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Magnetization reversal in graded magnetic-recording media and its effect on the areal density are investigated by model calculations. By choosing suitable solid-solution materials it is conceptually straightforward, though practically challenging, to achieve arbitrarily low write fields. The writing process involves both the nucleation of reverse domains and their propagation along elongated particles. The performance of the medium is optimized for pinning and nucleation fields of comparable size, and the two fields can be tuned by adjusting the length of the elongated particles (pillars) and the anisotropies of the hard and soft ends. However, the write-field reduction negatively affects the areal density, and there remains a trade-off between write field and bit size.