Miguel A. Novak

The molecular approach to nanoscale magnetism

Abstract Molecular clusters of paramagnetic metal ions have been widely investigated as model for magnetism at the nanoscale, especially for quantum effects like the tunneling of the magnetic moment. We present here some recent results obtained on derivatives of the well-known Mn12 cluster, especially on the half-integer spin compounds. The role of the transverse anisotropy in the dynamics of the magnetization is here elucidated through the comparison of the tunneling rate of the magnetization in two Fe8 cluster compounds, which differ only in the transverse anisotropy. Local dipolar fields and nuclear hyperfine fields have also revealed to strongly affect the relaxation in the pure tunneling regime and recent experiment has allowed to determine the intrinsic linewidth of the tunneling resonance. The transverse field dependence of the relaxation rate of Fe8 has revealed oscillations that are analog to the topological constructive–destructive interference of the spin phase (Berry phase) and we review here some very recent results. The magnetic behavior of antiferromagnetic ring-shaped clusters is also discussed for their potential interest as models for antiferromagnetic particles. Some recent results obtained by other chemists in the synthesis of large spin clusters are also reviewed.

Finite-size effects in single chain magnets: an experimental and theoretical study.

The problem of finite-size effects in s=1/2 Ising systems showing slow dynamics of the magnetization is investigated introducing diamagnetic impurities in a Co2+-radical chain. The static magnetic properties have been measured and analyzed considering the peculiarities induced by the ferrimagnetic character of the compound. The dynamic susceptibility shows that an Arrhenius law is observed with the same energy barrier for the pure and the doped compounds while the prefactor decreases, as theoretically predicted. Multiple spin reversal has also been investigated.

Temperature dependence of the coercive field in single-domain particle systems

The magnetic properties of

Glauber slow dynamics of the magnetization in a molecular Ising chain

{\mathrm{Cu}}_{97}{\mathrm{Co}}_{3}

A Cobalt Pyrenylnitronylnitroxide Single‐Chain Magnet with High Coercivity and Record Blocking Temperature

and

Magnetic properties of a Mn cluster organic compound

{\mathrm{Cu}}_{90}{\mathrm{Co}}_{10}

New Families of Hetero-tri-spin 2p−3d−4f Complexes: Synthesis, Crystal Structures, and Magnetic Properties

granular alloys were measured over a wide temperature range

Structure and morphology of spinel MFe2O4 (M=Fe, Co, Ni) nanoparticles chemically synthesized from heterometallic complexes.

(2\char21{}300\phantom{\rule{0.3em}{0ex}}\mathrm{K})

A single-chain magnet with a very high blocking temperature and a strong coercive field.

. The measurements show an unusual temperature dependence of the coercive field. A generalized model is proposed and explains well the experimental behavior over a wide temperature range. The coexistence of blocked and unblocked particles for a given temperature raises difficulties that are solved here by introducing a temperature dependent blocking temperature. An empirical factor gamma

Crystal Structure and Magnetic Properties of a New Chiral Manganese(II) Three-Dimensional Framework: Na3[Mn3(HCOO)9]

(\ensuremath{\gamma})