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환원처리가 Ba - ferrite의 물성에 미치는 영향
홍양기(Y. K. Hong),정홍식(H. S. Jung),김현준(H. J. Kim) 한국자기학회 1997 韓國磁氣學會誌 Vol.7 No.1
Physical and magnetic behaviors of reduced Co-Zn-Ti-Sn substituted Ba-ferrite particles with hydrogen are different from those of reduced-pure Ba-ferrite particles. The coercivity of substituted Ba-ferrite particles shows a peaking effect with the reduction temperature ranging from 250 to 520℃, while the coercivity of pure Ba-ferrite decreases monotonically. The reduction process of substituted Ba-ferrite has been found to be devided into three steps. At the first and second steps, the magneto-plumbite structure maintained. When the reduced-substituted Ba-ferrite particles are reoxidized, the coercivity is reversible at the first step but irreversible at the second step. During the third step of reduction process above 410℃, the magneto-plumbite structure was collapsed with formation of α-Fe and BaFeO_(3-x) phases and consequently the coercivity distribution is broaden and the coercivity irreversible. The coercivity and saturation magnetization decreases and increases up to 130 emu/g respectively. In this study, it is found that the substituted elements prevent the magneto-plumbite structure from collapse during the reduction process and furthermore migrate from the magnetic sites of 2a+4f_Ⅳ, 2b, and 12k to 4f_Ⅵ and 12k'. An increase in the coercivity before the collapse of magneto-plumbite structure is attributed to the migration of cations in hexagonal Ba-ferrite structure.
홍양기(Y. K. Hong),박상준(S. J. Park),정홍식(H. S. Jung) 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.3
Both manufacturing parameters and particles' chemical composition controll coercivity and its distribution of magnetic particles. The coercivity and its distribution are important properties for high density magnetic recording, so these are used as tool for evaluation of reproducibility of magnetic particles. We report in this paper the applications of dM / dH versus H curve, which is derived from magnetic hysteresis loop, to the evaluation of coercivity distribution of magnetic particles and oxidation studies of recording metal particles. The coercivity distribution can be estimated from the full width half maximum (FWHM) and the peak shape of the dM / dH versus H curve. The peak shape of the curve depends upon distribution of particles' coercivity. The peak of dM / dH versus H curve becomes broad and lor is splitted into two or more peaks. It depends on uniformity of particles' coercivity. When the coercivity difference between Ba-Ferrite and γ-Fe₂O₃ is larger than 600 Oe, the peak becomes broad and is consequently splitted into two peaks. Ununiformly substituted Ba-Ferrite particles show broad peak. It is apparent that the analysis of the curve is one of sensitive measuring techniques for determination of coercivity distribution and studies on magnetic properties of substituted Ba - Ferrite and oxidation of magnetic recording metal particles.
입자간 Stacking이 자기기록용 Ba - ferrite 분말의 물성과 분산성에 미치는 영향
홍양기(Y. K. Hong),정홍식(H. S. Jung),박상준(S. J. Park) 한국자기학회 1996 韓國磁氣學會誌 Vol.6 No.2
It has been known that during magnetic orientation of magnetic Ba-ferrite paint, particle stacking occurs, but also this stacking is found to occur in dry milling process of Ba-ferrite powder in this study. Edge mill was used for dry milling of substituted Ba-ferrite powder. The coercivity of milled Ba-ferrite powder increases linearly with its tap density, and is more dependent on pressure inside a mill than milling time. It is observed by TEM that an increase in the coercivity is attributed to the stacking of particles. A degree of tape's gloss is getting lower with increasing the tap density, which indicates poor dispersibility. The magnetic tape with 1.3 g/㎤ of tap density showed the highest squareness ratio and orientation ratio in the range of 1.1 to 1.7 g/㎤. Excessive dry milling process caused the particles to form clusters, and consequently the dispersibility and orientation became poor.
고밀도 자기기록용 Ba - Ferrite 분말의 자기적 물성과 입자특성에 미치는 Co+²와 Ti+⁴의 효과
홍양기(Y. K. Hong),박상준(S. J. Park),정홍식(H. S. Jung) 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.4
The sites for Fe+³ are partly substituted by Co+² and Ti+⁴ cations to control coercivity of Ba-ferrite particles for use in high density magnetic recording. The substituted Co+² cation has very much different effects on magnetic properties and particle characteristics from that Ti+⁴ cation has. The decrease in the coercivity with the Co+² substitution is attributed to the formation of excessive spinel-block(S-block) in pure Ba-ferrite crystal, while saturation magnetization is increased and the distributions of coercivity and particle size become broad. The substitution with the Ti+⁴ decreases the sauration magnetization, but has less effect on a change in coercivity than the Co+². The Ti+⁴ acts as a nucleation agent in amorphous phase of formulated compound, and consequently particle size and aspect ratio are decreased. Furthermore, the enhancement of substitution of the Co+² for the Fe+³ sites in rhombohedral-block(R-block) by the Ti+⁴ retards the nucleation of spinel phase of Ba-ferrite, which results in uniform magnetic properties of Ba-ferrite particles. It is suggested that the contents of the cations to be substituted for the Fe+³ sites are optimized on the bases of magnetic properties and particle characteristics rather than on the base of electrical charge balance.
