Advances in fine magnetic particles for high density recording

Abstract

Fine platelet particles of barium ferrite wereWe have studied the Ba-ferrite particles, which prepared by the hydrothermal precipitation technique. The were prepared by the hydrothermal precipitation magnetic properties such as magnetization, coercivity and method [9,lO]. There are some advantages in the temperature variation of the coercivity can be controlled by hydrothermal preparation : fine particles with narrow size the selection of the substitution elements. Non-stoichiometric distribution can be easily obtained. In the present paper, we Co2+-Ti4+ substitution yields the formation of the fine will report the preparation and the magnetic properties of particles, and further the replacement of Co2+ by Ni2' the Ba-ferrite particles, which are synthesized by the reduces the temperature variation degree of the coercivity. hydrothermal procedure.These fine particles are thought to be good candidates for highIn addition, fine acicular particles of metal a-Fe density recording. Furthermore, we briefly discussed on the have been considered as the other candidate for high density preparation procedure of fine a-Fe acicular particles.recording materials. We have studied the preparation of metal iron fine particles as well as Ba-ferrite particles. On some of the problems : narrowing particle size distribution, I INTRODUCTION increase in coercivity and resistance to environmental corrosion, we'll briefly present our experimental results. Magnetic iron oxide particles have been widely used in many applications such as pigments of paint, they have mechanical hardness and chemical stability. In magnetic recording media, it is well known that acicular iron oxide particles are coated on the substrate with longitudinal orientation. In t h~s configuration, the FeC136%0 and BaC1, were dissolved in distilled demagnetizing field causes instability of the remanent water, and the molar ratio of Fe3+/Ba2+ was adjusted to magnetization, as the recording density increases [l]. about 9. Some of the Fe3+ were replaced by other cations Therefore, there exists a limitation in the high density such as Co2+, Ni2+ and Ti4+ in order to inocllfy the recording of the longitudnal recording system. magnetic properties. The cationic solutions were mixedIn 1977, S. Iwasaki and Y. Nakamura reported with NaOH aqueous solution, and the alkaline suspensions the perpendicular magnetic recording system based on thin containing various amount of excess NaOH ( 3 to 9M ) were film media, in which the remanent magnetization cannot be prepared. Then the alkaline suspensions were inserted into reduced by the demagnetizing field[2]. Since then, many a stainless steel autoclave, and subjected to hydrothermal researchers have extensively studied and developed the treatment at temperature from 150 "C to 300 "C for four perpendicular recording system using thin film media of hours, followed by slow cooling to room temperature. The Co-Cr or others for high density recording [3,4]. In 1982, precipitates were separated with filtration, washed with Toshiba corporation...

Structural and magnetic transformation of monodispersed iron oxide particles in a reducing atmosphere

“…4 The only commercially significant process for the production of iron metal particles ͑MP͒ is the reduction of acicular particles of oxyhydroxides. 5,6 Silica or alumina are common elements added to the system to prevent sintering of the particles during the required heat treatment. 7,8 The recording density achievable with these magnetic particles is limited by the coercivity and particularly the distribution of coercivities or switching fields within the material, which are closely associated with the crystallochemical characteristics of the particles ͑mainly, particle size distribution, coating homogeneity, and particle microstructure͒.…”

Production of zinc ferrite in radiofrequency thermal plasma

“…spinellkristály-szerkezetű ferritekből készített anyagokat és eszközöket széles körben alkalmazzák, többek között erőművek füstgázának kéntelenítésére, katalizátorként [1], elektromos és mágneses adatrögzítő eszközök anyagaként [2,3], gázérzékelőkben .…”

Estudio comparativo de las propiedades magnéticas de ferritas hexagonales de Bario obtenidas por los métodos de coprecipitación y microemulsión

“…Para obtener los polvos de ferrita de bario por el mŽtodo de coprecipitaci-n qu'mica, se prepar-una soluci-n acuosa que contiene 60.63 gramos de nitrato fŽrrico nanohidratado (Fe(NO 3 ) 3 .9H 2 O) y 3.558 gramos de nitrato de bario…”

“…En esta aplicaci-n se requieren part'culas magnŽticas de composici-n homogŽnea, con su eje de magnetizaci-n f ‡cil perpendicular al medio de grabaci-n y capaces de resistir los altos campos desmagnetizantes que se crean. Las part'culas hexagonales de ferrita de bario, con su eje c de f ‡cil magnetizaci-n perpendicular a la cara hexagonal, resulta ser una buena opci-n (3)(4)(5). Pero la coercitividad de las part'culas hexagonales de ferrita de bario es demasiado elevada, lo cual impide una escritura exitosa por las cabezas disponibles.…”