• 한국자기학회지
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• 제24권1호
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• pp.1-10
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• 2014

$Co_2Z$-type hexaferrite 시편을 다양한 합성법을 이용하여 제조하였다. 수열합성법을 이용하여 M-type, $Co_2Y$-type, $Co_2Z$-type을 제조하였으며, 제조된 M-type과 $Co_2Y$-type을 출발물질로 하여 고상반응법(ball milling)과 수열합성법(hydrothermal)으로 $Co_2Z$-type을 제조하였다. 제조된 시편의 결정구조와 미세구조 자기적 성질은 XRD, FESEM, VSM, impedance analyzer를 이용하여 조사하였다. M-type과 $Co_2Y$-type은 단일상의 결정구조를 얻을 수 있었다. 여러 합성법 중에 M+Y ball milling, M+Y hydrothermal에서 제조한 시편이 $Co_2Z$-type hexaferrite의 단일상과 대체로 일치하는 것을 알 수 있었으며, $Co_2Z$-type의 모든 시편들은 이론적인 포화 자화값(50 emu/g)과 비슷한 값을 나타내었다. 소결한 시편들의 투자율은 시약을 precusor로 하여 제조한 $Co_2Z$-type의 투자율이 가장 높았으며, 열처리 온도가 증가함에 따라 투자율은 낮아졌다. 다른 합성법에서는 열처리 온도에 따른 변화가 거의 나타나지 않는 것을 확인할 수 있었다.

• Journal of the Korean Physical Society
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• 제73권11호
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• pp.1708-1711
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• 2018

The polycrystalline sample of $Ba_2Co_{1.5}Mg_{0.5}Fe_{11.88}Ga_{0.12}O_{22}$ Y-type hexaferrite, doped with Ga-cation, was prepared by using the solid-state reaction method. The crystalline structure of sample was investigated by x-ray diffractometer (XRD), and the magnetic properties of sample were measured by vibrating sample magnetometer (VSM), and $M{\ddot{o}}ssbauer$ spectrometer. The crystal structure of prepared sample was determined to be rhombohedral with space group R-3m. From the temperature dependence of the magnetization curves under 100 Oe between 4.2 and 740 K, two temperature-dependent magnetic transitions occurred in the $Ba_2Co_{1.5}Mg_{0.5}Fe_{11.88}Ga_{0.12}O_{22}$ sample. $M{\ddot{o}}ssbauer$ spectra of the sample were analyzed at various temperatures ranging from 4.2 to 620 K, and the $Ba_2Co_{1.5}Mg_{0.5}Fe_{11.88}Ga_{0.12}O_{22}$ sample showed abrupt changes in $H_{hf}$ and $E_Q$ at 200 K, indicating the spin transition effect. We have also determined the magnetic transition temperature $T_C$, in addition to the temperature dependent magnetization and ZVC measurements.

• 한국결정성장학회지
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• 제31권5호
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• pp.197-202
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• 2021

Z형 육방정 페라이트인 Ba₃Co₂Fe₂₄O₄₁(Ba₃Z)와 Ba_1.5La_1.5Co₂Fe₂₄O₄₁(Ba_1.5La_1.5Z) 분말을 1차 하소 후 용융염 합성법을 통해 합성하였다. Ba₃Z의 경우, 1000℃에서 하소한 결과 M형 육방정 페라이트와 Y형 육방정 페라이트가 합성되었으며, 이후 1150℃와 1200℃에서 소결했을 때 Z형 육방정 페라이트를 얻을 수 있었다. 하지만 Ba_1.5La_1.5Z의 경우 1000℃에서 하소하였을 때 M형 육방정 페라이트와 CoFe₂O₄(Spinel 상) 그리고 LaFeO₃으로 합성되었으며, Z형 육방정 페라이트는 용융염 합성 과정에서 합성되지 않았다. 또한 입자 형상의 종횡비는 용융염 합성 시 소결온도가 증가함에 따라 감소하는 경향을 보였다. 따라서 높은 종횡비를 갖는 단상의 Ba_1.5La_1.5Z를 합성하기 위해서는 용융염 합성 전 1차 하소 온도가 Spinel 상이 형성되는 온도보다 낮아야 될 것으로 판단된다.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2015년도 자성 및 자성재료 국제학술대회
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• pp.80-80
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• 2015

• 한국자기학회지
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• 제24권2호
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• pp.56-59
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• 2014

$Ba_2CoZnFe_{12}O_{22}$ 시료를 습식분쇄로 이용한 직접 합성법을 사용하였으며, 소결 조건의 변화에 따른 시료 제조후, x-선 회절기(XRD), 진동시료형 자화율측정기(VSM), 회로망 분석기, 그리고 뫼스바우어 분광기 측정을 이용하여 결정학적 및 자기적 특성을 연구하였다. X-선 회절 실험을 통해 Y-type hexaferrite가 주상임을 알 수 있었고, 소결 온도가 증가할수록 밀도가 증가하였다. 상온에서 10 kOe까지의 자화이력곡선 측정 결과, 포화 자화 값는 모든 시료가 약 33 emu/g으로 비슷한 값이 나왔으며, 보자력은 소결 온도가 증가할수록 감소하였다. 회로망 분석기를 통해 100 MHz부터 4 GHz까지 투자율과 유전율을 측정하였다. 그 결과, 소결 온도가 증가할수록 투자율과 tan ${\delta}_{\mu}$는 감소하였다.

