Nanocrystalline materials of Ni and Ni-Cu alloy have been synthesized by the pulsed wire evaporation (PWE) method and these abnormal magnetic properties in the magnetic ordered state have been characterized using both VSM and SQUID in the range of high and low magnetic fields. Ni and Ni-Cu particles with an average size of 20 to 80 nm were found to influence magnetic hysterisis behavior and the results of powder neutron diffraction patterns and saturation magnetization curves are shown to indicate the absence of the NiO phase. The shifted hysterisis loop and irreversibility of the magnetization curve in the high field region were observed in the magnetic-ordered state of both Ni and Ni-Cu. The virgin magnetization curve for Ni slightly spillover on the limited hysterisis loop (20kOe). This irreversibility in the high field of 50 kOe can be explained by non-col-linear behavior and the existence of the metastable states of the magnetization at the surface layer (or core) of the particle in the applied magnetic field. Immiscible alloy of Cu-Ni was also found to show irreversibility having two different magnetic phases.

(x=0.69~0.74) powders synthesized by the thermal decomposition of organic acid salts. The obtained powders were uniform in composition and ultra-fine particle with about 400 nm. The amount of spinel phase of these powders was about 50% in X-ray diffraction patterns. The calcination of powder was carried out at for 2 hours in air. After the powders were calcined. the mean size of powder was about 500 nm and the amount of spinel phase was increased over about 65%. The maximum amount of spinel phase was about 75% in the specimen of X=0.72. The magnetic properties of calcined powders were the best among the different among the different compositions

현재 기계적 합금화법에서는 주로 합금을 구성하는 성분원소 분말을 불활성분위기에서 볼밀처리 함으로써 함금화를 시키거나 모합금에 산화물을 분산시켜 복합화시키는 공정을 통하여 각종 화합물, 비정질상 및 과포화고용체등의 준안정상의 합성 뿐만이 아니라 초미세조직의 생성에 관한 폭 넓은 분야의 연구가 행하여지고 있다. 한편 MA에서는 볼멀처리중 기계적 에너지의 투여에 의하여 실제 반응온도보다 낮은 온도에서 발생하는 특이한 화학반응 즉 Mechanochemical

Conventional Fe-Co alloys are important soft magnetic materials that have been widely used in industry. Compared to its polycrystalline counterpart, the nanostructured materials have showed superior magnetic properties, such as higher permeability and lower coercivity due to the single domain configuration. However, magnetic properties of nanostructured materials are affected in complicated manner by their microstructure such as grain size, internal strain and crystal structure. Thus, studies on synthesis of nanostructured materials with controlled microstructure are necessary for a significant improvement in magnetic properties. In the present work, starting with two powder mixtures of Fe and Co produced by mechanical alloying (MA) and hydrogen reduction process (HRP), differences in the preparation process and in the resulting microstructural characteristics will be described for the nano-sized Fe-Co alloy particles. Moreover, we discuss the effect of the microstructure such as crystal structure and grain size of Fe-Co alloys on the magnetic properties.

Nano Cu powders, synthesized by Pulsed Wire Evaporation (PWE) method, have been compacted by Magnetic Pulsed Cojpaction(MPC) method. The microstructure and mechanical properties were analyzed. The optimal condition for proper mechanical properties with nanostructure was found. Both pure nano Cu powders and passivated nano Cu powders were compacted, and the effect of passivated layer on the mechanical properties was investigated. The compacts by MPC, which had ultra-fine and uniform nanostructure, showed higher density of 95% of theoretical density than that of static compaction. The pur and passivated Cu compacted at exhibited maximum hardnesses of 248 and 260 Hv, respectively. The wear resistance of those compacts corresponded to the hardness.

비정질 Tb45.7 Fe54.3-x /Cox 및 Tb50.2 /Fe 49.8-x/Cox (0≤x≤9.6) 합금박막의 자기적 특성 및 자기변형특성에 대하여 체계적으로 조사하였다. 박막제조는 Fe 타게트에 Tb, Co 소편으로 구성된 복합타겟 방식의 rf 마그네트론 스퍼터링법에 의해 제조하였다. XRD 조사에의 한 박막의 미세구조는 잘 발달된 비정질 구조를 나타내었다. Tb45.7 Fe54.3-x Cox (x=2~4)에서 우수한 고유자기변형특성 및 저자기장자기변형특성을 얻었다. 즉, 100 Oe의 저자장에서 130ppm의 자기변형을 나타내었으며 고유자기변형 (인가 자기장, 5 kOe)은 330ppm에서 400ppm으로 증가하였다.

Sr 페라이트 자석의 자기적 특성을 향상시키기 위하여 화학량론적 조건인 SrFe 12O19 [SrM]에서 11.7CoSrFe0.3 O19[Co0.3 -SrM]/ 및 Sr0.7 La0.3F e11.7 Co0.3 O19 /[(La-Co)0.3-SrM] 조성으로 혼합후 공기중 하소를 실시하여 하소분의 특성을 조사하였고, 소결조제와 함께 미분쇄한 후 공기 중에서 소결하여 페라이트 자석을 제조한 후 자기특성 변화를 조사하였다. 화학량론적인 조성에서 (La-Co)0.3-SrM 조성으로 원소치환을 실시한 하소분말을 사용하여 제조한 페라이트 자석의 소결특성은 포화자화 (Ms ) 71.08 emu/g, 보자력 (iHC ) 4.38 kOe 및 잔류자속밀도 (Br ) 4.18 kG, 보자력 (iHC ) 4.35 kOe, 최대에너지적(BHmax ) 4.3 MGOe으로 화학량론적인 조건에 비해 B Hmax가 10% 이상 더 큰 자기특성값을 나타내었다.나타내었다.다.