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arXiv · 1503.00292

A combined first-principles and thermodynamic approach to M-Nitronyl Nitroxide (M=Co, Mn) spin helices

Marco Scarrozza·Alessandro Vindigni·Paolo Barone·Roberta Sessoli·Silvia Picozzi
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Abstract

The properties of two molecular-based magnetic helices, composed of 3$d$ 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 meV and 48 meV for Co- and Mn-helices, respectively. The latter have also relevant next-nearest-neighbor Mn-Mn antiferromagnetic interactions (of $\sim$ 6 meV). Co-sites are characterized by non-collinear 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.

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Marco Scarrozza, Alessandro Vindigni, Paolo Barone, Roberta Sessoli, Silvia Picozzi. 2015-03-01. A combined first-principles and thermodynamic approach to M-Nitronyl Nitroxide (M=Co, Mn) spin helices. https://doi.org/10.1103/physrevb.91.144422

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