GIANT EXCHANGE ANISOTROPY OF FERROMAGNETIC/ANTIFERROMAGNETIC BILAYERS INDUCED BY THE CONTROLE OF THEIR MICROSTRUCTURE AND INTERFACE

研究了（110）、（001）、（111）等不同取向的Mn-Ir/Co-Fe伪单晶双分子层的交换各向异性。结果表明，单向各向异性常数J_K强烈依赖于晶体取向，而AF层的临界厚度d_<AF>^<cr>同样为~ 3nm。结果表明，当d_< af> = 4 nm时，(110)-外延双分子层的J_K值达到了0.73 erg/cm^2。饱和转矩振幅测定的Mn-Ir双分子层磁各向异性分别为(110)- 8.5×10^5 erg/cm^3, (001)- 5.0×10^4 erg/cm^3, (111)- 10^3 ~ 10^4 erg/cm^3。从交换各向异性与Mn-Ir层磁各向异性之间的关系来看，假设界面交换耦合能在各自的晶体取向上不同，畴壁模型不足以解释这些实验结果，单自旋模型可以定性地解释这些实验结果。研究了长时间退火对多晶Mn_<75>Ir_<25> d_<AF>/Co_<70>Fe_<30> 4 nm双分子层交换各向异性的影响，得到了具有极薄反铁磁层的大的单向各向异性常数J_K。结果表明，d_< af> = 5 nm双分子层经250℃200-h退火后，J_K = 0.87 erg/cm^2，大于PtMn/Co-Fe体系最大值的2倍。根据研究者建立的单自旋系综模型，长时间退火导致的J_K的增大可以解释为反铁磁体自旋方向分布的改变。根据实验得到的放大J_K过程的活化能，确定Mn-Ir晶粒的磁各向异性能为7×10^3 erg/cm^3。

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.