Magnetocaloric effect in molecular spin clusters and their assemblies: Exact and Monte Carlo studies using exact cluster eigenstates

Haldar, Sumit; Ramasesha, S.

doi:10.1016/j.jmmm.2020.166424

Cited by 12 publications

(6 citation statements)

References 30 publications

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“…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 [45], a cuboctahedron [46], an edge-sharing tetrahedron [47], a hexagon [48], or a finite chain [49] clusters. 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 [50] or our previous study concerning a structure with two interacting triangles [51].…”

Section: Introductionmentioning

confidence: 99%

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

Szałowski

Kowalewska

2020

Materials

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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.

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Section: Introductionmentioning

confidence: 99%

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

Szałowski

Kowalewska

2020

Materials

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“…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].…”

Section: Introductionmentioning

confidence: 54%

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

Mohylna

Žukovič

2020

Magnetochemistry

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Effects of a single-ion anisotropy on magnetocaloric properties of selected spin-s≥1 antiferromagnetic Ising clusters with frustration-inducing triangular geometry are studied by exact enumeration. It is found that inclusion of the single-ion anisotropy parameter D can result in a much more complex ground-state behavior, which is also reflected in a magnetocaloric effect (MCE) at finite temperatures. For negative D (easy-plane anisotropy) with increasing s, the ground-state magnetization as a function of the external field gradually shows increasing number of plateaus of various heights. Except for the cases of integer s with D<D0≤0, the first magnetization plateau is of non-zero height. This property facilitates an enhanced MCE in the adiabatic demagnetization process in the form of an abrupt decrease in temperature as the magnetic field vanishes to zero. The cooling rate can be considerably enhanced in the systems with larger s and D>0 (easy-axis anisotropy), albeit its dependence on these parameters is strongly dependent on the cluster geometry. From the studied systems more favorable conditions for observing a giant MCE were found in the 2CS cluster, consisting of two corner-sharing tetrahedra, the experimental realization of which could be technologically used for efficient refrigeration to ultra-low temperatures.

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“…The main focus of molecular magnetism has, therefore, been on raising the blocking temperature for magnetization relaxation by increasing the magnetic anisotropy barrier. Several earlier studies focused on analyzing the effect of on-site anisotropy as well as exchange anisotropy on the magnetic anisotropy barrier [8][9][10][11]. Single-chain magnets (SCMs) were subsequently synthesized, with the expectation that they will have a higher blocking temperature [12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Study of magnetization relaxation in molecular spin clusters using an innovative kinetic Monte Carlo method

Haldar

Ramasesha

2021

Phys. Rev. B

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Modeling blocking temperature in molecular magnets has been a long-standing problem in the field of molecular magnetism. We investigate this problem using a kinetic Monte Carlo (kMC) approach on an assembly of 100 000 short molecular magnetic chains (SMMCs), each of six identical spins with nearest-neighbor anisotropic ferromagnetic exchange interactions. Each spin is also anisotropic with an uniaxial anisotropy. The site spin on these SMMCs takes values 1, 3/2, or 2. Using the eigenstates of these SMMCs as the states of a Markov chain, we carry out a kMC simulation starting with an initial state in which all SMMCs are completely spin-polarized and assembled on a one-dimensional lattice so as to experience ferromagnetic spin-dipolar interaction with each other. From these simulations, we obtain the relaxation time τ r as a function of temperature and the associated blocking temperature. We study this for different exchange anisotropy, on-site anisotropy, and strength of dipolar interactions. The magnetization relaxation times show non-Arrhenius behavior for weak on-site interactions. The energy barrier to magnetization relaxation increases with an increase in on-site anisotropy, exchange anisotropy, and strength of spin dipolar interactions, more strongly on the last parameter. In all cases, the barrier saturates at large on-site anisotropy. The barrier also increases with site spin. The large barrier observed in rare-earth single ion magnets can be attributed to large dipolar interactions due to short intermolecular distances, due to their small size and large spin of the rare-earth ion in the molecule.

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Magnetocaloric effect in molecular spin clusters and their assemblies: Exact and Monte Carlo studies using exact cluster eigenstates

Cited by 12 publications

References 30 publications

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

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

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

Study of magnetization relaxation in molecular spin clusters using an innovative kinetic Monte Carlo method

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