Modelling magnetic anisotropy of single-chain magnets in |<i>d</i>/<i>J</i>| ≥ 1 regime

Haldar, Sumit; Raghunathan, Rajamani; Sutter, Jean‐Pascal; Ramasesha, S.

doi:10.1080/00268976.2017.1346832

Cited by 5 publications

(6 citation statements)

References 49 publications

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“…However, large quantum tunneling of magnetization leads to small hysteresis loops. In our previous studies [30], we have shown that large magnetic anisotropy of building blocks leads to breaking the spin symmetry. In this event associating a parent spin state to define the D M and E M parameters of a cluster is not possible due to intrusion of states from different parent spins within the given spin manifold.…”

Section: Introductionmentioning

confidence: 92%

Modeling molecular magnets with large exchange and on-site anisotropies

et al. 2018

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Spins in molecular magnets can experience both anisotropic exchange interactions and on-site magnetic anisotropy. In this paper we study the effect of exchange anisotropy on the molecular magnetic anisotropy both with and without on-site anisotropy. When both the anisotropies are small, we find that the axial anisotropy parameter DM in the effective spin Hamiltonian is the sum of the individual contributions due to exchange and on-site anisotropies. We find that even for axial anisotropy of about 15%, the low energy spectrum does not correspond to a single parent spin manifold but has intruders states arising from other parent spin. In this case, the low energy spectrum can not be described by an effective Hamiltonian spanning the parent spin space. We study the magnetic susceptibility, specific heat as a function of temperature and magnetization as a function of applied field to characterize the system in this limit. We find that there is synergy between the two anisotropies, particularly for large systems with higher site spins.

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Section: Introductionmentioning

confidence: 92%

Modeling molecular magnets with large exchange and on-site anisotropies

et al. 2018

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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%

“…In the Raman process, the intermediate vibrational state is a virtual state and is hence a higher-order quantum process. The inverse relaxation time in a one-phonon or direct process is linearly dependent on temperature, while that in a Raman process depends on the ninth power of temperature (T 9 ), and the Orbach process has an exponential dependence on temperature. Spin-spin relaxation mechanisms consider both the hyperfine and dipolar interaction terms.…”

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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“…The SMMs are characterized by exchange interactions between magnetic centers which are often frustrated 21 . There have been many theoretical studies in SMMs and SCMs and the role of on-site anisotropies and exchange anisotropies in determining the overall magnetic anisotropy of the SMMs and SCMs 22,23 . The overall magnetic anisotropy is expected to control the blocking temperature T B of the system.…”

Section: Introductionmentioning

confidence: 99%

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

Haldar

Ramasesha

2020

Journal of Magnetism and Magnetic Materials

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We study the magnetocaloric effect (MCE) in spin clusters of six spins with site spins s = 1, 3/2 and 2 for different exchange anisotropies. We also study MCE in an assembly of spin clusters, on a chain, a 2-D square lattice and a 3-D cubic lattice with spin-dipolar interactions using a Monte Carlo method in spin-1 systems. We compute the magnetic Grüneisen parameter Γ H , and study its dependence on exchange anisotropy and spin-dipolar interaction. With increase of exchange anisotropy the maxima in Γ H , shifts to higher magnetic fields and becomes a sharp singularity. The first maximum in Γ H shifts to lower fields as we increase spin-dipolar interaction. The behaviour of Γ H on applied magnetic field is also reflected in the magnetic entropy of the systems. The first maximum in Γ H also shifts to lower magnetic field strength as the magnitude of the site spin increases. We also show the dependence of Γ H on dimensionality of the lattice for a fixed lattice constant.arXiv:1910.07085v1 [cond-mat.str-el]

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Modelling magnetic anisotropy of single-chain magnets in |d/J| ≥ 1 regime

Cited by 5 publications

References 49 publications

Modeling molecular magnets with large exchange and on-site anisotropies

Modeling molecular magnets with large exchange and on-site anisotropies

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

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

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