|Budget Amount *help
¥14,900,000 (Direct Cost : ¥14,900,000)
Fiscal Year 2003 : ¥6,900,000 (Direct Cost : ¥6,900,000)
Fiscal Year 2002 : ¥8,000,000 (Direct Cost : ¥8,000,000)
The exchange anisotropy of pseudo-single crystalline Mn-Ir/Co-Fe bilayers with different crystallographic orientations, such as (110), (001), and (111), was investigated. As results, we found that the unidirectional anisotropy constant, J_K, strongly depends on the crystallographic orientation, while the critical thickness of the AF layer, d_<AF>^<cr>, is similarly 〜 3 nm. As a notable result, the J_K of the (110)-epitaxial bilayer with d_<AF> = 4 nm shows extra large value of 0.73 erg/cm^2. The magnetic anisotropy of the Mn-Ir layer determined from the saturation torque amplitude was 8.5×10^5 erg/cm^3 for (110)-, 5.0×10^4 erg/cm^3 for (001)-, and 10^3 〜 10^4 erg/cm^3 for (111)-bilayer, respectively. From the correlation between the exchange anisotropy and the magnetic anisotropy of the Mn-Ir layer, we conclude that the domain wall model is inadequate to explain these experimental results and the single spin model can do it qualitatively, assuming that the interfacial exchange coupling energy differs in the respective crystallographic orientation.
The effect of long-time annealing on the exchange anisotropy of polycrystalline Mn_<75>Ir_<25> d_<AF>/Co_<70>Fe_<30> 4 nm bilayers was also investigated to induce large unidirectional anisotropy constant, J_K, with very thin antiferromagnetic layer. As a notable result, extra large value of J_K = 0.87 erg/cm^2 was obtained in the bilayer with d_<AF> = 5 nm after 200-h-annealing at 250℃, which is larger than the twice of the maximum value of PtMn/Co-Fe system. According to the single spin ensemble model, established by the investigator, the enlargement of J_K by the long-time annealing is explained as a result of the change of the distribution of antiferromagnet spin directions. The magnetic anisotropy energy of Mn-Ir grains was determined as 7×10^3 erg/cm^3 from the activation energy of the enlarging J_K process, experimentally obtained.