Expanded graphite 산화물과 자성 나노입자의 복합화는 화학적 방법을 이용하였으며, Ni과 Co 나노입자를 사용하여 간단한 방 법으로 자기적 특성을 가지는 graphite 산화물을 합성하였다. H 2 SO 4 에 (NH 4 )SO 4 을 첨가한 혼합 용액을 제조하여, natural graphite와 반응시키고, 1차 열처리하여 expanded graphite를 제조하였다. 1050 o C에서 30초간 급속 2차 열처리와 화학적 산화 과 정을 거쳐 expanded graphite oxide로 변화시킨 뒤에 Ni(acac) 2 , Co(acac) 3 과 화학적 반응을 통하여 Expanded graphite 산화물자 성 나노입자 복합체를 제조하였다. 결정 구조 분석을 위하여 x-선 회절 측정을 수행하였으며, Raman 분광 측정으로 graphite 산 화물의 층상 구조를 분석하였다. 미세구조 분석을 위하여 투과전자현미경 측정을 수행하였으며, 진동시료형 자화율측정기를 이용 하여 복합체의 자기적 특성을 연구하였다. 이러한 연구 결과는 graphite 화합물과 자성 물질의 복합화를 위한 기저 기술로 활용 될 수 있을 것이다.

Core-shell magnetic particles with magnetization properties have been extensively studied by various analysis tools [1][2][3][4]. The transmission electron microscope (TEM) and scanning transmission electron microscope (STEM) is a powerful tool to research the crystallographic and chemical properties [5]. Moreover, differential phase contrast (DPC) in STEM is an attractive function for characterization of magnetic or electric properties.We present results using novel DPC technique to give information about magnetic domain contrast and its vector direction in core-shell magnetic particles. This technique uses sensitivity direction detectors to measure quantitatively the deflection of the electron beams when they are influenced by magnetic field [6][7]. Typically it uses a divided annular dark-field detector with four segments. If deflections of electron beam occur at any location in the specimen, it makes its own specific contrast reflecting components at that position. The in-plane field deflects the beam also cause a new contrast by subtracting perpendicular segments of a detector. In addition, we can show the vector direction of magnetic field by simulation with avizo software.The core-shell CoFe2O4@MnFe2O4 magnetic particles with the sizes of ~500nm were prepared by solvo-thermal method. The magnetic properties of these magnetic particles were characterized using STEM (Model TalosF200X) installed DPC detectors. The crystal structures were investigated using SAED pattern in TEM. The chemical compositions of magnetic particles were analyzed by EDS Spectrum, mapping using 4 SDD Super-X Detectors.

The olivine structured LiFe 0.9 Mn 0.1 PO 4 material was prepared by solid state method, and was analyzed by x-ray diffractometer (XRD), superconducting quantum interference devices (SQUID) and Mössbauer spectroscopy. The crystal structure of LiFe 0.9 Mn 0.1 PO 4 was determined to be orthorhombic (space group: Pnma) by Rietveld refinement method. The value of Néel temperature (T N ) for LiFe 0.9 Mn 0.1 PO 4 was determined 50 K. The temperature dependence of the magnetization curves showed magnetic phase transition from paramagnetic to antiferromagnetic at T N by SQUID measurement. Mössbauer spectra of LiFe 0.9 Mn 0.1 PO 4 showed 2 absorption lines at temperatures above T N and showed asymmetric 8 absorption lines at temperatures below T N . These spectra occurred due to the magnetic dipole and electric quardrupole interaction caused by strong crystalline field at asymmetric FeO 6 octahedral sites.