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Gaining control over the grafting geometry is critically important for any application of surface‐supported single‐molecule magnets (SMMs) in data storage, spintronics, and quantum information science. Here, tetrairon(III) SMMs with a propeller‐like structure are functionalized with thioacetyl‐terminated alkyl chains to promote chemisorption on gold surfaces from solution and to evaluate differences in adsorption geometry and magnetic properties as a function of chain length. The prepared monolayers are investigated using X‐ray absorption techniques with linearly and circularly polarized light to extract geometrical and magnetic information, respectively. All derivatives remain intact and form partially oriented monolayers on the gold surface. A ligand‐field analysis of the observed X‐ray natural linear dichroism shows that the threefold molecular axis is invariably biased toward the surface normal, in agreement with ab initio calculations. This preferential orientation is most pronounced in monolayers of the shortest‐chain derivative, which are further studied with an ultralow temperature X‐ray magnetic circular dichroism setup operating down to 350 mK. The isothermal field sweeps with the magnetic field at normal incidence show an open hysteresis loop below 1 K, while measurements at different incidence angles prove the magnetic anisotropy of the monolayers. [ABSTRACT FROM AUTHOR]

Fe8 high-spin molecules exhibit quantum spin tunneling at very low temperatures. Eight Fe3+ ions are sixfold coordinated and magnetically coupled through oxygen bridges. The net magnetization (MS=20 μB per molecule) results from competing antiferromagnetic interactions between the various Fe3+ ions (S=5/2). Because of the structural anisotropy of these molecules, the magnetization curve presents a hysteresis loop with staircases below 2 K. The staircases of the hysteresis loop are due to the quantum spin tunneling, which is temperature dependent for 400 mK3He-4He dilution refrigerator. This device, that takes advantage of the thermodynamic particularities of the 3He-4He mix, let us obtain x-ray magnetic circular dichroism (XMCD) spectra at 300 mK for this molecule. It has been possible to register an XMCD remnant signal, without magnetic field applied, at the iron L2,3 edges. XMCD coupled with ligand field multiplet calculations has allowed to determine the spin and orbit contributions to the magnetization of the Fe3+ ions. [ABSTRACT FROM AUTHOR]