Table I. Magnetic properties of BaFe12-2xM1xM2x019 particulates

B a F e 1 2 - ~ ~ M l ~ M 2 ~ 0 1 9 PARTICULATES GROWN FROM A GFeQQH PRECURSOR BY A FLUX METHOD (MI: CoiZn, M2: Sn/Sb)

Tsung-Shune Chin, Ming-Cheng Deng and Sung-Lin Hsu Department of Materials Science and Engineering

Tsing Hua University, Hsinchu, 300, Taiwan, Republic of China

Introduction

Barium ferrite (BF) particulates are attractive magnetic recording media for longitudinal and perpendicular recordingpurposes [1-3]. Among many preparation techniques is the flux method in which precipitates of amolphous Ba- and Fe-hydroides or/and carbonates are calcined in a flux such as KCVNaCI. In this study, BF particulates doped with (Co,Sn), (Co,Sb), (Zn,Sn) or (Zn,Sb) have been obtained by the flux method with 6-FeOOH as the precursor.

Experimental

An aqueous solution containing BaCI2, FeClz (with [Fe++]/[Ba++] = 6 - IO) and chlorides of the dopant ions was mixed with an aqueous solutlon containing NaOH (with [Naf]=[Cl-]) and extra NaCl to adjust the flux ratio (weight ratio of NaCl to the nominal BF). The mixture was heated to dry the water, during drying air was introduced at 40 - 80°C to precipitate 6-FeOOH. The dried mix- ture was then pulverized and compacted by a hydraulic press to pellets and calcined at 650 to 95OoC for 0.1 to 8 hours. The pellets were then cooled, crushed and immersed in water to remove the residual salt. Fine particulates were thus obtained by drying. VSM, x-ray diffractometer and TEM were used to study magnetic properties, phase and particle size and shape, respectively.

Results and Discussion

After drying the solution mixture, platelet 6-FeOOH phase was obtained, Figs 1 and 2. The 6-FeOOH starts to decompose at around 600 - 65OoC accompanied by the formation of BF phase, while after 850OC only BF phase can be identified for as short as 0.5 hour. The size of the BF, 20 to 400 nm can be controlled by the flux ratio rather than temperature Dopants can be easily incorporated into the BF lattice by this method, leading to promising magnetic properties shown in Table 1. It was found that the reaction temperature and time are greatly increased due to the doping. However, the doping lowers coercivity to be acceptable and also reduces particle size. Those doped with (Zn,Sn) or (Co,Sn) are the most promising, leading to a saturation magnetization of 60 to 65 emw'g, a coercivity of 800 to 900 Oe (for x= OS), and a particle size of 30 to 250 nm. A TEM micrograph of a (Co,Sn) doped particulate is shown in Fig.3.

References [ 11 D.E. Speliotis, IEEE Trans Magn., MAG-25, 4048 (1989). 123 0. Kubo, T. Ida and H. Yokoyania, IEEE Trans Magn., MAG-18, 1 I22 (1982). [3] T. Fujiwara, IEEE Trans. Magn., MAG-23, 3 125 (1987).

*Work supported by the National Science Council of the Rep. of China under grant No. NSC 8 1-0416- E007- 05/06 and NSC 81-020%E007-08.

MlXMZx Calcining Hc(0e) Ms(emu/g) Mr(emdg)

nil

Co,Sn x= 0.25 x= 0.5 x= 0.5 x= 0.5

Co,Sb x= 0.75 Zn,Sn x= 0.5

x= 0.5

850°cx 0.25hr 85OOCx 1 hrs 95OOCx 4 hrs

950OCx 4 hrs 900OCx 4 hrs 85OoCx 4 hrs 950OCx 4 hrs 85OOCx 4 hrs

90OoCx 4 hrs

2800 3000 2700 650 850 850 420 900 825

66.1 34.2 69 6 36.3 69.9 35.2 68.9 25.8 63.1 26.9 59.4 25.5 55.0 22.2 60.0 24.6 63.0 25.6

za 00 JCI a a 4 0 0a s a . 0 a 60 0 0 7 0 a a 29

Fig. 1 X-ray diffraction pattern of a dried solution mixture showing 6-FeOOH phase (Cu K,J

Fig. 2 A TEM micrograph of a dried solution mixture showing platelet 6-FeOOH phase (left) Fig. 3 A TEM micrograph of a (Co,Sn) doped particulate (right)

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