D. Vincent

Influence of particle size distribution on the initial susceptibility of magnetic fluids in the Brown relaxation range

Abstract We present experimental results on magnetic liquids characterised by a size distribution of particles. The initial complex susceptibility has been studied in the Brown relaxation range using a polarimetric method. The position and the shape of the relaxation peak allow to determine apparent values of hydrodynamic mean diameter and its standard deviation. Theoretical calculations were made from the Debye model including the size distribution of particles and the experimental study shows its influence and the necessity to take it into account for a better results exploitation. In these conditions, the Debye model used gives excellent results in accordance with the experimental points.

Gyromagnetic resonance in ferrofluids made from manganese ferrite or magnetite particles: influence of a constant axial magnetic field

Abstract We have measured the susceptibility of two ferrofluids in the frequency range 0.1–20 GHz. We confine the liquid under test in a coaxial line cell and we use the reflection/transmission method to obtain χ ∗ . If we add a constant axial magnetic field to the microwave field we evidence an increase of the gyromagnetic resonance phenomenon appearing as a consequence of the artificial increase of anisotropy.

Magnetic Behavior of Barium Hexaferrite Nanoparticles

An analysis of the magnetic behavior of Barium Hexaferrite nanoparticles is presented in this paper. The particles’ average size is around 200 nm. The SU-8 photoresist is used as dielectric host matrix in which the particles are embedded. The volume fraction of magnetic particles reached is around 10%. Microwave characterizations show the properties of the resulting nanocomposite. The external applied magnetic field plays the main role in orienting these magnetic particles in the composite. Coplanar CPW lines were used to investigate the magnetic material’s efficiency by its non-reciprocal effects. Magnetic nanocomposites seem promising material for future applications. Thus, higher magnetic particle volume fractions and better orientation are required.

Towards the integration of barium ferrite sputtered films for coplanar isolators and circulators in the millimeter wave range

Signal processing in communication, instrumentation and radar detection requires low-cost microwave and millimeter wave devices. The integration of millimeter wave passive components like isolators and circulators is thus a major issue. In these components, the nonreciprocal nature of wave propagation in ferrites plays an essential role. Hexagonal ferrites,such as barium ferrite (BaFe12O19 or BaM), which has a large resistivity and high permeability at high frequency, are of great interest for such applications. The present work deals with the characterization of barium hexaferrite sputtered films and with the device integration for the development of coplanar isolators and circulators working at frequencies above 40 GHz. The BaM films (in the thickness range of 10μm) were deposited on alumina substrate by RF magnetron sputtering at room temperature and were then crystallized using a 800°C thermal annealing. Structural properties were evaluated by X-ray diffraction and the magnetostatic properties of the film were determined using a Vibrating Sample Magnetometer (VSM) leading to assess a range of deposition conditions appropriate for device integration. Both coplanar isolators and circulators were implemented using standard lift-off technique. Coplanar circulators were designed by analytical calculation and 3D electromagnetic simulation (HFSS) supposing a saturated material and no losses. The microwave range characterization was performed using a network analyzer and a probing system with a prior OSTL calibration. The coplanar isolators were characterized both at the remanence and under a polarizing field. At the remanence, the gyroresonance occurred at 50 GHz and the nonreciprocal effect - difference between the transmission coefficient in the forward direction and in the reverse direction - was evaluated. When applying a polarizing field, the tunability of the isolator was verified experimentally. Finally first measurements on integrated coplanar circulators are currently under progress.