Qifan Li

Ferromagnetic resonance induced large microwave magnetodielectric effect in cerium doped Y 3 Fe 5 O 12 ferrites

In recent years, multifunctional materials contained simultaneous ferroelectric and ferromagnetic ordering have been realized. Here, a real time room temperature adaptive materials system, which demonstrates an RF magnetodielectric (MD) response, i.e., CexY3−xFe5O12 (x = 0, 0.05, 0.1, 0.15, 0.2), is reported. The magnetic and dielectric properties of Ce-doped YIG microwave ferrites processed by a traditional ceramic route have been measured over a frequency range of 4–8 GHz (C-band). The substitution of Ce not only enhances the microwave electromagnetic properties of the YIG, but also modulates the magnetodielectric response. The maximum magnetodielectric response in Ce-doped YIG sample ranges in magnitude from approximately +5% to −5% under an applied field of 1.78 kOe. This effect was attributed to electron fluctuations on the Fe cation sites. Furthermore, the magnitude of the MD response was shown to be enhanced by the cerium content. It is believed that research of the magnetodielectric effect in YIG ferrites is of great importance to the development of next generation multifunctional adaptive microwave materials, devices and integrated circuits.

High frequency permeability and permittivity spectra of BiFeO3/(CoTi)-BaM ferrite composites

Low magnetic loss ferrite composites consisting of Ba(CoTi)1.2Fe9.6O19 and BiFeO3 (BFO) ferrite were investigated for permeability, permittivity, and high frequency losses at 10 MHz–1 GHz. The phase fraction of BiFeO3 was quantitatively analyzed by X-ray diffraction measurements. An effective medium approach was employed to predict the effective permeability and permittivity for the ferrite composites, which was found to be in good agreement with experimental data. The experiment demonstrated low magnetic losses (<0.128), modified by BFO phase fraction, while retaining high permeability (∼10.86) at 300 MHz. More importantly, the BFO phase resulted in a reduction of magnetic loss by 32%, as BFO phase increased from 2.7 vol. % to 12.6 vol. %. The effect of BFO phase on magnetic and dielectric properties revealed great potential for use in the miniaturization of high efficiency antennas.

Magnetic Spectra and Richter Aftereffect Relaxation in Zirconium-Doped Yttrium Iron Garnet Ferrites

The magnetic property and the magnetic aftereffect relaxation of zirconium (Zr)-doped yttrium iron garnet (YIG) Y3Fe(5-x)ZrxO12+x/2 (x=0 and 0.1) have been investigated. The ferrites were fabricated by the traditional solid-state reaction method. A crystalline structure and an elemental spectrum analysis were identified by powder X-ray diffraction and using X-ray photoelectron spectroscopy, respectively. Both of the ferrite samples reveal a single-phase garnet structure, but show a visible difference in permeability spectra between the two samples over a frequency of 1 MHz-1 GHz. It is verified that the Zr-doped YIG ferrite contains the contribution of Richter aftereffect relaxation to magnetic spectrum due to the existence of Fe2+ ions. The fitting of the permeability spectra in terms of the Richter model is in agreement with experimental data, which successfully accounts for the causes of magnetic losses observed at 1 MHz-1 GHz for the Zr-doped YIG ferrite.