetization parallel to the film normal. Magneto-optic measurements of individual particles provide distribution statistics for the easy-axis switching field H-sw, and the in-plane hard-axis effective anisotropy field, H-eff, which induces the formation of a metastable stripe domain structure. Both H-sw and H-eff are much smaller than the crystalline anisotropy field. Micromagnetic simulations show that the small H-sw cannot be attributed to shape anisotropy, but is consistent with smooth, localized reductions in the crystalline anisotropy caused by defects in either the particles or the substrate

Hysteretic properties of a two dimensional array of small magnetic particles: a test-bed for the Preisach model

The magnetization process of a regular two-dimensional array of small, strongly uniaxial single domain magnetic garnet particles, groups of particles, and major loop properties of a "macroscopic" sample, has been investigated experimentally and simulated numerically. These particles correspond to the assumptions of a simple Preisach model. The switching mode is by rotation. Each particle has a square hysteresis loop, with no reversible or apparent reversible component. Requirements of wiping-out and congruency properties are satisfied. From measurements of the up- and down switching fields on individual particles, the major loop can be reconstructed, and it is shown to be in in excellent agreement with the measured one. The transition from individual to collective behavior is smooth and the properties of a system, consisting of 100 particles, correspond to the major loop behavior. The numerically simulated major hysteresis loops agree very well with the measured loops, the switching sequence and the magnetization curve for particle assembly was derived from the calculated interaction fields and found to be in a very good agreement with the measured values, demonstrating the reliability of numerical modeling. A new property, not included into the existing models, is the magnetization dependence of the standard deviation of the interaction field

Domain-wall coercivity in ferromagnetic systems with nonuniform local magnetic field

Domain-wall (DW) coercive field, H-CW, which characterizes pinning of DW's in soft magnetic materials, decreases strongly with increasing value of gradient, G, of the effective local DW-position-restoring magnetic field. Particular shapes of the dependence, H-CW(G), can be calculated from the mean energy dissipation of the DW moving over the particular profile of the DW pinning field, H-p. In this paper, H-CW(G) is calculated from a wall-pinning field, H-p, which is expressed as a stochastic function of the DW coordinate, x(DW). The wall-pinning field, H-p, is described as a Wiener-Levy stochastic process modified by two correlation lengths in such a way that H-p is stationary for large DW displacements and dH(p) /dx(DW) is well defined for small DW displacements. The computed H-CW(G) is close to a hyperbolic decrease, but it approaches finite values if G-->O and it decreases in a much steeper way than alpha 1/G for high values of G, which agrees with the experimental observations. Experimentally, the dependence H-CW(G) was measured on close-packed arrays of cylindrical bubble domains in two thin films of magnetic garnets, where the local field gradient, G, was controlled within the range 10(9)-10(10) A/m(2) by changing distances between neighboring DW's. The DW coercive field, H-CW, extrapolated from the measured values for G-->O was close to 80 A/m for both samples, while H-CW(G approximate to 10(10) A/m(2)) was several times smaller. Fitting the calculated H-CW(G) dependence to the experimental data, we obtained values of the Wiener-Levy correlation lengths well comparable to the DW width parameters

Cycles of Economic and Technological Change in Latecomer Aerospace Industries = A gazdasági és technológiai változás ciklusai a repülőgépgyártás későn jövőinek tükrében

This dissertation aims to describe and explain the forces behind catch-up and eventual changes in industrial leadership through the case of the aircraft industry. It addresses the long-term transformation of developing countries intro advanced industrialized ones and the entry and catch-up of latecomer companies. Such processes bring about a change in the global distribution of labour, in the interdependence of economies, expand and deepen technological capabilities of the world, and reshuffles centers of global political power. The aircraft industry lies at the center of these processes in all its aspects: it is a capital- and knowledge-intensive, strategic sector, characterised by high value added and high incomes (Prencipe, 2013). The investigation relies on various strands of literature: on the seminal works addressing latecomer industrialization and the role of the state in this process, and on neo-Schumpeterian studies of technological change and innovation

Big and little Lipschitz one sets

Given a continuous function $f: {{\mathbb R}}\to {{\mathbb R}}$ we denote the so-called "big Lip" and "little lip" functions by ${{\mathrm {Lip}}} f$ and ${{\mathrm {lip}}} f$ respectively}. In this paper we are interested in the following question. Given a set $E {\subset} {{\mathbb R}}$ is it possible to find a continuous function $f$ such that ${{\mathrm {lip}}} f=\mathbf{1}_E$ or ${{\mathrm {Lip}}} f=\mathbf{1}_E$? For monotone continuous functions we provide the rather straightforward answer. For arbitrary continuous functions the answer is much more difficult to find. We introduce the concept of uniform density type (UDT) and show that if $E$ is $G_\delta$ and UDT then there exists a continuous function $f$ satisfying ${{\mathrm {Lip}}} f =\mathbf{1}_E$, that is, $E$ is a ${{\mathrm {Lip}}} 1$ set. In the other direction we show that every ${{\mathrm {Lip}}} 1$ set is $G_\delta$ and weakly dense. We also show that the converse of this statement is not true, namely that there exist weakly dense $G_{{\delta}}$ sets which are not ${{\mathrm {Lip}}} 1$. We say that a set $E\subset \mathbb{R}$ is ${{\mathrm {lip}}} 1$ if there is a continuous function $f$ such that ${{\mathrm {lip}}} f=\mathbf{1}_E$. We introduce the concept of strongly one-sided density and show that every ${{\mathrm {lip}}} 1$ set is a strongly one-sided dense $F_\sigma$ set.Comment: This is the final preprint version accepted to appear in European Journal of Mathematic