IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA.
Nano Lett. 2010 Aug 11;10(8):3216-21. doi: 10.1021/nl1022749.
A self-assembled magnetic recording medium was created using colloidal ferrimagnetic building blocks. Monodisperse cobalt ferrite nanoparticles (CoFe(2)O(4)) were synthesized using solution-based methods and then stabilized in solution using the amphiphilic diblock copolymer, poly(acrylic acid)-b-poly(styrene) (PAA-PS). The acid groups of the acrylate block bound the polymer to the nanoparticle surface via multivalent interactions, while the styrene block afforded the magnetic nanoparticle--polymer complex solubility in organic solvents. Moreover, the diblock copolymer improved the colloidal stability of the ferrimagnetic CoFe(2)O(4) nanoparticles by reducing the strong interparticle magnetic interactions, which typically caused the ferrimagnetic nanoparticles to irreversibly aggregate. The nanoparticle--polymer complex was spin-coated onto a silicon substrate to afford self-organized thin film arrays, with the interparticle spacing determined by the molecular weight of the diblock copolymer. The thin film composite was also exposed to an external magnetic field while simultaneously heated above the glass transition temperature of poly(styrene) to allow the nanoparticles to physically rotate to align their easy axes with the direction of the magnetic field. In order to demonstrate that this self-assembled ferrimagnet--polymer composite was suitable as a magnetic recording media, read/write cycles were demonstrated using a contact magnetic tester. This work provides a simple route to synthesizing stabilized ferrimagnetic nanocrystals that are suitable for developing magnetic recording media.
使用胶体铁磁体构建块制备了自组装磁性记录介质。采用基于溶液的方法合成了单分散钴铁氧体纳米粒子（CoFe2O4），然后使用两亲性嵌段共聚物聚（丙烯酸）-b-聚（苯乙烯）（PAA-PS）在溶液中稳定。丙烯酸盐嵌段的酸基团通过多价相互作用将聚合物键合到纳米颗粒表面，而苯乙烯嵌段则使磁性纳米颗粒-聚合物复合物在有机溶剂中具有溶解性。此外，两亲性嵌段共聚物通过降低通常导致铁磁纳米颗粒不可逆聚集的强颗粒间磁性相互作用，提高了铁磁 CoFe2O4 纳米颗粒的胶体稳定性。将纳米粒子-聚合物复合物旋涂到硅基底上，得到自组织的薄膜阵列，颗粒间的间隔由嵌段共聚物的分子量决定。在同时加热到聚苯乙烯玻璃化转变温度以上的情况下，将薄膜复合材料暴露于外磁场中，以允许纳米颗粒物理旋转，使其易轴与磁场方向对齐。为了证明这种自组装铁磁体-聚合物复合材料适合作为磁记录介质，使用接触磁测试仪演示了读写循环。这项工作提供了一种简单的方法来合成稳定的铁磁纳米晶体，适合开发磁记录介质。
