The properties of two molecular-based magnetic helices, composed of 3d metal Co and Mn ions bridged by nitronyl nitroxide radicals, are investigated by density-functional calculations. Their peculiar and distinctive magnetic behavior is here elucidated by a thorough description of their magnetic, electronic, and anisotropy properties. Metal ions are antiferromagnetically coupled with the radicals, leading to a ferrimagnetically ordered ground state. A strong metal-radical exchange coupling is found, about 44 and 48 meV for Co and Mn helices, respectively. The latter have also relevant next-nearest-neighbor Mn-Mn antiferromagnetic interactions (of ∼6 meV). Co sites are characterized by noncollinear uniaxial anisotropies, whereas Mn sites are rather isotropic. A key result pertains to the Co helix: The microscopic picture resulting from density-functional calculations allows us to propose a spin Hamiltonian of increased complexity with respect to the commonly employed Ising Hamiltonian, suitable for the study of finite-temperature behavior, and that seems to clarify the puzzling scenario of multiple characteristic energy scales observed in experiments.
Combined first-principles and thermodynamic approach toM-nitronyl nitroxide(M= Co, Mn) spin helices / Scarrozza, Marco; Vindigni, Alessandro; Barone, Paolo; Sessoli, Roberta; Picozzi, Silvia. - In: PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS. - ISSN 1098-0121. - STAMPA. - 91:(2015), pp. 1-15. [10.1103/PhysRevB.91.144422]
Combined first-principles and thermodynamic approach toM-nitronyl nitroxide(M= Co, Mn) spin helices
SESSOLI, ROBERTA;
2015
Abstract
The properties of two molecular-based magnetic helices, composed of 3d metal Co and Mn ions bridged by nitronyl nitroxide radicals, are investigated by density-functional calculations. Their peculiar and distinctive magnetic behavior is here elucidated by a thorough description of their magnetic, electronic, and anisotropy properties. Metal ions are antiferromagnetically coupled with the radicals, leading to a ferrimagnetically ordered ground state. A strong metal-radical exchange coupling is found, about 44 and 48 meV for Co and Mn helices, respectively. The latter have also relevant next-nearest-neighbor Mn-Mn antiferromagnetic interactions (of ∼6 meV). Co sites are characterized by noncollinear uniaxial anisotropies, whereas Mn sites are rather isotropic. A key result pertains to the Co helix: The microscopic picture resulting from density-functional calculations allows us to propose a spin Hamiltonian of increased complexity with respect to the commonly employed Ising Hamiltonian, suitable for the study of finite-temperature behavior, and that seems to clarify the puzzling scenario of multiple characteristic energy scales observed in experiments.File | Dimensione | Formato | |
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