Molecular Magnets

Molecular magnetism is an interdisciplinary research area, which deals with design, synthesis and physical characterization as well as the theoretical modeling of molecular materials showing acquired properties. The features that distinguish molecular magnets from traditional magnetic materials are: low-density, transparency to electromagnetic radiation, and sensitivity to external stimuli such as light, pressure, temperature, chemical modification or magnetic/electric field. Furthermore, molecular magnetism offers an exceptional collection of materials of various magnetic dimensionality: from 0D single-molecule magnets and 1D single-chain magnets, regarded as molecular nanomagnets due to slow relaxation and bistability at low temperatures, through 2D molecular layers, to 3D coordination polymers showing the collective ordering of magnetic moments below the critical temperature Tc. Research into molecule-based materials, both theoretical and experimental became more intense at the end of 20th century and has concentrated on (i) low dimensional materials, motivated by their potential applicability in high-density magnetic storage or nanoscale devices and (ii) on “functional” materials, strongly responding to change in external parameters, that may be used in sensors of a different type. This Special Issue shows the rich palette of the properties of magnetic molecular materials and presents current work on this interesting and important topic. The issue contains four review articles and also includes the results by the authors, as well as original contributed papers. Molecular magnets involve well-localized magnetic moments, which make them the perfect playground for the investigation of intriguing phenomena and testing theoretical models. The interplay of spatial anisotropy of the exchange coupling and the intrinsic or magnetic-field induced spin anisotropy were discussed in the two-dimensional magnetic models by Orendáčová et al. [1]. In this excellent review, authors provide a concise introduction of the development of the theory and numerical approaches aimed at the description of low-dimensional magnetism. The main body of this paper presents a thorough study of the ground state and finite-temperature properties of the S = 1⁄2 models interpolating between the quantum Heisenberg antiferromagnetic chain and the rectangular spin lattice. The effect of the possible inter-layer exchange coupling resulting in the stabilization of the 3D long-range order is also discussed. Some physical consequences following from the characteristics of the underlying model are evidenced by reporting consistent experimental data on magnetic and calorimetric properties of low-dimensional Cu(II) based metal-organic magnets. A complete understanding of the mechanisms of the magnetic interaction in molecular magnets requires advanced calculations such as proposed by Brumfield and Haraldsen in [2]. Based on the Heisenberg spin-spin exchange model, the general relationships for the quantum energy levels, the spin states for isosceles spin trimmers of spins equal 1⁄2 up to 5/2 are provided. Dependence on heat capacity, magnetic susceptibility on temperature, and the corresponding inelastic neutron scattering structure factors have been determined. As stated by the authors, results of the calculations could help with the general analysis and characterization of magnetic molecule-based systems. The influence of external pressures on the structural and magnetic properties of molecular magnets has been reviewed by Zentkova and Mihalik [3]. The underlying mechanisms of the effect are presented on the example of Cr(CN)6-based Prussian blue analogues (PBs)—TM-Cr(CN)6 and