Insights into Nature of Magnetization Plateaus of a Nickel Complex [Ni4(μ-CO3)2(aetpy)8](ClO4)4 from a Spin-1 Heisenberg Diamond Cluster

Abstract

Magnetic and magnetocaloric properties of a spin-1 Heisenberg diamond cluster with two different coupling constants are investigated with the help of an exact diagonalization based on the Kambe’s method, which employs a local conservation of composite spins formed by spin-1 entities located in opposite corners of a diamond spin cluster. It is shown that the spin-1 Heisenberg diamond cluster exhibits several intriguing quantum ground states, which are manifested in low-temperature magnetization curves as intermediate plateaus at 1/4, 1/2, and 3/4 of the saturation magnetization. In addition, the spin-1 Heisenberg diamond cluster may also exhibit an enhanced magnetocaloric effect, which may be relevant for a low-temperature refrigeration achieved through the adiabatic demagnetization. It is evidenced that the spin-1 Heisenberg diamond cluster with the antiferromagnetic coupling constants J1/kB = 41.4 K and J2/kB = 9.2 K satisfactorily reproduces a low-temperature magnetization curve recorded for the tetranuclear nickel complex [Ni4(μ-CO3)2(aetpy)8](ClO4)4 (aetpy = 2-aminoethyl-pyridine) including a size and position of intermediate plateaus detected at 1/2 and 3/4 of the saturation magnetization. A microscopic nature of fractional magnetization plateaus observed experimentally is clarified and interpreted in terms of valence-bond crystal with either a single or double valence bond. It is suggested that this frustrated magnetic molecule can provide a prospective cryogenic coolant with the maximal isothermal entropy change −ΔSM=10.6 J·K−1·kg−1 in a temperature range below 2.3 K.

On the Magnetization and Entanglement Plateaus in One-Dimensional Confined Molecular Magnets

“…As we will show in the next sections, representative magnetic/entanglement properties are extracted from spin chains formed by 6-12 trimers, i.e., 18-36 S = 1 local spin sites. Such systems represent a Hilbert space dimension that is too large to perform full diagonalization, unpractical for analytical methods that could solve specific parts of the configurational space considered here [31] and difficult to treat using Monte Carlo methods due to the local and clustered frustrations present here [12,38,39].…”

“…The aforementioned molecules revealed qualitatively different tunneling features from typical molecular magnets, such as Mn 12 acetate or Fe 8 [1,2,5]. For example, Ni 4 has no tunneling in a zero magnetic field, and the electron paramagnetic-resonance EPR spectra exhibited unusual double sets of low-temperature peaks corresponding to slightly different easy magnetization axes [31]. Unlike Mn 12 acetate and Mn 4 dimer or Fe x (x = 4, 8), encapsulated Ni molecular magnets seemed not to be equally spaced from each other [31,33] and did not have effective giant spins.…”

“…For example, Ni 4 has no tunneling in a zero magnetic field, and the electron paramagnetic-resonance EPR spectra exhibited unusual double sets of low-temperature peaks corresponding to slightly different easy magnetization axes [31]. Unlike Mn 12 acetate and Mn 4 dimer or Fe x (x = 4, 8), encapsulated Ni molecular magnets seemed not to be equally spaced from each other [31,33] and did not have effective giant spins. Furthermore, the couplings of Cr-Ni molecular rings were studied by using different ligand-transition metal bridges, and the different sizes of the ligands could tailor the intermolecular interactions in Ni-based molecules as well [32,34,35].…”

“…Here, we focus on 1D systems resulting from the coupling of several SMMs with quasione-dimensional exchange-interaction topologies that mimic their encapsulation by using carbon nanotubes, as recently achieved by Domanov et al [26]. Encapsulation, embedding, and/or tailored confinement/deposition of molecular magnets is a cutting-edge path in SMM-based material prototypes [27][28][29] and, in particular, several Ni-based molecules have been synthesized from similar methods so far [26,[30][31][32]. The aforementioned molecules revealed qualitatively different tunneling features from typical molecular magnets, such as Mn 12 acetate or Fe 8 [1,2,5].…”

Robust quantum entanglement and teleportation in the tetrapartite spin-1/2 square clusters: Theoretical study on the effect of a cyclic four-spin exchange

“…The groundstate phase diagram of the model involves two localized one spin-down phases, |ψ 11 and |ψ 13 , the localized two spin-up phase |ψ 5 and the fully polarized phase |ψ 15 . These ground states can be represented by the form |S T , S AB , S CD [58,59] as…”