Magnetic memory of a single-molecule quantum magnet wired to a gold surface

Molecular magnets are promising for their use as high-density memory devices. However, maintaining the molecules’ magnetic state when bonded to a substrate has been impossible. The discovery, in sophisticated experiments, that single magnetic molecules can indeed show magnetic hysteresis when wired to a gold surface opens the door to individually address magnetic molecules. In the field of molecular spintronics1, the use of magnetic molecules for information technology is a main target and the observation of magnetic hysteresis on individual molecules organized on surfaces is a necessary step to develop molecular memory arrays. Although simple paramagnetic molecules can show surface-induced magnetic ordering and hysteresis when deposited on ferromagnetic surfaces2, information storage at the molecular level requires molecules exhibiting an intrinsic remnant magnetization, like the so-called single-molecule magnets3 (SMMs). These have been intensively investigated for their rich quantum behaviour4 but no magnetic hysteresis has been so far reported for monolayers of SMMs on various non-magnetic substrates, most probably owing to the chemical instability of clusters on surfaces5. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism synchrotron-based techniques, pushed to the limits in sensitivity and operated at sub-kelvin temperatures, we have now found that robust, tailor-made Fe4 complexes retain magnetic hysteresis at gold surfaces. Our results demonstrate that isolated SMMs can be used for storing information. The road is now open to address individual molecules wired to a conducting surface6,7 in their blocked magnetization state, thereby enabling investigation of the elementary interactions between electron transport and magnetism degrees of freedom at the molecular scale8,9.