Jean Pierre Chatelon

Unidirectional propagation of magnetostatic surface spin waves at a magnetic film surface

An analytical expression for the amplitudes of magnetostatic surface spin waves (MSSWs) propagating in opposite directions at a magnetic film surface is presented. This shows that for a given magnetic field H, it is forbidden for an independent MSSW to propagate along the direction of − H→×n→, where n→ is the surface normal. This unidirectional propagation property is confirmed by experiments with both permalloy and yttrium iron garnet films of different film thicknesses, and has implications in the design of spin-wave devices such as isolators and spin-wave diodes.

NUMERICAL STUDY OF A CIRCULATOR USING YIG THIN FILM WITH A COPLANAR STRUCTURE

This paper deals with the field of passive microwave components. Coming from the requirements of mobile communication devices, miniaturization of microwave components is needed. The DIOM laboratory is using the RF sputtering to realize magnetic thin films. The use of these magnetic thin films for a circulator design enables to develop a new manufacturing technique compatible with the miniaturization of these devices. These components are devoted to future wireless applications in the 8–12 GHz frequency range. The advantages of these components lie in using YIG thin film and in the fact that accesses to the device are coplanar waveguide (CPW). The CPW structure has a signal line and a ground in the same plane. Therefore, the circulator with a CPW structure will be easily fabricated using low cost lithography. Moreover, connections with other devices will be easier.

Determination of Initial Magnetic Permeability of YIG Thin Films Using the Current Sheet Method

Abstract. A new technique of inductive measure to determine the initial magnetic permeability (r) of Yttrium Iron Garnet (YIG) thin films has been conceived and developed in our laboratory. The magnetic material is deposited by radio-frequency sputtering between two copper thin layers on alumina substrate. Because the as-deposited films are amorphous and non magnetic, thermal annealing is necessary to make the films crystallize and to obtain satisfactory magnetic properties. After different tests considering the geometrical, morphological and magnetic properties, we have established a protocol permitting to manufacture a prototype in an original design. The performance of the fabricated micro-inductor has been checked using a physical-chemistry characterization. To obtain accurate measurements, we have used a four-point probe test bench and a precision LCR meter. The current sheet method has been validated with thick layers of commercial YIG. The results obtained for thick and thin films of YIG have been compared to the simulation and theoretical ones. Several tests, made for different thickness and different number of loops, have permitted us to evaluate the magnetic permeability of YIG thin films to 32 ± 4.

Design and Study of Interleaved and Face to Face Magnetic Microtransformers

The aim of this paper is to compare two types of microtransformers using the High Frequency Structural Simulation simulator. Interleaved and face to face transformers were studied for applications in dc/dc converters and variable speed drive. These transformers have a magnetic material core (yttrium iron garnet) and square spiral windings. The main purpose of the use of magnetic material is to increase the magnetizing inductance LF and the coupling factor k. For this, LF and k were studied by simulation as a function of turn spacing, magnetic, and insulating layer thicknesses. The results presented were compared with recently published works. An important improvement of the main properties was observed in the frequency range (10-100 MHz). The interleaved transformer properties are equal to 0.95 and 0.80 μH for k and LF parameters, which corresponds to an 0.05 μH/mm2 inductance area ratio (LF/A), whereas for the face to face transformer k and LF are equal to 0.9 and 0.78 μH for an 0.08 μH/mm 2 inductance area ratio. Interleaved transformers were manufactured and characterized. Results show close agreement between simulation and measurement results.