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Hard Magnetic Materials
Published in David Jiles, Introduction to Magnetism and Magnetic Materials, 2015
The most commonly used hard ferrites are: (1) strontium ferrite, SrFe12O19 (SrO·6Fe2O3), used in microwave devices, recording media, magneto-optic media, telecommunication, and electronic industry; (2) barium ferrite, BaFe12O19 (BaO·6Fe2O3), used for permanent magnet applications where the need is for stability to moisture and corrosion-resistance; they are used in loudspeakers and as a magnetic recording medium, such as on magnetic stripe cards; and (3) cobalt ferrite, CoFe2O4 (CoO·Fe2O3), which is used in some media for magnetic recording and in stress sensors.
Design and Construction of Magnetic Storage Devices
Published in Bharat Bhushan, Handbook of Micro/Nano Tribology, 2020
Hirofumi Kondo, Hiroshi Takino, Hiroyuki Osaki, Norio Saito, Hiroshi Kano
Barium ferrite crystallizes in a complex hexagonal structure whose easy axis is the hexagonal axis (Figure 12.71). The interest of barium ferrite comes from the perpendicular magnetization (hexagonal axis). Potential benefits of perpendicular recording have been claimed to be the reduction of self-demagnetization and retention of sharp transitions, which might be an attractive candidate for advanced applications. However they have been slow to find commercial applications. Barium ferrite has not yet been used in products principally because of the poor dispersibility, the rather low Ms, and high price.
Transducer drive mechanisms
Published in John Borwick, Loudspeaker and Headphone Handbook, 2012
Around 1930 the telephone industry was looking for non-conductive magnetically soft materials to reduce eddy current losses in transformers. This led to the discovery of the ferrites. The most common of these is barium ferrite which is made by replacing the ferrous ion in ferrous ferrite with a barium ion. The BH product of barium ferrite is relatively poor at only about 30 kJ/m3, but it is incredibly cheap. Strontium ferrite magnets are also used. In the 1970s the price of cobalt went up by a factor of twenty because of political problems in Zaire, the principal source. This basically priced magnets using cobalt out of the mass loudspeaker market, forcing commodity speaker manufacturers to adopt ferrite. The hurried conversion to ferrite resulted in some poor magnetic circuit design, a tradition which persists to this day. Ferrite has such low Br that a large area magnet is needed. When a replacement was needed for cobalt-based magnets, most manufacturers chose to retain the same cone and coil dimensions. This meant that the ferrite magnet had to be fitted outside the coil, a suboptimal configuration creating a large leakage area. Consequently traditional ferrite loudspeakers attract anything ferrous nearby and distort the picture on CRTs. It is to be hoped that legislation regarding stray fields emitted by equipment will bring this practice to a halt in the near future. Subsequently magnet technology continued to improve, with the development of samarium cobalt magnets offering around 160 kJ/m3 and subsequently neodymium iron boron magnets offering a remarkable 280 kJ/m3. A magnet of this kind requires 10% of the volume of a ferrite magnet to provide the same field. The rare earth magnets are very powerful, but the highest energy types have a low Curie temperature which means they are restricted in operating temperature.
High-frequency absorption properties of gallium weakly doped barium hexaferrites
Published in Philosophical Magazine, 2019
S. V. Trukhanov, A. V. Trukhanov, V. G. Kostishyn, N. S. Zabeivorota, L. V. Panina, An. V. Trukhanov, V. A. Turchenko, E. L. Trukhanova, V. V. Oleynik, O. S. Yakovenko, L. Yu. Matzui, V. E. Zhivulin
The interest in research of BaFe12O19 barium ferrite of M-type with hexagonal structure and then solid solutions substituted by different diamagnetic cations (Al3+, In3+, Ga3+, Sc3+, etc.) [5–9] is caused also by their high functional properties. Excellent chemical stability and corrosion resistance [10] do them ecologically safe and suitable for application practically without restrictions in time. The combination of high coercive force (Нс ∼ 160–55 kA/m) with rather high residual induction allows to receive permanent magnets with satisfactory specific magnetic energy [11]. Their low conductivity (ρ ∼ 108 Ω cm) allows to apply hexaferrite magnets in the presence of high-frequency magnetic fields. For the first time, barium hexaferrite, isomorphic to PbO*6Fe2O3 magnetoplumbite, has been received in Philips firm [12] still in the 1950. The main magnetic, electric and structural properties of hexaferrites are discussed in the review [13].
Preparation and characterization of a new hydrophilic and biocompatible magnetic polypropylene carrier used in wastewater treatment
Published in Environmental Technology, 2018
According to the analysis of FTIR spectra and EDAX of HBMPC, it is known that magnetic material – the barium ferrite, whose major component was Fe3O4, has already been dispersed in HBMPC. The molded carrier was magnetized with a magnetizer (MZM30200, China); the magnetic induction on the surface of HBMPC was 4–6 mT. It is shown that HBMPC did have a certain weak magnetism.