• 한국분말재료학회지
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• 제21권4호
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• pp.256-259
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• 2014

A magnetic powder, M-type barium hexaferrite (BaFe12O19), was consolidated with the spark plasma sintering process. Three different holding temperatures, $850^{\circ}C$, $875^{\circ}C$ and $900^{\circ}C$ were applied to the spark plasma sintering process with the same holding times, heating rates and compaction pressure of 30 MPa. The relative density was measured simultaneously with spark plasma sintering and the convergent relative density after cooling was found to be proportional to the holding temperature. The full relative density was obtained at $900^{\circ}C$ and the total sintering time was only 33.3 min, which was much less than the conventional furnace sintering method. The higher holding temperature also led to the higher saturation magnetic moment (${\sigma}_s$) and the higher coercivity ($H_c$) in the vibrating sample magnetometer measurement. The saturation magnetic moment (${\sigma}_s$) and the coercivity ($H_c$) obtained at $900^{\circ}C$ were 56.3 emu/g and 541.5 Oe for each.

• 한국분말재료학회지
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• 제27권2호
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• pp.126-131
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• 2020

The grain growth behavior of M-type Sr hexaferrite (SrM) grains is investigated with the addition of MnCO₃. First, the SrM powder is synthesized by a conventional solid-state reaction. The powder compacts of SrM are sintered at 1250℃ for 2 h with various amounts of MnCO₃ (0, 0.5, 1.0, and 4.0 mol%). There is no secondary solid phase in any of the sintered samples. Relative density increases when MnCO₃ is added to the SrM. Obvious abnormal grain growth does not appear in any of the SrM samples with MnCO₃. The average grain size increases when 0.5 mol% MnCO₃ is added to the SrM. However, as the amount of MnCO₃ increase to over 0.5 mol%, the average grain size decreases. These observations allow us to conclude that the growth of SrM grains is governed by the two-dimensional nucleation grain growth mechanism, and the critical driving force for the growth of a grain decreases as the amount of MnCO₃ increases.

• Journal of Magnetics
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• 제21권3호
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• pp.315-321
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• 2016

M-Zn (M = Sb, V, Nb) substituted M-type strontium hexaferrites were prepared by a ceramic method. The phase composition, morphology and magnetic properties were studied by x-ray diffractometry, scanning electron microscopy and vibrating sample magnetometry. Saturation magnetization increases with a substitution up to 75.0 emu/g (2.5 % higher compared to unsubstituted hexaferrite) and then decreases with a further substitution. A coercive field of substituted hexaferrite powders with highest saturation magnetization is more than 3 kOe. Substituted strontium hexaferrite powders prepared in this work are a rare example of high $M_S$ compositions without doping rare-earth elements and would be a promising candidate for a permanent magnet application.

• Journal of the Korean Physical Society
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• 제73권11호
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• pp.1679-1683
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• 2018

Polycrystalline $BaSrCo_2(Fe_{1-x}Al_x)_{12}O_{22}$ (x = 0.00, 0.01, 0.05, and 0.10) samples were synthesized by polymerizable complex method. Based on the Rietveld refinement, crystal structures of the samples were found to be single-phased and determined to be rhombohedral with space group of R-3m. The hysteresis curves of the samples were measured under 15 kOe at various temperatures ranging from 4.2 and 295 K. It shows that they were not saturated with increasing Al ion contents due to the reduction of magnetic anisotropy. $M_{15kOe}$ was decreased with increasing Al ions contents. We expect that non-magnetic Al ions preferentially occupy the up-spin site of $18h_{VI}$, $3b_{VI}$, and $3a_{VI}$. The $M{\ddot{o}}ssbauer$ spectra of the samples were obtained at 295 K, and analyzed with sixsextets for Fe sites corresponding to the Y-type hexaferrite crystallography sites. The <$E_Q$> shows abrupt changes, and the <$H_{hf}$> shows abrupt decreases around x = 0.05 due to the coexistence of magnetic secondary phases.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2017년도 임시총회 및 하계학술연구발표회
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• pp.124-125
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• 2017