## Abstract

We report a combined experimental and theoretical study of the spin S=12 nanomagnet Cu_{5}(OH)_{2}(NIPA)_{4}·10H _{2}O (Cu_{5}-NIPA). Using thermodynamic, electron spin resonance, and 1H nuclear magnetic resonance measurements on one hand, and ab initio density-functional band-structure calculations, exact diagonalizations, and a strong-coupling theory on the other, we derive a microscopic magnetic model of Cu_{5}-NIPA and characterize the spin dynamics of this system. The elementary fivefold Cu2^{+} unit features an hourglass structure of two corner-sharing scalene triangles related by inversion symmetry. Our microscopic Heisenberg model comprises one ferromagnetic and two antiferromagnetic exchange couplings in each triangle, stabilizing a single spin S=12 doublet ground state (GS), with an exactly vanishing zero-field splitting (by Kramers' theorem), and a very large excitation gap of Δâ‰ 68 K. Thus, Cu_{5}-NIPA is a good candidate for achieving long electronic spin relaxation (T_{1}) and coherence (T_{2}) times at low temperatures, in analogy to other nanomagnets with low-spin GS's. Of particular interest is the strongly inhomogeneous distribution of the GS magnetic moment over the five Cu2^{+} spins. This is a purely quantum-mechanical effect since, despite the nonfrustrated nature of the magnetic couplings, the GS is far from the classical collinear ferrimagnetic configuration. Finally, Cu_{5}-NIPA is a rare example of a S=12 nanomagnet showing an enhancement in the nuclear spin-lattice relaxation rate 1/T_{1} at intermediate temperatures.

Original language | English (US) |
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Article number | 214417 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 87 |

Issue number | 21 |

DOIs | |

State | Published - Jun 14 2013 |

## All Science Journal Classification (ASJC) codes

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics