Advanced quantum methods for the largest magnetic molecules

Journal of Magnetism and Magnetic Materials

2020

The paper presents a theoretical study of magnetocaloric properties of polyoxovanadate molecular magnet V6 containing 6 vanadium ions carrying quantum spins S = 1/2. The characteristic property of such structure is the presence of two weakly interacting spin triangles with all-antiferromagnetic couplings. The properties of the system are described using the exact numerical diagonalization approach applied to the quantum Heisenberg model and utilizing a field ensemble formalism. The dependence of the magnetic entropy and magnetic specific heat on the temperature and external magnetic field is calculated and extensively discussed. The magnetocaloric properties are quantified by isothermal entropy change and entropy derivative over the magnetic field. An interesting behaviour of isothermal entropy change is found, with high degree of tunability of the magnetocaloric effect with the initial and final magnetic field values.

Section: Introductionmentioning

confidence: 99%

Magnetocaloric properties of V6 molecular magnet

Journal of Magnetism and Magnetic Materials

2020

“…The calculations become more even more demanding when structures involving high number of spins, especially S > 1/2, are modeled. For this purpose, advanced and effective close-toexact approaches for thermodynamic description of the spin systems are developed [52][53][54][55].…”

Section: Introductionmentioning

confidence: 99%

Magnetocaloric Effect in Cu5-NIPA Molecular Magnet: A Theoretical Study

2020

Materials

We calculated the magnetocaloric properties of the molecular nanomagnet Cu5-NIPA, consisting of five spins S = 1 / 2 arranged in two corner-sharing triangles (hourglass-like structure without magnetic frustration). The thermodynamics of the system in question was described using the quantum Heisenberg model solved within the field ensemble (canonical ensemble) using exact numerical diagonalization. The dependence of the magnetic entropy and magnetic specific heat on the temperature and the external magnetic field was investigated. The isothermal entropy change for a wide range of initial and final magnetic fields was discussed. Due to plateau-like behavior of the isothermal entropy change as a function of the temperature, a high degree of tunability of magnetocaloric effect with the initial and final magnetic field was demonstrated.

“…We can mention that the theoretical studies of magnetization distribution (performed with either exact or approximate methods) are known in the literature both for zero-dimensional magnets [36] as well as for other non-uniform systems, like, for example, thin films [37][38][39]. Also the thermodynamics of magnetic clusters was subject of several computational works exploiting the exact (or close to exact) approaches, involving both 'classical', Isingbased systems [40][41][42][43][44][45] as well as highly non-trivial quantum Heisenberg systems [7,40,[46][47][48][49][50][51][52][53][54][55][56].…”

Section: Introductionmentioning

confidence: 99%

Magnetization distribution in a spin ladder-shaped quantum nanomagnet

Journal of Magnetism and Magnetic Materials

2019

The quantum nanomagnets show interesting site-dependent magnetic properties as a function of the temperature and the external magnetic field. In the paper we present the results of calculations for a finite quantum spin ladder with two legs, consisting of 12 spins S = 1/2, with open ends. We describe our system with isotropic quantum Heisenberg model and perform exact numerical diagonalization of the Hamiltonian to use canonical ensemble approach. Our analysis focuses on the site-dependent magnetization in the system, presenting magnetization distributions for various interaction parameters. We discuss extensively the temperature and magnetic field dependences of individual site magnetizations. The interesting behaviour, with pronounced non-uniformity of magnetization across the ladder, is found.