We have measured quantum transport through an individual Fe(4) single-molecule magnet embedded in a three-terminal device geometry. The characteristic zero-field splittings of adjacent charge states and their magnetic field evolution are observed in inelastic tunneling spectroscopy. We demonstrate that the molecule retains its magnetic properties and, moreover, that the magnetic anisotropy is significantly enhanced by reversible electron addition/subtraction controlled with the gate voltage. Single-molecule magnetism can thus be electrically controlled.

We study three-terminal charge transport through individual Fe 4 single-molecule magnets. Magnetic anisotropy of the single molecule is directly observed by introducing a spectroscopic technique based on measuring the position of the degeneracy point as a function of gate voltage and applied magnetic field. A nonlinear field-dependence is observed which changes by rotating the sample and is, thus, a direct proof of magnetic anisotropy. The sensitivity of this method allows us to observe small changes in the orientation and magnitude of the anisotropy in different charge states. We find that the easy axes in adjacent states are (almost) collinear. DOI: 10.1103/PhysRevLett.109.147203 PACS numbers: 75.50.Xx, 73.23.Hk, 73.63.Àb, 75.30.Gw Molecular spintronics proposes a new route to information storage and processing based on the electrical addressing of magnetic states in individual molecules [1,2]. Magnetic molecules usually have long spin coherence and spin relaxation times [3] which are of crucial importance for information processing. In addition, versatility in synthesis allows us to produce a wide variety of molecular systems with almost tailor-made properties. Singlemolecule magnets (SMMs) [4,5] are of particular interest for their magnetic anisotropy, which lifts spin degeneracy even at zero field and generates an energy barrier U that opposes spin reversal. Under favorable conditions, the molecular spin and magnetic anisotropy can be relatively large producing a sizeable hysteresis; each molecule behaves, therefore, as a nanomagnet. Addressing the magnetic states of single molecules remains, however, a challenging task, in spite of recent efforts [6][7][8].Early attempts to measure the properties of individual SMMs focused on Mn 12 clusters [9,10] and were followed by experiments on Fe 4 complexes [11,12]. Alternatively, TbPc 2 molecules were deposited on carbon nanotubes [13] and graphene layers [14] attached to metallic electrodes. In these systems, the conductance through the carbon structure serves as a probe of molecular magnetic properties. Spin flips were measured this way. However, no direct evidence of the magnetic anisotropy in the current flowing through a magnetic molecule has been reported yet. For this same reason, little is known [11,12] about the changes of magnetic anisotropy when the molecule is electrically charged.In this Letter, we report on single-electron transport through a single Fe 4 molecule in a three-terminal geometry sketched in Fig. 1(a). We measured the anisotropy of an individual SMM in different charge states by measuring the position of the charge degeneracy point as a function of magnetic field. This gate-voltage spectroscopy should be contrasted to conventional transport spectroscopy as the gate voltage is the only control parameter. Moreover, the method does not rely on the detection of single-electron transport (SET) or cotunneling excitations as in Ref. [11] and it is, therefore, less sensitive to the coupling À between molecule and electrodes; its applicability ...

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Inspired by cotunneling spectroscopy of spin-states in a single OPE5-based molecule, we investigate the prospects for electric control of magnetism in purely organic molecules contacted in a three-terminal geometry. Using the gate electrode, the molecule is reversibly switched between three different redox states, with magnetic spectra revealing both ferromagnetic and antiferromagnetic exchange couplings on the molecule. These observations are shown to be captured by an effective low-energy Heisenberg model, which we substantiate microscopically by a simple valence bond description of the molecule. These preliminary findings suggest an interesting route towards functionalized all-organic molecular magnetism.

Purpose: Extremity cone‐beam CT (CBCT) with an amorphous silicon (aSi) flat‐panel detector (FPD) provides low‐dose volumetric imaging with high spatial resolution. We investigate the performance of the newer complementary metal‐oxide semiconductor (CMOS) detectors to enhance resolution of extremities CBCT to ∼0.1 mm, enabling morphological analysis of trabecular bone. Quantitative in‐vivo imaging of bone microarchitecture could present an important advance for osteoporosis and osteoarthritis diagnosis and therapy assessment. Methods: Cascaded systems models of CMOS‐ and FPD‐based extremities CBCT were implemented. Performance was compared for a range of pixel sizes (0.05–0.4 mm), focal spot sizes (0.3–0.6 FS), and x‐ray techniques (0.05–0.8 mAs/projection) using detectability of high‐, low‐, and all‐frequency tasks for a nonprewhitening observer. Test‐bench implementation of CMOS‐based extremity CBCT involved a Teledyne DALSA Xineos3030HR detector with 0.099 mm pixels and a compact rotating anode x‐ray source with 0.3 FS (IMD RTM37). Metrics of bone morphology obtained using CMOS‐based CBCT were compared in cadaveric specimens to FPD‐based system using a Varian PaxScan4030 (0.194 mm pixels). Results: Finer pixel size and reduced electronic noise for CMOS (136 e compared to 2000 e for FPD) resulted in ∼1.9× increase in detectability for high‐frequency tasks and ∼1.1× increase for all‐frequency tasks. Incorporation of the new x‐ray source with reduced focal spot size (0.3 FS vs. 0.5 FS used on current extremities CBCT) improved detectability for CMOS‐based CBCT by ∼1.7× for high‐frequency tasks. Compared to FPD CBCT, the CMOS detector yielded improved agreement with micro‐CT in measurements of trabecular thickness (∼1.7× reduction in relative error), bone volume (∼1.5× reduction), and trabecular spacing (∼3.5× reduction). Conclusion: Imaging performance modelling and experimentation indicate substantial improvements for high‐frequency imaging tasks through adoption of the CMOS detector and small FS x‐ray source, motivating the use of these components in a new system for quantitative in‐vivo imaging of trabecular bone. Financial Support: US NIH grant R01EB018896. Qian Cao is a Howard Hughes Medical Institute International Student Research Fellow. Disclosures: W Zbijewski, J Siewerdsen and A Sisniega receive research funding from Carestream Health.