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마이크로파 여기 프라즈마법으로 제조한 강자성 터널링 접합의 국소전도특성
윤대식(Tae Sick Yoon),김철기(Cheol Gi Kim),김종오(Chong-Oh Kim),Masakiyo Tsunoda(Masakiyo Tsunoda),Migaku Takahashi(Migaku Takahashi),Ying Li(Ying Li) 한국자기학회 2003 韓國磁氣學會誌 Vol.13 No.2
Ferromagnetic tunnel junctions were fabricated by dc magnetron sputtering and plasma oxidation process. The local transport properties of the ferromagnetic tunnel junctions were studied using contact-mode Atomic Force Microscopy (AFM) and the local current-voltage analysis. Tunnel junctions with the structure of sub./Ta/Cu/Ta/NiFe/Cu/Mn_(75)Ir_(25)/Co_(70)Fe_(30)/Al-oxide were prepared on thermally oxidized Si wafers. Al-oxide layers were formed with microwave excited plasma using radial line slot antenna (RLSA) for 5 and 7 sec. Kr gas was used as the inert gas mixed with O₂ gas for the plasma oxidization. No correlation between topography and current image was observed while they were measured simultaneously. The local current distribution was well identified with the distribution of local barrier height. Assuming the gaussian distribution of the local barrier height, the ferromagnetic tunnel junction with longer oxidation time was well fitted with the experimental results. As contrast, in the case of the shorter time oxidation junction, the current mainly flow through the low barrier height area for its insufficient oxygen. Such leakage current might result in the decrease of tunnel magnetoresistance (TMR) ratio.
Exchange Anisotropy of Polycrystalline Ferromagnetic / Antiferromagnetic Bilayers
Masakiyo Tsunoda,Migaku Takahashi 한국자기학회 2002 Journal of Magnetics Vol.7 No.3
The role of magnetic anisotropy of the antiferromagnetic layer on the magnetization process of exchange coupled polycrystalline ferromagnetic/antiferromagnetic bilayers is discussed. In order to elucidate the magnetic torque response of Ni-Fe/Mn-Ir bilayers, the single spin ensemble model is newly introduced, taking into account the two-dimensionally random distribution of the magnetic anisotropy axes of the antiferromagnetic grains. The mechanism of the reversible inducement of the exchange anisotropy along desirable directions by field cooling procedure is successfully explained with the new model. Unidirectional anisotropy constant, J_K, of polycrystalline Ni-Fe/Mn-Ir and Co-Fe/Mn-Ir bilayers is investigated as functions of the chemical composition of both the ferromagnetic layer and the antiferromagnetic layer. The effects of microstructure and surface modification of the antiferromagnetic layer on J_K are also discussed. As a notable result, an extra large value of J_K, which exceeds 0.5 erg/㎠, is obtained for Co_(70)Fe_(30)/Mn_(75)Ir_(25) bilayer with the ultra-thin (50 Å~100 Å) Mn-Ir layer. The exchange anisotropy of Co_(70)Fe_(30) 40Å/Mn_(75)Ir_(25) 100 Å bilayer is stable for thermal annealing up to 400℃, which is sufficiently high for the application of spin valve magnetoresistive devices.