Origin of slow magnetic relaxation in Kramers ions with non-uniaxial anisotropy

• Published in: Nature communications Vol. 5; no. 1; p. 4300
• Main Authors: Gómez-Coca, Silvia, Urtizberea, Ainhoa, Cremades, Eduard, Alonso, Pablo J., Camón, Agustín, Ruiz, Eliseo, Luis, Fernando
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2014; Nature Publishing Group
• Subjects: 119/118; 639/301/119/997; 639/638/263; Anisotropy; Energy; Humanities and Social Sciences; Molecular structure; multidisciplinary; Science; Science (multidisciplinary); Temperature; Spain
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms5300

Transition metal ions with long-lived spin states represent minimum size magnetic bits. Magnetic memory has often been associated with the combination of high spin and strong uniaxial magnetic anisotropy. Yet, slow magnetic relaxation has also been observed in some Kramers ions with dominant easy-plane magnetic anisotropy, albeit only under an external magnetic field. Here we study the spin dynamics of cobalt(II) ions in a model molecular complex. We show, by means of quantitative first-principles calculations, that the slow relaxation in this and other similar systems is a general consequence of time-reversal symmetry that hinders direct spin–phonon processes regardless of the sign of the magnetic anisotropy. Its magnetic field dependence is a subtle manifestation of electronuclear spin entanglement, which opens relaxation channels that would otherwise be forbidden but, at the same time, masks the relaxation phenomenon at zero field. These results provide a promising strategy to synthesize atom-size magnetic memories. Transition metal ions with long-lived spin states represent the minimum size magnetic bit. Here, the authors study the spin–lattice relaxation of a cobalt(II) complex and demonstrate the role of time-reversal symmetry that hinders direct spin–phonon processes regardless of the sign of the magnetic anisotropy.