Low-Temperature Magnetocaloric Properties of V12 Polyoxovanadate Molecular Magnet: A Theoretical Study

Abstract

The paper presents a computational study of the magnetocaloric properties of the V12 polyoxovanadate molecular magnet. The description is restricted to low-temperature range (below approximately 100 K), where the magnetic properties of the system in question can be sufficiently modelled by considering a tetramer that consists of four vanadium ions with spins S=1/2. The discussion is focused on the magnetocaloric effect in the cryogenic range. The exact and numerical diagonalization of the corresponding Hamiltonian is used in order to construct the thermodynamic description within a version of the canonical ensemble. The thermodynamic quantities of interest, such as magnetic entropy, specific heat, entropy change under isothermal magnetization/demagnetization, temperature change under adiabatic magnetization/demagnetization, refrigerant capacity, and magnetic Grüneisen ratio, are calculated and discussed extensively. The importance of two quantum level crossings for the described properties is emphasized. The significant ranges of direct and inverse magnetocaloric effect are predicted. In particular, the maximized inverse magnetocaloric response is found for cryogenic temperatures.

Effect of Single-Ion Anisotropy on Magnetocaloric Properties of Frustrated Spin-s Ising Nanoclusters

“…The experiment revealed isentropes with a rich structure, which were very well reproduced theoretically by considering a simple Heisenberg spin Hamiltonian with only exchange [17] or including also intramolecular dipolar interactions [18]. The observed isentropes were concluded to be a direct manifestation of the trigonal antiferromagnetic net structure, which triggered further experimental [19,20] and theoretical [21][22][23][24][25][26][27][28][29][30][31] studies of mainly frustration-enhanced MCE in finite systems of various shapes and topologies. They included geometrically frustrated Ising spin clusters with shapes of regular polyhedra [21,22] or triangular geometry [23][24][25][26][27].…”

Two-spin and multi-spin quantum entanglement in V12 polyoxovanadate molecular nanomagnet

“…In the present work, we use the following, most general Hamiltonian of the anisotropic antiferromagnetic Heisenbergtype model for a tetramer composed of spins S = 1/2 to model the low-temperature properties of V12 [6,7,32]:…”

“…The form of the ground states and the expressions for the critical fields is given in Appendix A; see also the discussion in our work Ref. [32]).…”

“…The ground state with S = 0 in V12 is valid for the external magnetic fields below the first critical field B c,1 (for detailed discussion see Appendix A and also Appendix in our Ref. [32]).…”

“…The ground state with S = 1 is valid for the external magnetic fields between the first critical field B c,1 and the second critical field B c,2 (for detailed discussion see Appendix A and also Appendix in our Ref. [32]). Its form is given in Appendix A.4 (see also Ref.…”