Modeling molecular magnets with large exchange and on-site anisotropies

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

doi:10.1103/physrevb.98.214409

Cited by 3 publications

(3 citation statements)

References 42 publications

(34 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

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

Self Cite

View full text Add to dashboard Cite

show abstract

“…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

Self Cite

View full text Add to dashboard Cite

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]

show abstract

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

2020

Preprint

Self Cite

View full text Add to dashboard Cite

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 spin chains, each of six identical spins with nearest neighbour anisotropic exchange interactions. Each spin is also anisotropic with an axial anisotropy. The site spin on these short chains take values 1, 3/2 or 2. Using eigenstates of these short chains as the states of Markov chain, we carry out a kMC simulation starting with an initial state in which all chains are completely spin polarized and assembled so as to experience ferromagnetic spindipolar 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 behaviour for weak on-site interactions. The energy barrier to magnetization relaxation increases with 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, owing to the small size as well as large spin on the molecules.

show abstract

Modeling molecular magnets with large exchange and on-site anisotropies

Cited by 3 publications

References 42 publications

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

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

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

Contact Info

Product

Resources

About