The active control of a molecular spin represents one of the main challenges in molecular spintronics. Up to now spin manipulation has been achieved through the modification of the molecular structure either by chemical doping or by external stimuli. However, the spin of a molecule adsorbed on a surface depends primarily on the interaction between its localized orbitals and the electronic states of the substrate. Here we change the effective spin of a single molecule by modifying the molecule/metal interface in a controlled way using a low-temperature scanning tunneling microscope. A nickelocene molecule reversibly switches from a spin 1 to 1/2 when varying the electrode–electrode distance from tunnel to contact regime. This switching is experimentally evidenced by inelastic and elastic spin-flip mechanisms observed in reproducible conductance measurements and understood using first principle calculations. Our work demonstrates the active control over the spin state of single molecule devices through interface manipulation.

Inelastic electron tunneling spectroscopy (IETS) within the junction of a scanning tunneling microscope (STM) uses current-driven spin-flip excitations for an all-electrical characterization of the spin state of a single object. Usually decoupling layers between the single object, atom or molecule, and the supporting surface are needed to observe these excitations. Here we study the surface magnetism of a sandwich nickelocene molecule (Nc) adsorbed directly on Cu(100) by means of X-ray magnetic circular dichroism (XMCD) and density functional theory (DFT) calculations and show with IETS that it exhibits an exceptionally efficient spin-flip excitation. The molecule preserves its magnetic moment and magnetic anisotropy not only on Cu(100), but also in different metallic environments including the tip apex. By taking advantage of this robusteness, we are able to functionalize the microscope tip with a Nc, which can be employed as a portable source of inelastic excitations as exemplified by a double spin-flip excitation process.

Recent advances in scanning probe techniques rely on the chemical functionalization of the probe-tip termination by a single molecule. The success of this approach opens the tantalizing prospect of introducing spin sensitivity through the functionalization by a magnetic molecule. Here, we use a nickelocene-terminated tip (Nc-tip), which offers the possibility of producing spin excitations on the tip apex of a scanning tunneling microscope (STM). We show that when the Nc-tip is a hundred pm away from point contact with a surface-supported object, magnetic effects may be probed through changes in the spin excitation spectrum of nickelocene. We use this detection scheme to simultaneously determine the exchange field and the spin polarization of the sample with atomic-scale resolution. Our findings demonstrate that the Nc-tip is a powerful probe for investigating surface magnetism with STM, from single magnetic atoms to surfaces.

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The ability to electrically-drive spin excitations in molecules with magnetic anisotropy is key for high-density storage and quantum-information technology. Electrons, however, also tunnel via the vibrational excitations unique to a molecule. The interplay of spin and vibrational excitations offers novel routes to study and, ultimately, electrically manipulate molecular magnetism. Here we use a scanning tunneling microscope to electrically induce spin and vibrational excitations in a single molecule consisting of a nickelocene magnetically coupled to a Ni atom. We evidence a vibron-assisted spin excitation at an energy one order of magnitude higher compared to the usual spin excitations of nickelocene and explain it using first-principles calculations that include electron correlations. Furthermore, we observe that spin excitations can be quenched by modifying the Ni-nickelocene coupling. Our study suggests that nickelocene-based complexes constitute a model playground for exploring the interaction of spin and vibrations in the electron transport through single magnetic molecules.Magnetic molecules are potential candidates for information-storing technology [1], molecular spintronics [2] and quantum computing [3], provided that their axial magnetic anisotropy DS 2 z ensures a magnetic bistability among longlived magnetic states. But molecules also vibrate. In particular, in magnetic molecules the interplay of vibrational modes, or vibrons, with the spin degrees of freedom is known to impact the spin lifetime [4][5][6]. Since vibrational modes can couple to the electric charge, producing vibron-assisted electron excitations in transport [7][8][9], expectations are that similar effects should be also observed with the electronic spin [10,11].Concerning this last point, experimental work has predominantly focused on a well-known spin-related manybody effect, the Kondo effect. The electron-vibron interaction in Kondo molecules was shown to produce satellite Kondo resonances in the differential conductance spectra at the bias of the vibron's excitation energy [12][13][14]. These resonances were ascribed to tunneling electrons that have their spin flipped when elastically scattering off the molecular spin, but with sufficient energy to activate a vibrational mode in the molecule [15]. The question arises whether a similar mechanism is also possible with other spin scattering mechanisms that magnetically excite a molecule such as inelastic scattering involving magnetic anisotropy [16]. These so-called spin excitations show great potential in view of an all-electrical manipulation of the molecular spin [17,18].Here, we use scanning tunneling microscopy (STM) to demonstrate the presence of a combined vibrational-spin excitation in a single nickelocene molecule [Ni(C 5 H 5 ) 2 , see Fig. 1(d); noted Nc hereafter] coupled to a Ni atom. Nickelocene is a spin S = 1 molecule of the metallocene family with magnetic anisotropy, where spin excitations produce a sizable increase of the electronic transport [19]. We show that the o...

