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Magnetic Bistability of Isolated Giant‐Spin Centers in a Diamagnetic Crystalline Matrix
Author(s) -
Vergnani Luca,
Barra AnneLaure,
Neugebauer Petr,
RodriguezDouton Maria Jesus,
Sessoli Roberta,
Sorace Lorenzo,
Wernsdorfer Wolfgang,
Cornia Andrea
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201103251
Subject(s) - diamagnetism , condensed matter physics , magnetization , chemistry , electron paramagnetic resonance , nanomagnet , magnetic anisotropy , magnetic field , nuclear magnetic resonance , physics , quantum mechanics
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.