Fabrication of magnetic nanoparticle-array recording media and their evaluation with probe heads

本研究的目的是建立Fe-Pt纳米颗粒阵列磁记录介质的制造技术，并评估其实现超过1太比特/平方英寸的面记录密度的潜力。主要结果如下：1）研究了Fe-Pt纳米颗粒粉末样品的化学有序性与磁各向异性的关系，发现用穆斯堡尔谱测量的有序合金相的体积比Q是一个评价化学有序性的有用参数。而Q是短程有序的参数，从X射线衍射法获得的S是长程有序的参数。用90 kOe的最大磁场评价磁各向异性。部分有序Fe-Pt纳米颗粒的磁各向异性场H_k分布比几乎完全有序的Fe-Pt纳米颗粒的磁各向异性场H_k分布宽得多，并且包含了高体积比的低H_k组分 ...更多信息 采用多元醇还原法，在微波辐射下，不经任何后处理，成功地制备了铁盐和铂盐纳米粒子。在250℃微波辐射下合成的Fe-Pt纳米粒子的有序合金相体积比为60%，磁各向异性场大于80 kOe。3）将饱和脂肪酸（C_nH_<2n>O_2）分子加入到Fe-Pt纳米粒子悬浮液中，在纯水表面形成纳米粒子单层膜，而不发生凝聚。由于Fe-Pt纳米粒子表面具有疏水性，与水表面的界面能较高。脂肪酸分子可能作为Fe-Pt纳米粒子单层膜与水表面之间的缓冲层降低了界面能。n ≥ 14的脂肪酸分子对Fe-Pt纳米粒子组装膜的形成是有效的，从形成规则纳米粒子阵列的角度来看，n = 14的脂肪酸分子是最好的。4）在Fe-Pt纳米粒子组装膜上溅射沉积碳涂层，成功地防止了组装膜的粒子间烧结。Fe-Pt纳米粒子的直径为4-5 nm，保持物理隔离和化学有序后，最佳的热处理。然而，需要更高的温度和更长的热处理时间来实现适当的化学排序，以适应未来记录系统的高密度记录介质的规格。在最佳条件下退火的具有碳涂层的Fe-Pt纳米颗粒组装膜显示出颗粒尺寸为4-5 nm，磁各向异性常数为4.8 × 10^7 erg/cm^3。少

The purpose of the present study is to establish fabrication techniques of Fe-Pt nanoparticle-array magnetic recording media and to evaluate their potential to achieve areal recording density over 1 tera-bit per square inch. The results are shown in the followings.1) We studied the relationship between chemical ordering and magnetic anisotropy for powder samples of Fe-Pt nanoparticles, and found that a volume ratio Q of ordered alloy phase evaluated with Mossbauer spectroscopy was a useful parameter to evaluate the chemical ordering. Whereas Q is a parameter for short-range ordering, S obtained from X-ray diffractometry is a parameter for long-range ordering. Magnetic anisotropy was evaluated with the maximum magnetic field of 90 kOe. Distribution of magnetic anisotropy-field H_k for partially ordered Fe-Pt nanoparticles was much broader than that for almost fully ordered Fe-Pt nanoparticles, and the low H_k components were included with a high volume ratio.2) Partially ordered Fe-Pt n … More anoparticles were successfully obtained with polyol reduction method of Fe and Pt salts by using microwave irradiation without any post-synthesis heat-treatment. The Fe-Pt nanoparticles synthesized at 250℃ with microwave irradiation exhibited volume ratio for ordered alloy phase of 60% and magnetic anisotropy field over 80 kOe.3) Mixing saturated fatty acid (C_nH_<2n> O_2) molecules to an Fe-Pt nanoparticle suspension assisted the formation of a nanoparticle monolayer on pure water surface without coagulation. Because the surface of the Fe-Pt nanoparticles is hydrophobic, interface energy with water surface is high. The fatty acid molecules probably reduced the interface energy as a buffer layer between the Fe-Pt nanoparticle-monolayer and water surface. Fatty acid molecules with n 【greater than or equal】 14 were effective for the formation, and the best one in view of the formation of regular nanoparticle-array was the molecule with n = 14.4) Carbon overcoats deposited with sputtering on Fe-Pt nanoparticle assembly-films successfully prevented the assembly-films from inter-particle sintering. Fe-Pt nanoparticles of 4-5 nm in diameter were kept isolated physically and were chemically ordered after an optimum heat-treatment. However, higher temperature and longer time for the heat treatment were required to achieve proper chemical ordering to fit a specification of high-density recording media for future recording system. Fe-Pt nanoparticle assembly-films with a carbon overcoat annealed under the optimum conditions exhibited that the particle size was 4-5 nm and magnetic anisotropy constant was 4.8x10^7 erg/cm^3. Less