A single-molecule magnet (SMM) is a metal-organic compound that has superparamagnetic behavior below a certain blocking temperature at the molecular scale. In this temperature range, a SMM exhibits magnetic hysteresis of purely molecular origin. In contrast to conventional bulk magnets and molecule-based magnets, collective long-range magnetic ordering of magnetic moments is not necessary.

Although the term "single-molecule magnet" was first employed in 1996, the first single-molecule magnet, [Mn₁₂O₁₂(OAc)₁₆(H₂O)₄] (nicknamed "Mn₁₂") was reported in 1991. This manganese oxide compound features a central Mn(IV)₄O₄ cube surrounded by a ring of 8 Mn(III) units connected through bridging oxo ligands, and displays slow magnetic relaxation behavior up to temperatures of ca. 4 K.

Efforts in this field primarily focus on raising the operating temperatures of single-molecule magnets to liquid nitrogen temperature or room temperature in order to enable applications in magnetic memory. Along with raising the blocking temperature, efforts are being made to develop SMMs with high energy barriers to prevent fast spin reorientation. Recent acceleration in this field of research has resulted in significant enhancements of single-molecule magnet operating temperatures to above 70 K.