A single molecule offers to tailor and control the probing capability of a scanning tunneling microscope when placed on the tip. With the help of first-principles calculations, we show that on-tip spin sensitivity is possible through the Kondo ground state of a spin S = 1/2 cobaltocene molecule. When attached to the tip apex, we observe a reproducible Kondo resonance, which splits apart upon tuning the exchange coupling of cobaltocene to an iron atom on the surface. The spin-split Kondo resonance provides quantitative information on the exchange field and on the spin polarization of the iron atom. We also demonstrate that molecular vibrations cause the emergence of Kondo side peaks, which, unlike the Kondo resonance, are sensitive to cobaltocene adsorption. 1Introduction. The decoration of metal probe-tips by a molecule intentionally picked up from a surface has proven to be a powerful method to improve the measurement capabilities of a scanning tunneling microscope (STM). The degrees of freedom of the molecule introduce tip-surface interactions across the vacuum gap that are usually absent when using a metallic apex. These interactions can endow STM with an enhanced sub-molecular resolution, 1-3 and provide new chemical insight. [4][5][6][7] Detailed information can be gathered about single molecules on a surface and the way they interact among each other, which is of interest to chemistry and biology. 8To probe magnetic effects with a molecular tip it is necessary to have a magnetic molecule at the tip apex. Recently, a tip decorated with a nickelocene molecule 9 [Ni(C 5 H 5 ) 2 ] was used to monitor surface magnetism through the inelastic component of the tunneling current, 10,11 which provides an electrical access to the nickelocene spin states. 12 An exciting alternative could consist in using a magnetic molecule undergoing a Kondo effect, which is quite common for magnetic molecules adsorbed on metal surfaces. 13 This ubiquitous quantum phenomenon occurs when a magnetic impurity -molecule or atom-couples to a non-magnetic host metal. 14 The conduction electrons of the metal spin-screen the impurity to form a singlet below a temperature T K . The screening occurs coherently causing the emergence of

Artificial lattices derived from assembled atoms on a surface using scanning tunneling microscopy present a platform to create matter with tailored electronic, magnetic, and topological properties. However, artificial lattice studies to date have focused exclusively on surfaces with weak spin–orbit coupling. Here, we illustrate the creation and characterization of quantum corrals from iron atoms on the prototypical Rashba surface alloy BiCu 2 , using low-temperature scanning tunneling microscopy and spectroscopy. We observe very complex interference patterns that result from the interplay of the size of the confinement potential, the intricate multiband scattering, and hexagonal warping from the underlying band structure. On the basis of a particle-in-a-box model that accounts for the observed multiband scattering, we qualitatively link the resultant confined wave functions with the contributions of the various scattering channels. On the basis of these results, we studied the coupling of two quantum corrals and the effect of the underlying warping toward the creation of artificial dimer states. This platform may provide a perspective toward the creation of correlated artificial lattices with nontrivial topology.

Combining the complex ordering ability of molecules with their local magnetic properties is a little-explored technique to tailor spin structures on surfaces. However, revealing the molecular geometry can be demanding. Nickelocene (Nc) molecules present a large spin-flip excitation leading to clear changes of conductance at the excitationthreshold bias. Using a superconducting tip, we have the energy resolution to detect small shifts of the Nc spin-flip excitation thresholds, permitting us to reveal the different individual environment of Nc molecules in an ordered layer. This knowledge allows us to reveal the adsorption configuration of a complex molecular structure formed by Nc molecules in different orientations and positions. As a consequence, we infer that Nc layers present a strong non-collinear magnetic moment arrangement.