Improving exchange-spring nanocomposite permanent magnets

We demonstrate a counterintuitive approach for improving exchange-spring magnets. Contrary to the general belief that the exchange–spring interface must be ideal and atomically coherent, we thermally process, by annealing or high-temperature deposition, epitaxial Sm–Co/Fe thin-film bilayers to induce interfacial mixing. Synchrotron x-ray scattering and electron microscopy elemental mapping confirm the formation of a graded interface. The thermal processing enhances the nucleation field and the energy product. The hysteresis loop becomes more single-phase-like yet the magnetization remains fully reversible. Model simulations produce demagnetization behaviors similar to experimental observations. © 2004 American Institute of Physics. [DOI: 10.1063/1.1828225]