Synthesis and magnetic properties of FePt nanocomposite magnets via self-assembled block copolymer templates

Nanocomposite magnets consisting of hard and soft magnetic phases with controlled structures have attracted much attention for permanent magnetic applications owing to their large energy products. However, construction of structurally controlled nanocomposite magnets with the high magnetic performance that is theoretically predicted remains a challenge. We recently developed a novel route for synthesis of inorganic nanocomposites with three-dimensional, periodically ordered spheres, cylinders, or layers in a matrix using self-assembled block copolymer templates. Metal complexes were selectively introduced into a specific copolymer block of the template, and subsequent removal of the copolymers produced nanocomposites that replicated the template structure. Here, we describe a novel method for fabricating FePt nanocomposite magnets consisting of exchange-coupled hard and soft magnetic phases via self-assembled block copolymer templates. The magnetization curves of nanocomposite samples showed single-phase-like hysteresis loops that confirmed efficient exchange coupling between the hard and soft phases. The measured maximum energy product (BH)max exceeded the theoretical value for non-exchange-coupled isotropic FePt. Our method of compositing an inexpensive and abundant element (iron) to yield nanocomposites with properties superior to those of homogeneous materials demonstrates that it is possible to create novel, highly functional materials in a way that is much more cost-effective than conventional approaches.