Khabat Ebnabbasi

Converse magnetoelectric experiments on a room-temperature spirally ordered hexaferrite

Experiments have been performed to measure magnetoelectric properties of room temperature spirally ordered Sr3Co2Fe24O41 hexaferrite slabs. The measured properties include the magnetic permeability, the magnetization and the strain all as a function of the electric field E and the magnetic intensity H. The material hexaferrite Sr3Co2Fe24O41 exhibits broken symmetries for both time reversal and parity. The product of the two symmetries remains unbroken. This is the central feature of these magnetoelectric materials. A simple physical model is proposed to explain the magnetoelectric effect in these materials.

Taper Design of Vivaldi and Co-Planar Tapered Slot Antenna (TSA) by Chebyshev Transformer

A new method for the flares opening rate for a single radiator tapered slot antenna (TSA) is presented. A stepped quarter-wave Chebyshev transformer is calculated to minimize the frequency domain reflection and maximize the power transfer gain. Then slot widths are computed to match the Chebychev design, and smooth curves are fit to the computed steps. Different smoothing functions are compared, including the conventional exponential function, as well as cubic spline and Gaussian. The validity of the method is verified through simulations and measurements of experimental designs for the 1 to 3 GHz frequency range. In this work the TSA is fabricated on one side of a single layer Duroid substrate with dielectric constant 6.15. Although the Chebyshev transformer is an old concept, the novelty of this method is applying the transformer to design the TSA slotline taper profile, leading to a closed design procedure rather than an optimization. Advantages of this novel method are the straightforward mathematics of the design and that a simple simulation program can be written in a short time.

First observation of magnetoelectric effect in M-type hexaferrite thin films

The magnetoelectric (ME) effect in M-type hexaferrite thin films is reported. Prior to this work, the ME effect in hexaferrite materials was observed only in bulk polycrystalline materials. Thin films of SrCo2Ti2Fe8O19 were grown on sapphire (0001) using pulsed laser deposition. The thin films were characterized by X-ray diffractometer, scanning electron microscope, energy-dispersive spectroscopy, vibrating sample magnetometer, and ferromagnetic resonance. We measured saturation magnetization of 1250 G, g-factor of 2.66, and coercive field of 20 Oe for these magnetoelectric M-type hexaferrite thin films. The magnetoelectric effect was confirmed by monitoring the change rate in remanence magnetization with the application of DC voltage at room temperature and it gave rise to changes in remanence in the order of 12.8% with the application of only 1 V (DC voltage). We deduced a magnetoelectric coupling, α, of 6.07 × 10−9 s m–1 in SrCo2Ti2Fe8O19 thin films.The magnetoelectric (ME) effect in M-type hexaferrite thin films is reported. Prior to this work, the ME effect in hexaferrite materials was observed only in bulk polycrystalline materials. Thin films of SrCo2Ti2Fe8O19 were grown on sapphire (0001) using pulsed laser deposition. The thin films were characterized by X-ray diffractometer, scanning electron microscope, energy-dispersive spectroscopy, vibrating sample magnetometer, and ferromagnetic resonance. We measured saturation magnetization of 1250 G, g-factor of 2.66, and coercive field of 20 Oe for these magnetoelectric M-type hexaferrite thin films. The magnetoelectric effect was confirmed by monitoring the change rate in remanence magnetization with the application of DC voltage at room temperature and it gave rise to changes in remanence in the order of 12.8% with the application of only 1 V (DC voltage). We deduced a magnetoelectric coupling, α, of 6.07 × 10−9 s m–1 in SrCo2Ti2Fe8O19 thin films.

Room temperature magnetoelectric effects in bulk poly-crystalline materials of M- and Z-type hexaferrites

The converse magnetoelectric effect in poly-crystalline Z-type, Sr3Co2Fe24O41, and M-type, SrCo2Ti2Fe8O19 (SCTFO), hexaferrite materials are reported. The change in remanent magnetization (Mr) for M-SCTFO sintered in oxygen and sintered in air is similar and approximately equals to ∼3% in 13 kV/cm electric field and for Z-type is ∼12% in ∼10 kV/cm electric field. The measured magnetoelectric coupling coefficient, α, values at room temperature for Z-type and M-type hexaferrites sintered in O2 were measured to be 7.6 × 10−10  sm−1 and 2.4 × 10−10  sm−1, respectively. Sintering the M-type in air reduced to 1.7 × 10−10  sm−1. As it is well known, lack of oxygen in local oxygen sites implies lower resistivity and a modified magnetic structures or state. However, in magnetoelectric hexaferrites, there is an additional effect due to lack of oxygen, and the spin spiral configuration is significantly modified to lower the induced magnetization upon the application of a DC voltage or electric field.

