Jozef Sláma

Frequency dispersion of permeability in ferrite polymer composites

The permeability spectra of sintered MnZn ferrite and magnetopolymers prepared by mixing the ferrite particles with polymer have been studied. The experimental data have been compared with predictions of magnetic circuit model described for dynamic conditions. The applied model analyses the effect of the demagnetising field due to shape and size of ferrite particles.

Composite material with substituted Li ferrite for high-frequency applications

Abstract Magnetic composites using polymer polyvinylchloride (PVC) matrix and Li ferrite of chemical formula Li 0.525 Fe 1.825 Ti 0.35 Zn 0.30 O 4 (LTZF) with treated additions of MnO 2 and Bi 2 O 3 as a magnetic filler, were prepared. The substituted Li ferrite was processed by a conventional solid state reaction and the magnetic parameters, measured on the compact sintered and composite specimens, are presented. The effect of filler quantity on magnetocomposite complex permittivity and microwave absorption has been studied in X-band frequency range.

Influence of Co–Ti substitution on coercivity in Ba ferrites

Abstract Polycrystalline BaCo x Ti x Fe 12−2 x O 19 samples with 0⩽ x ⩽1.2 ions per formula units were prepared by modified citrate precursor method with the initial ratio of Ba:Fe equal to 1:10.8. The cationic site preferences of Co 2+ and Ti 4+ in Co–Ti substituted Ba ferrite were investigated by magnetic measurements and Mossbauer spectroscopy. The coercivity H c , specific magnetic polarisation J s-m ( J s-r ) and Curie temperature T c is decreasing with increasing Co–Ti substitution. The variation of these parameters can be explained by the replacement of the Fe 3+ ions in the 2b and 4f 2 sites, and by splitting the 12k site on the two magnetically non-equivalent sublattices (12k and 12k′), which reduces the effective uniaxial anisotropy of Ba ferrite.

HOPKINSON EFFECT STUDY IN SPINEL AND HEXAGONAL FERRITES

Hopkinson Effect Study in Spinel and Hexagonal Ferrites The magnetic susceptibility shows a Hopkinson peak just below the Curie temperature TC when heating the selected hexagonal and spinel ferrite samples. It is proposed that this peak can be associated with a transition from stable magnetic state to super-paramagnetic relaxation above the blocking temperature up to the TC. The Hopkinson effect results are compared with SEM micrographs of both studied hexagonal and spinel ferrites.

Analysis of Magnetic Properties of Substituted Li Ferrites

Substituted Li ferrites with chemical composition Li_0.5+0.5 <i>t</i> -0.5<i>x</i>Fe_2.5-1.5 <i>t</i>-0.5<i>x</i>Ti<i>t</i>Zn<i>x</i>O₄, where <i>x</i> = 0.20 and <i>t</i> = 0.35, 0.45, 0.55 with additions of 0.005 Bi₂O₃ and 0.05 MnO₂ were synthesized by ceramic method and from solutions of metallic salts and citric acid. The intrinsic and extrinsic magnetic properties were measured and are discussed from the point of view of the substituting element content as well as the grain size. The magnetic polarization, Curie temperature, saturation induction, susceptibility, and coercivity were measured and the Mossbauer spectra of certain samples have been analyzed. According to the requirements in specific applications, the properties of LiZnTi ferrite can be improved by means of proper substitution of selected ions and processing technology.

Magnetic permeability study of composite magnetopolymers

The aim of the work is present results of granulometry influence study on the effective permeability of composites with MnZn ferrite filler in the polymer matrix. The frequency dependencies of complex permeability components were measured and discussed with proposal model based on hysteresis and relaxation process.

The optimalization of the Ba-hexagonal ferrite phase formation

Abstract The Ba-hexagonal ferrite phase has been prepared by the citric precursor method. The decomposition of the precursor started at 360°C. The optimal Fe:Ba ratio was 10.8. The crystalline Ba-ferrite starts forming at a temperature of 600°C. Mono-phase Ba-ferrite is obtained at 950–1100°C.

Magnetic powder filled polymers

The composite magnetic materials with commercial polymer matrix along with different magnetic fillers have been studied, with the aim of tailoring their properties. The measured magnetic parameters of the prepared samples have been compared by those calculated using a model in which the magnetic powder particles are surrounded by the thin layer of matrix material. >

Preparation of substituted barium ferrite powders

Abstract Pure and (Co, Ti)-substituted Ba ferrites, produced by the citration process with the initial Fe to Ba ratio equal to 11.2, have been studied. The substitution x in Ba(Co, Ti)xFe12-xO19 has been varied from 0 to 1.1. The mechanism of the magnetic structure formation has been controlled by Mossbauer and infrared spectroscopy combined with magnetic susceptibility measurements. The substitution x = 0.5 showed promising properties for magnetic recording applications.

Mössbauer Study of Microstructure and Magnetic Properties (Co, Ni)-Zr Substituted Ba Ferrite Particles

The barium hexaferrites of M-type BaFe12−2x (Co, Ni) x Zr x O19 were synthesized by citrate precursor method in 0.0 ≤ x ≤0.6 range. For comparison, Ni-Zr compounds were also prepared by mechanical milling. Mossbauer measurements show that of Zr4+ ions have preference for 2b and 2a+4f 1 sites whereas Co2+ ions prefer 4 f 2 and 12k positions. Different occupations were observed on Ni-Zr substitutions. The temperature coefficient of the coercivity, dH c /dT, was nearby to zero (0.01 kA/m°C) for the Co-Zr substitutes and positive for the rest of the samples. A fast reduction of coercivity H c with the increase in substitution level (370 to 150 kA/m) were underwent for all (Co, Ni)-Zr mixtures.