A new approach for improving exchange-spring magnets

It is demonstrated here that an already ideal exchange-spring magnet can be further improved by intermixing the interface. This is counter-intuitive to the general expectation that optimal exchange-spring magnet behavior requires an ideal, atomically coherent soft-hard interface. Epitaxial Sm-Co/Fe thin-film exchange-spring bilayers are thermally processed, by annealing or high-temperature deposition, to induce interdiffusion. With increasing processing temperature, the hysteresis loop becomes more single-phase-like, yet the magnetization remains fully reversible. The interface is characterized via synchrotron x-ray scattering and electron microscopy elemental mapping. The magnetization behavior is modeled by assuming a graded interface where the material parameters vary continuously. The simulations produce demagnetization curves similar to experimental observations.