자기기록용 치환형 Ba - Ferrite 분말과 Tape의 보자력 차이에 관한 연구
홍양기(Y. K. Hong),정홍식(H. S. Jung),김현준(H. J. Kim) 한국자기학회 1996 韓國磁氣學會誌 Vol.6 No.4
A coercivity of barium ferrite (BaM) tape was found to be higher than the coercivity of BaM powder. This difference is in the range of 50 Oe to 600 Oe, which depends on substituted cations, physical properties of powder, and preparation conditions of the tape. The coercivity difference is attributed to both particle stacking and adsorption of organic solvent on particle surface. Regardless of substituted cations, the coercivity of longitudinally oriented BaFe tape was higher than that of BaM powder by a range of 100 Oe to 120 Oe, which is caused by particle stacking. During the active adsorption process on preparation of magnetic paint, where MEK (methyl ethyl ketone), TOL (toluene) and CHO (cyclohexanone) were used, chemisorption of solvents on the surface of substituted BaFe particle occurred to form polymeric compounds surrounding the particle. An increase in coercivity, caused by the solvent adsorption, was significant for Co-substutited BaM tape. Among these solvents CHO was the most effective one in increasing the coercivity of the Co-Ti substituted BaM tape.
Ba-Ferrite 단결정의 자기적 특성에 관한 뫼스바우어 분광학적 연구
서정철,지성훈,홍양기,Sur, J.C.,Gee, S.H.,Hong, Y.K. 한국자기학회 2007 韓國磁氣學會誌 Vol.17 No.2
Ba-Ferrite single crystals were prepared and characterized by X-ray, SEM and Mossbauer spectroscopy. The single crystal layers was cut in the c-axis and radiated to the surface by ${\gamma}-rays$ for Mossbauer spectroscopy. We found out that the spin states in Fe atoms were parallel to the ${\gamma}-rays$ direction. The temperature dependence of the hyperfine field is almost similar to that of powder samples. The crystal structure is a Magnetoplumbite without any other phases and the lattice parameters are found out with $a_0=5.892{\AA},\;b_0=5.892{\AA},\;c_0=23.198{\AA}$. $M\"{o}ssbauer$ spectrum in single crystal have 5 sets off absorption lines in each Fe site when the ${\gamma}-rays$ have the same radiation direction with the c-axis in the crystal, which mean that the whole crystal bulk formed only one crystal and same spin direction. The hysteresis curve shows the saturation moment and coercive force of 70.71 emu/g and 320 Oe respectively. Ba-ferrite 단결정을 제조하여 자기적 성질을 Mossbauer 분광법으로 연구하였다. 단결정 시료를 c-축 방향으로 얇게 절단하고 그 면에 감마선을 조사한 결과 결정 전체에 걸쳐 Fe 이온의 스핀 방향이 c-축과 일치함을 확인하였다. 온도에 따른 초미세자기장의 감소 추세는 입자상태와 거의 비슷하였으며 결정 내 Fe원자의 이온 상태 역시 일치하였다. 결정구조는 Magnetoplumbite로서 결정상수는 $a_0=5.892{\AA},\;b_0=5.892{\AA},\;c_0=23.198{\AA}$로 정되었으며 그 외의 다른 상은 존재하지 않는 것으로 나타났다. $M\"{o}ssbauer$ spectrum은 결정 내에 존재하는 Fe의 자리에 따라 5의 각각의 다른 subspectrum이 존재하였는데 감마선의 방향이 c-축과 일치하여 모든 자리에서 4개의 공명흡수선 만이 존재하였다. 따라서 결정의 형태는 전체적으로 단일상으로 형성되었음을 확인하였고 여분의 ${\alpha}-Fe_2O_3$ 등은 존재하지 않음을 명확히 하였다. 자기이력곡선을 통하여 실온상태에서 포화자기모멘트는 70.71 emu/g, 보자력이 320 Oe의 값으로 측정되었다.