Remanence and coercivity are the basic characteristics of permanent magnets. They are also tightly correlated with the existence of long relaxation times of magnetization in a number of molecular complexes, called accordingly single-molecule magnets (SMMs). Up to now, hysteresis loops with large coercive fields have only been observed in polynuclear metal complexes and metal-radical SMMs. On the contrary, mononuclear complexes, called single-ion magnets (SIM), have shown hysteresis loops of butterfly/phonon bottleneck type, with negligible coercivity, and therefore with much shorter relaxation times of magnetization. A mononuclear ErIII complex is presented with hysteresis loops having large coercive fields, achieving 7000â Oe at T=1.8â K and field variation as slow as 1â h for the entire cycle. The coercivity persists up to about 5â K, while the hysteresis loops persist to 12â K. Our finding shows that SIMs can be as efficient as polynuclear SMMs, thus opening new perspectives for their applications.