Study Of Magnetic Systems Research Articles

Use of logarithmic sensitivity in power system analysis: the example of lighting circuits (hot filament, LED and fluorescent lamp circuits)

Logarithmic sensitivity characteristics were widely employed by Ch. P. Steinmetz in his classical studies of magnetic systems. In the present case, the authors deal with power sensitivity, K(U) = (dP/P)/(dU/U), where U is the amplitude (scaling factor) of the applied voltage and P is the averaged power. That such characterisation can be suitable for non-linear power systems is demonstrated for lighting systems: incandescent lamp circuits (i.e. the hot filament), LEDs and fluorescent lamp (FL) circuits. For FL circuits, the problem of minimisation of K(U) is shown to be practically and methodologically very important. On the pedagogical regard, the opinion is expressed that the described use of K(U) should be taught in basic courses of circuit theory and power systems.

Magnetic circular dichroism in soft X-ray resonant inelastic scattering

We discuss the application of resonant inelastic X-ray scattering to the study of magnetic systems in the soft X-ray range. To this end we distinguish two broad areas. In the first the layout of the experiment is such that the absorption magnetic circular dichroism (MCD) is not zero. In the second the magnetisation is perpendicular to the incident helical beam so that the absorption MCD is zero. In the first area we summarise published results on Fe-Co alloys and we present new data on Mn impurities in Ni together with calculations. In the second area we summarise published results on Ni in Ni-ferrite with final 3s shell excitation and we present new results on Co-metal and Co in Co-ferrite measured with a new approach. This is based on the incident energy dependence of the integral of the Raman spectrum in inner shell excitation (integrated resonant Raman scattering). The potentialities and the limitations of the above methods are critically presented.

The K.U. Leuven pulsed-field facility solid-state physics in high magnetic fields

The pulsed-field facility has five parallel measuring stations. Most functions of each experiment, in particular, the control of the capacitor bank, data recording and cryogenics, are controlled by a central computer which is part of a network for data processing and is linked by fiber optics to the capacitor bank and the stations. User magnets are designed to work reliably up to 50–60 T with a pulse duration of the order of 20 ms. The pulse can be extended by a crowbar circuit. The available cryogenic equipment includes flow cryostats, 4He bath cryostats, 3He bath cryostat and a 50 mK dilution refrigerator. Physical properties such as magnetization, magneto-transport phenomena, far-infrared (FIR) optical absorption and photoluminescence (PL) in the visible and near infrared can be studied. The solid-state research is focused on the following topics: the normal state transport properties of high-temperature superconductors, the study of magnetic systems as spin-Peierls compounds, Mn-Oxide GMR materials and Fe-Oxide garnet compounds, and low-dimensional semiconductors such as self-assembled quantum dots and quantum wells.

Applications of soft X-ray magnetic circular dichroism

Several recent examples of the application of soft X-ray magnetic circular dichroism (SX-MCD) in the study of magnetic systems are presented. First, the applicability and limitations of obtaining element-specific orbital and spin moments in magnetic systems via transmission MCD method are described. As an extension of this method, spin polarized L-edge extended X-ray absorption fine structure (EXAFS) of Fe, Co, and Ni films are measured. The data show the presence of a large spin dependence in the EXAFS of Fe and Co while no measurable dependence is seen for Ni, indicating significant differences between the spin-dependent scattering potentials of Fe, Co, and Ni. To further demonstrate the applicability of SX-MCD to practical systems, two dimensional magnetic hysteresis loops of a complicated trilayer system, FeCo/Mn/FeCo, are measured for each of the constituent elements. The data indicate that Mn has a net moment in this system and is strongly coupled to the enclosing FeCo layers. Furthermore, the results show unequivocally that the Mn moment is rotated from that of Fe and Co by -23/spl deg/ and this angle is largely preserved throughout the moment reversal process.

Theory of Random Magnets

Much of the enormous increase in our understanding of collective phenomena during the past few decades has arisen from the study of magnetic systems. The formulation of concepts such as universality, broken symmetry, and scaling near continuous phase transitions, as well as the development of the powerful ideas of the renormalization group, have been strongly influenced by research in magnetism. This is due in part to the availability of a host of experimentally accessible magnetic systems, and in part to the remarkable fact that simple models of magnetism capture the essential physics of the phases and ordering transitions in more complicated systems.