Vladimír Jančárik

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.

Changes of Ni-Zn Properties by Substitution of Zn With Cu and Co Ions

The effect of partial substitutions of Zn²⁺ ions with Cu²⁺ and Co²⁺ ions in Ni_0.33Zn_0.67Fe₂O₄ ferrite were investigated on magnetic properties. Fine particles of Ni_0.33Zn_0.67-xMe_x, ferrites with Me = Cu²⁺/Co²⁺ were prepared by the self-propagated combustion method. Variation of temperature dependences of the magnetic susceptibility χ(T) with composition is discussed and possible magnetic mechanism is investigated. Grain size is one of the factors determining the magnetic properties of ferrite materials. The chemical and structural changes of ferrite during substitution treatment are analyzed also using Mossbauer spectrum and SEM. Initial permeability varies with ion content x in ferrite materials, which is attributed to the variation of grain size.

Magnetic study of doped Ba ferrites prepared by citrate method

The M-type barium ferrite is doped with either Co2+-Ti4+ or Co2+-Zr4+ pairs to reduce its intrinsically high uniaxial magnetic anisotropy in order to make fine particles for magnetic recording. The magnetic parameters were investigated by magnetic measurements and the Mössbauer spectroscopy. Compounds (BaF) obtained from BaCox(Ti,Zr)x Fe12-2xO19 with 0≤x≤1.0 have been prepared by the modified citrate method with the initial ratio of Ba:Fe equal to 1:10.8. The substitution of Co - Ti or Co - Zr for Fe3+ ions affects mainly the positions 2a and 4f2. Ba ferrite with the substitution x ≈ 0.8 is promising for perpendicular recording media applications.

Magnetic comparison of BaCa and BaSr substituted hexaferrite powders

Results on magnetic studies of Ba0.5Sr0.5Fe12-2x(ZnTi)xO19 and Ba0.75Ca0.25Fe12-2x(ZnTi)xO19, where x = 0.2 to 0.6, ferromagnetic powders prepared by mechanical alloying are discussed. The structural and magnetic properties of the resulting powders were analyzed by thermo-magnetic analysis, X-ray diffraction, scanning electron microscopy, M?ssbauer spectroscopy and magnetic measurements. Curie temperature, Tc decreased dramatically (drop ~ 39%) for BaCa samples, whilst for BaSr samples remained almost without change (diminution ~ 2%) at x ? 0.2. SEM studies showed that all the particles present nearly hexagonal platelet shape.

Analysis of Selected Be-Substituted NiZn Ferrites

Polycrystalline NiZn ferrites with the chemical formula (Ni_0.3Zn_0.7)_1- <i>x</i>Be<i>x</i>Fe₂O ₄with Be substituent ion <i>x</i>=0, 0.05, 0.1, and 0.25 have been prepared by the ceramic method. The intrinsic and certain extrinsic magnetic properties such as the coercivity <i>H</i> _c, initial permeability ¿<i>i</i>and hysteresis loops of the ferrites have been measured and discussed from the point of view of the substituting element contents as well as the grain size. The MO¿ssbauer spectra of certain samples have been analysed as well. According to the requirement of specific applications the properties of NiZn, ferrite have to be improved by means of proper substitution of selected ions and processing technology.

Optimisation of amplitude distribution of magnetic Barkhausen noise

Abstract The magnetic Barkhausen noise (MBN) measurement method is a widely used non-destructive evaluation technique used for inspection of ferromagnetic materials. Besides other influences, the excitation yoke lift-off is a significant issue of this method deteriorating the measurement accuracy. In this paper, the lift-off effect is analysed mainly on grain oriented Fe-3%Si steel subjected to various heat treatment conditions. Based on investigation of relationship between the amplitude distribution of MBN and lift-off, an approach to suppress the lift-off effect is proposed. Proposed approach utilizes the digital feedback optimising the measurement based on the amplitude distribution of MBN. The results demonstrated that the approach can highly suppress the lift-off effect up to 2 mm.

Magnetic properties of Ni ferrites substituted by divalent Zn, Cu and Co ions

Substituted Ni ferrite samples with chemical composition Ni_1-x-y-zZn_xCu_yCo_zFe₂O₄, where x = 0.4, 0.5 and 0.6, y = 0.1, z = 0.01 and 0.02 were prepared by classical ceramic technology at the temperature of 1200°C. The influence of divalent Zn, Cu and Co ions substitution on the magnetic properties of spinel Ni ferrites was studied. The magnetic properties, such as the Curie temperature, coercive field, remanent magnetic flux density, hysteresis loop area as well as the amplitude and initial permeability were investigated by means of thermo-magnetic analysis and magnetisation curves measurements at low frequencies.

Contribution to laminar effects in magnetic yokes

Abstract The design of the magnetic cores of electromagnetic devices constructed from oriented materials requires knowledge of the magnetic parameters of the materials in an applied external field at arbitrary directions with respect to the easy axis. Some parameter effects that can arise in stacked cores are presented and a model for the domain structure is proposed to describe the magnetic parameters.