![]() The calculations become more even more demanding when structures involving high number of spins, especially S > 1 / 2, are modeled. Exact studies of Heisenberg model for particular molecular systems can also be found in the literature, e.g., a butterfly-shaped structure with higher spin or our previous study concerning a structure with two interacting triangles. In addition to classical Ising model-based studies, quantum Heisenberg model has also been investigated by exact methods in the context of zero-dimensional cluster geometry, e.g., cube, a cuboctahedron, an edge-sharing tetrahedron, a hexagon, or a finite chain clusters. The exactly studied geometries include regular Ising polyhedra, planar Ising clusters based on the triangular lattice, or Ising clusters based on tetrahedra. Therefore, in the context of the theoretical modeling of magnetic entropy and magnetocaloric properties of zero-dimensional systems, numerous works concerning spin clusters of various geometry can be mentioned first, especially those for spins 1/2. For systems consisting of low enough number of spins, the exact methods for spin Hamiltonians can be applied. To understand and control MCE in molecular magnets, the development of theoretical models for description of their thermodynamics is of key importance. These facts strongly motivate the interest in magnetocaloric properties of molecular magnets. In addition, such ideas as rotational MCE exploiting strong magnetic anisotropy are investigated in molecular systems. Another interesting route is utilizing the quantum level crossings. On the other hand, the maximization of MCE is searched in systems with magnetic frustration resulting from the interplay between the antiferromagnetic interactions and the geometry, where the relatively small changes of magnetic field can cause large variations of the magnetic entropy by lifting the quantum state degeneracy. Molecular magnets may offer record-high spin per molecule maximizing the potential span of entropy change, turning the attention to high spin clusters. The quest for cooling efficiency stimulates the development of various approaches to design molecular magnets with desired properties. The molecular nanomagnets proved their potential in subkelvin cooling and might be useful for on-chip cooling of nanoelectronic devices. One of their unique features is the direct applicability in nanoscale cooling. This focuses the attention on molecular magnets as highly promising materials. ![]() ![]() The constant quest for optimized materials for exploiting MCE motivates studies of novel relevant materials. Therefore, MCE is a phenomenon of paramount importance for advanced and innovative cooling in diverse temperature ranges, from room temperature in everyday use to subkelvin range for experimental devices, which becomes a crucial technological challenge. MCE consists in the dependence of the entropy of substance on the external magnetic field and thus allows designing of a thermodynamic cycle for refrigeration (working between two constant temperatures) or outlining the procedure used to lower the temperature. Among them, the magnetic cooling based on the magnetocaloric effect (MCE) should be emphasized as particularly interesting application. On the other hand, the possible multifunctionality of molecular magnets opens the way towards numerous applications. Zero-dimensional molecular nanomagnets offer the possibility of exploring a plethora of intriguing fundamental physical phenomena due to the underlying quantum physics. Molecular magnets constitute a highly interesting class of modern magnetic materials, the rapid development of which over the last decades required concerted effort of theoreticians and experimentalists. ![]()
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