Magnetic Bistability of Isolated Giant-Spin Centers in a Diamagnetic Crystalline Matrix
Dipartimento di Chimica & UdR INSTM, Università di Modena e Reggio Emilia via G. Campi 183, 41100 Modena, Italy.Chemistry - A European Journal (Impact Factor: 5.73). 03/2012; 18(11):3390-8. DOI: 10.1002/chem.201103251
Polynuclear single-molecule magnets (SMMs) were diluted in a diamagnetic crystal lattice to afford arrays of independent and iso-oriented magnetic units. Crystalline solid solutions of an Fe(4) SMM and its Ga(4) analogue were prepared with no metal scrambling for Fe(4) molar fractions x down to 0.01. According to high-frequency EPR and magnetic measurements, the guest SMM species have the same total spin (S=5), anisotropy, and high-temperature spin dynamics found in the pure Fe(4) phase. However, suppression of intermolecular magnetic interactions affects magnetic relaxation at low temperature (40 mK), where quantum tunneling (QT) of the magnetization dominates. When a magnetic field is applied along the easy magnetic axis, both pure and diluted (x=0.01) phases display pronounced steps at evenly spaced field values in their hysteresis loops due to resonant QT. The pure Fe(4) phase exhibits additional steps which are firmly ascribed to two-molecule QT transitions. Studies on the field-dependent relaxation rate showed that the zero-field resonance sharpens by a factor of five and shifts from about 8 mT to exactly zero field on dilution, in agreement with the calculated variation of dipolar interactions. The tunneling efficiency also changes significantly as a function of Fe(4) concentration: the zero-field resonance is significantly enhanced on dilution, while tunneling at ±0.45 T becomes less efficient. These changes were rationalized on the basis of a dipolar shuffling mechanism and transverse dipolar fields, whose effect was analyzed by using a multispin model. Our findings directly prove the impact of intermolecular magnetic couplings on SMM behavior and disclose the magnetic response of truly isolated giant spins in a diamagnetic crystalline environment.
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ABSTRACT: We present measurements of the magnetic properties of thin film TbPc(2) single-molecule magnets evaporated on a gold substrate and compare them to those in bulk. Zero-field muon spin relaxation measurements were used to determine the molecular spin fluctuation rate of TbPc(2) as a function of temperature. At low temperature, we find that the fluctuations in films are much faster than in bulk and depend strongly on the distance between the molecules and the Au substrate. We measure a molecular spin correlation time that varies between 1.4 μs near the substrate and 6.6 μs far away from it. We attribute this behavior to differences in the packing of the magnetic cores, which change gradually on the scale of ∼10-20 nm away from the TbPc(2)/Au interface.ACS Nano 08/2012; 6(9):8390-6. DOI:10.1021/nn3031673 · 12.88 Impact Factor
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ABSTRACT: Terbium(III) bis-phthalocyaninato neutral complex, a robust and evaporable Single Molecule Magnet (SMM) with a record height of the anisotropy barrier, has recently attracted a great interest as an active unit in single molecule electronics, but at the same time its magnetic hysteresis has been found to be strongly affected when the environment is different from the crystalline phase. Here we present a systematic investigation of the magnetization dynamics in different environments, obtained by magnetic dilution, thermal treatment and sublimation of the molecules, to shed some light on the origin of the evanescence of the hysteretic behavior of this unique SMM.Journal of Materials Chemistry 04/2013; 1(16):2935-242. DOI:10.1039/c3tc00925d · 7.44 Impact Factor
Chapter: Single-Molecule Magnets on Surfaces[Show abstract] [Hide abstract]
ABSTRACT: Encoding and manipulating information through the spin degrees of freedom of individual magnetic molecules or atoms is one of the central challenges in the continuing trend towards molecular/atomic scale electronics. With their large magnetic moment and long spin relaxation time, single-molecule magnets (SMMs) are of special importance in this emerging field. Their electrical addressing at the molecular level appears now well within reach using STM methods, which require to organize SMMs on a conducting surface. In this chapter, we present a critical overview of the latest achievements in the deposition of SMMs as monolayers or submonolayers on native or prefunctionalized surfaces. Special emphasis is placed on the selection and design of molecular structures that withstand solution or vapour-phase processing and that maintain their magnetic functionality on a surface. Chemical strategies to control the strength of molecule–substrate interaction and the molecular orientation on the surface are also illustrated. Rewardingly, these efforts have shown that the distinctive properties of SMMs, i.e. slow spin relaxation and quantum tunnelling of the magnetic moment, persist in metal-wired molecules.07/2014: pages 293-330;
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