title: The role of anharmonic phonons in under-barrier spin relaxation of single molecule magnets.
abstract: The use of single molecule magnets in mainstream electronics requires their magnetic moment to be stable over long times. One can achieve such a goal by designing compounds with spin-reversal barriers exceeding room temperature, namely with large uniaxial anisotropies. Such strategy, however, has been defeated by several recent experiments demonstrating under-barrier relaxation at high temperature, a behaviour today unexplained. Here we propose spin-phonon coupling to be responsible for such anomaly. With a combination of electronic structure theory and master equations we show that, in the presence of phonon dissipation, the relevant energy scale for the spin relaxation is given by the lower-lying phonon modes interacting with the local spins. These open a channel for spin reversal at energies lower than that set by the magnetic anisotropy, producing fast under-barrier spin relaxation. Our findings rationalize a significant body of experimental work and suggest a possible strategy for engineering room temperature single molecule magnets.
authors.affiliation: Università degli Studi di Firenze, Dipartimento di Chimica 'Ugo Schiff', Via della Lastruccia 3-13, Sesto Fiorentino 50019, Italy.|School of Physics, AMBER and CRANN, Trinity College, Dublin 2, Ireland.
authors.forename: Alessandro
authors.identifier: 0000-0002-1948-4434
authors.initials: A
authors.lastname: Lunghi
authors.affiliation: Università degli Studi di Firenze, Dipartimento di Chimica 'Ugo Schiff', Via della Lastruccia 3-13, Sesto Fiorentino 50019, Italy.
authors.forename: Federico
authors.identifier: 0000-0003-4752-0495
authors.initials: F
authors.lastname: Totti
authors.affiliation: Università degli Studi di Firenze, Dipartimento di Chimica 'Ugo Schiff', Via della Lastruccia 3-13, Sesto Fiorentino 50019, Italy.
authors.forename: Roberta
authors.identifier: 0000-0003-3783-2700
authors.initials: R
authors.lastname: Sessoli
authors.affiliation: School of Physics, AMBER and CRANN, Trinity College, Dublin 2, Ireland.
authors.forename: Stefano
authors.initials: S
authors.lastname: Sanvito