GANZHORN ET AL. VOL. 7 ’ NO. 7 ’ 6225–6236 ’ 2013 www.acsnano.org 6225 June 26, 2013 C 2013 American Chemical Society Carbon Nanotube Nanoelectromechanical Systems as Magnetometers for Single-Molecule Magnets Marc Ganzhorn, † Svetlana Klyatskaya, ‡ Mario Ruben, ‡,§ and Wolfgang Wernsdorfer †, * † Institut Néel, CNRS & Université Joseph Fourier, BP 166, 25 Avenue des Martyrs, 38042 Grenoble Cedex 9, France, ‡ Institut of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany, and § IPCMS, Université de Strasbourg, 67034 Strasbourg, France A single-molecule magnet (SMM) con- sists of magnetic centers, typically transition metal ions, embedded in a shell of organic ligands. 1,2 The ligands are designed to ensure the bonding of the molecule to surfaces or junctions while preserving and enhancing the ions' mag- netic properties. The magnetic centers will therefore behave as a single “giant” spin due a strong interaction promoted by the ligands. 1 Moreover, one can replace the mag- netic centers and therefore alter the mag- netic properties of the compound without affecting the ligand shell and the interaction with its environment. 1,3 One can also modify the organic ligands by chemical engineering in order to change the SMM's coupling to its environment 1,2 or promote the selective grafting to a certain material, for example, carbon nanotubes or graphene. 4,5 Eventually, chemical engineering allows the synthesis of billions of perfectly identical molecules and would enable the high density integration of molecular spintronic devices. 1,2 Provided with a large spin ground state combined with a strong uniaxial magnetic anisotropy, SMMs exhibit a wide range of quantum mechanical phenonoma such as quantum tunneling of magnetization 6,7 or quantum phase interference. 8 However, probing the quantum mechanical nature of an individual SMM still remains a con- siderable challenge. Various detector designs for individual single-molecule magnets (SMMs) were conse- quently proposed over the past decade. 1 One can use for instance a scanning tunneling microscope to probe an isolated SMM on a conducting surface. 9À12 Alternatively, one can build a three-terminal molecular spin transis- tor where an individual SMM is bridging the gap between two nonmagnetic leads. 13,14 In such a configuration, the electric current is flowing directly through the molecule, leading to a strong coupling between the electrons and the magnetic core. This direct coupling thus enables a readout of the molecule's magnetic properties with the electronic cur- rent but also leads to a strong back-action on the molecule's magnetic core. 1 A less invasive approach consists of cou- pling the SMM to a second nonmagnetic * Address correspondence to wolfgang.wernsdorfer@grenoble.cnrs.fr. Received for review April 30, 2013 and accepted June 26, 2013. Published online 10.1021/nn402968k ABSTRACT Due to outstanding mechanical and electronic proper- ties, carbon nanotube nanoelectromechanical systems (NEMS) were recently proposed as ultrasensitive magnetometers for single-molecule magnets (SMM). In this article, we describe a noninvasive grafting of a SMM on a carbon nanotube NEMS, which conserves both the mechanical properties of the carbon nanotube NEMS and the magnetic properties of the SMM. We will demonstrate that the nonlinearity of a carbon nanotube's mechanical motion can be used to probe the reversal of a molecular spin, associated with a bis(phthalocyaninato)terbium(III) single-molecule magnet, providing an experimental evidence for the detection of a single spin by a mechanical degree of freedom on a molecular level. KEYWORDS: carbon nanotube . NEMS . magnetometer . single-molecule magnets ARTICLE