Magnetoelectric effects at microwave frequencies on Z-type hexaferrite

Converse microwave measurements have been performed to measure magnetoelectric effects at room temperature on Sr3Co2Fe24O41 hexaferrite slabs. The measured properties include the magnetic permeability and strain as a function of the electric field E. In this paper, the microwave permeability changes are due to the application of a DC voltage affecting the static magnetization rather than shifts in ferromagnetic resonance. We conclude that when an electric field is turned on the ferrite exhibits broken symmetries for time reversal and parity.

Magneto-electric effects on Sr Z-type hexaferrite at room temperature

In this paper, magnetoelectric effects of Sr Z-type hexaferrite, Sr3Fe24Co2O41, at room temperature is measured. The change in remanence magnetization was measured by applying a DC voltage or electric field across a slab of hexaferrite. Changes of ∼18% in remanence was observed in an electric field of 10 000 V/cm implying a similar change in the microwave permeability at frequencies below 3 GHz. Also, a change in dielectric constant at 1 GHz of ∼16% in a magnetic field of only 320 Oe was measured. In these types of measurements high resistivity is critical in order to reduce current flow in the hexaferrite. The resistivity of the hexaferrite was raised to 4.28 × 108 Ω-cm by annealing under oxygen pressure. The measurements indicate that indeed electric polarization and magnetization changes were induced by the application of magnetic and electric fields, respectively. The implications for microwave applications appear to be very promising at room temperature.

Strong magnetoelectric coupling in hexaferrites at room temperature

In this paper, the magnetoelectric effect in single-crystalline Sr Z-type hexaferrite materials is reported. The measurements include material characterization and change in remanence magnetization (Mr) versus electric field. In a very low electric field equal to 3.75 V/cm, 14% change in Mr was observed. We deduced a magneto-electric coupling of 55.4 in CGS units or 2.32 × 10−6 sm−1 (SI units) which is the highest value measured to date.

In-Situ Deposition of C-Axis Oriented Barium Ferrite Films for Microwave Applications

We report the deposition of M-type films by the alternating target laser ablation deposition using Fe₂O₃ and BaFe₄O₇ targets to simulate the unit cell of BaFe₁₂O₁₉ rather than a previous used tridymite structure, such as BaFe₂O₄ for R-block. In fact, the natural composition of the R-block is easier to be simulated by BaFe₄O₇. This target provides a flexible control over magnetic properties of the deposited films. Magnetic, electrical, and structural properties were measured using both types of targets in simulating barium ferrite. The films are consistent with bulk properties of barium ferrite. However, the use of BaFe₄O₇ targets improved resistivity of the films.

Coaxial Line Technique to Measure Constitutive Parameters in Magnetoelectric Ferrite Materials

In this letter, a technique is presented to measure the constitutive parameters of magnetoelectric ferrite materials in the presence of high dc voltages. The traditional coaxial line design has been modified in a manner that it allows for the introduction of high dc voltage (≤ 1000 V) and also it minimizes electromagnetic radiation loss via connections to the magnetoelectric sample. The modified coaxial line is verified through the theoretical calculation and experimental measurements for 50 MHz to 3 GHz frequency range.

UWB Performance of Coplanar Tapered Slot Antennas

The ultrawideband (UWB) performance and impulse response parameters of tapered slot antennas with different flares opening rates and taper types fit to a stepped quarter-wave Chebyshev transformer are presented. This transformer is used to maximize the impedance bandwidth and power transfer gain. Different smoothing tapers are used to optimize impulse response parameters. The antennas were designed for 1-3 GHz frequency range, and the substrate is Duroid with a dielectric constant 6.15.