Magnetic Pigments Research Articles

Hexagonal Ferrites from Melts and Aqueous Solutions, Magnetic Recording Materials

AbstractOwing to their particular crystallographic properties, ferrimagnetic hexagonal ferrites exhibit a far greater coercive force than the conventional magnetic pigments. They therefore appear to be suitable for use in magnetic information storage procedures, some of which are novel and are at the development stage. Thus, magnetic tapes of high coercive force containing barium ferrite could be used as master tapes for copying magnetic information or for producing forgery‐proof magnetic cards, if magnetic heads having high‐order write fields were successfully developed. Moreover, platelet‐like ferrite pigments in which the preferred direction of magnetic orientation is perpendicular to the plane of the platelet are of great interest for perpendicular magnetic recording.In this progress report, the crystal structures, magnetic characteristics of hexagonal ferrites, and chemical processes for their production are discussed. In particular, reactions in salt melts or under hydrothermal conditions produce finely divided pigments whose particles have a pronounced hexagonal, plate‐like habit, a narrow particle size distribution, and advantageous magnetic properties. The magnetic properties of the pigments crystallized from salt melts may be adjusted by cation exchange.

Recording tapes using iron nitride fine powder

Magnetic recording pigment of Fe 4 N particles was prepared by nitrogenizing acicular metal iron powder. The treatment to obtain stoichiometric Fe 4 N was carried out at 400°C for 3 hours in NH 3 -H 2 (3:1) mixed gas. The saturation magnetization and coercive force were 120 emu/g and 700 Oe respectively. The Curie point of the powder coincided well with that of bulk material. Test tapes were prepared with this Fe 4 N powder. The remanent magnetic flux density (Br) of the tape was 2200 G and the coercive force was 670 Oe. From test immersion in saline solution, it is confirmed that the chemical stability of the Fe 4 N tape is superior to the Fe 4 N tape is superior to the metal tape.

Developments in the Field of Inorganic Pigments

AbstractThe specific properties of inorganic pigments result from an interplay of solid‐state properties, particle size, and particle shape. However, phenomena occurring at the pigment interfaces also have implications for the use of the pigment. The interrelations for individual classes of pigments are indicated, and two selected examples, namely transparent colored pigments and magnetic pigments, are subsequently discussed with particular attention being paid to industrial developments.

Magnetostriction and stress-induced playback loss in magnetic tapes

A direct correspondence between magnetic tape playback level, stress-induced remanence loss, and magnetostrictive properties of corresponding magnetic oxides has been observed. From these results the amount of playback loss was estimated by stressing a short segment of tape, by measuring magnetostriction in compacts of magnetic pigments or by an analysis of the Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> and Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> content if the state of the cobalt within each particle is known.

Surface Pigment Volume Concentration changes with pigment loading for particulate magnetic tape

The Surface Magnetic Pigment Concentration (SPVC) is measured by XPS analysis to a depth of 50A° and compared to the calculated bulk Pigment Volume Concentration (PVC) of particulate magnetic tape. To obtain the required resolution, a modified Van Cittert Algorithm is used to deconvolute the initial X-ray photoelectron spectra. The SPVC is obtained from the intensity of the O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1S</inf> ratio of the metal oxide to polymer oxygen, as well as from the ratio of intensity of the metal core electron peak to the polymeric C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1S</inf> peak. The two magnetic pigments studied are acicular ferro magnetic CrO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and acicular ferri magnetic ΓFe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> in a polyester-urethane binder. All particulate tape surfaces analyzed were calendered.

Effect of Inter-Particle Sintering on the Microstructure of γ Fe2O3

The use of γ Fe2O3 as a magnetic recording pigment is well known. Most commonly it is prepared by dehydration of the ∝ FeOOH to ∝ Fe2O3, reduction of ∝ Fe2O3 in hydrogen or other reducing gas to Fe3O4 and finally oxidation of the Fe3O4 to γ Fe2O3.Because of the known influence of grain boundaries on magnetic domains, a knowledge of the microstructure of the individual magnetic particles is important in theoretical considerations of switching mechanisms. Literature references disagree on the microstructure of γ Fe2O3. Some investigators claim the individual particles are essentially single crystalline ; others claim the particles are polycrystalline. In the present work, we have found no evidence that sub-grains are nucleated during the structural transformations of ∝ Fe2O3 to γ Fe2O3. Rather we have found that the single crystalline character of the starting ∝ FeOOH is preserved through the conversion to γ Fe2O3.