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

研究了(110)、(001)和(111)晶面不同取向的伪单晶Mn-Ir/Co-Fe双层膜的交换各向异性。结果发现，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_&lt；aF&gt；^&lt；cr&gt；类似地约为3 nm。由饱和扭矩幅值测得的(110)-外延双层膜的磁各向异性分别为8.5×105erg/cm^3、5.0×104erg/cm^3和10^3~10.4erg/cm^3。根据Mn-Ir层的交换各向异性与磁各向异性之间的关系，我们得出结论：假设界面交换耦合能在不同的晶体取向上不同，磁畴壁模型不能很好地解释这些实验结果，单自旋模型可以定性地解释这些实验结果。4 nm双层膜具有很薄的反铁磁层，可以诱导出较大的单向各向异性常数J_K。值得注意的是，对于d&lt；Af&gt；=5 nm的双层薄膜，在250℃下经200h退火后，J_k=0.87erg/cm~2，比PtMn/Co-Fe系统的最大值大了一倍。根据作者建立的单自旋系综模型，解释了长时间退火使J_K增大的原因是反铁磁体自旋方向分布的变化。由实验测得的放大J_K过程的激活能，测得Mn-Ir颗粒的磁各向异性能为7×103erg/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.