Epitaxy Induced Highly Ordered Sm₂Co₁₇-SmCo₅ Nanoscale Thin-Film Magnets

Utilizing the molecular beam epitaxy technique, a nanoscale thin-film magnet of c-axis-oriented Sm₂Co₁₇ and SmCo₅ phases is stabilized. While typically in the prototype Sm(Co, Fe, Cu, Zr)_7.5-8 pinning-type magnets, an ordered nanocomposite is formed by complex thermal treatments, here, a one-step approach to induce controlled phase separation in a binary Sm-Co system is shown. A detailed analysis of the extended X-ray absorption fine structure confirmed the coexistence of Sm₂Co₁₇ and SmCo₅ phases with 65% Sm₂Co₁₇ and 35% SmCo₅. The SmCo₅ phase is stabilized directly on an Al₂O₃ substrate up to a thickness of 4 nm followed by a matrix of Sm₂Co₁₇ intermixed with SmCo₅. This structural transition takes place through coherent atomic layers, as revealed by scanning transmission electron microscopy. Highly crystalline growth of well-aligned Sm₂Co₁₇ and SmCo₅ phases with coherent interfaces result in strong exchange interaction, leading to enhanced magnetization and magnetic coupling. The arrangement of Sm₂Co₁₇ and SmCo₅ phases at the nanoscale is reflected in the observed magnetocrystalline anisotropy and coercivity. As next-generation permanent magnets require designing of materials at an atomic level, this work enhances our understanding of self-assembling and functioning of nanophased magnets and contributes to establishing new concepts to engineer the microstructure for beyond state-of-the-art magnets.