Phase transition and spin dynamics in the two-dimensional easy-plane ferromagnet

Pires, A.S.T.; Gouvêa, M. E.

doi:10.1103/physrevb.48.12698

Cited by 37 publications

(40 citation statements)

References 22 publications

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“…5 was obtained for 0 10 δ = . , but the results for all δ in the (0 0 25) , . range are qualitatively equivalent.…”

Section: Jmentioning

confidence: 93%

One‐dimensional XY antiferromagnetic Heisenberg model with nearest and next nearest neighbour exchange interactions

Gouvêa¹,

Pires²

2005

Physica Status Solidi (b)

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We study the one-dimensional anisotropic antiferromagnetic Heisenberg model with competing interactions using the self-consistent harmonic approximation. The dispersion relation, the correlation function and the susceptibility are obtained for several values of the ratio 2 1 J J δ = / between the nearest ( 1 J ) and next nearest neighbour exchange interactions ( 2 J ). For 0 25 δ < . , the pair correlation function decays monotonically and exponentially to zero and the susceptibility has a maximum value at π q = . For, the exponential decay of the pair correlation is modified by an oscillatory behavior while the maximum of the susceptibility does not necessarily occur at π q = . Furthermore, the phase diagram of a system with weakly coupled chains is considered.

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“…5 was obtained for 0 10 δ = . , but the results for all δ in the (0 0 25) , . range are qualitatively equivalent.…”

Section: Jmentioning

confidence: 93%

One‐dimensional XY antiferromagnetic Heisenberg model with nearest and next nearest neighbour exchange interactions

Gouvêa¹,

Pires²

2005

Physica Status Solidi (b)

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“…In the classical limit ( 5 ) becomes [5] e = [1 -@Z(i)l exp (-e/e), (6) where and 0 = T/zJS', with z being the number of nearest-neighbor sites. Equation (6) is a self-consistent equation giving e for each temperature.…”

Section: (4)mentioning

confidence: 99%

Exchange Renormalization and Phase Transition in the Classical Three‐Dimensional Anisotropic Ferromagnet

Pires

1994

Physica Status Solidi (b)

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The O(2) ( = XU) model has the interesting and important feature that it supports topological excitations which in two dimensions are vortices. By now the Kosterlitz-Thouless transition in 2d is quite well understood [l].The three-dimensional O(2) classical Heisenberg model (planar model) is known to have a second-order phase transition at TJJ = 2.17 from an ordered phase with nonzero magnetization to a disordered phase [2]. Banks and Myerson [3] have shown that above the critical temperature the effective potential for this model becomes linear, guaranteeing exponential fall-off of the correlation function. They postulated then that the mechanism which forces the potential to become linear was the appearance for large enough temperature of vortex rings whose size would grow without limit, the long vortex rings destroying the long-range spin-spin correlations. They estimated the upper bound for T,, using the Villain approximation, as TJJ z 6.3.Recently, Kohring et al.[4] using Monte Carlo techniques have shown that vortex strings are responsible for the phase transition in the three-dimensional planar model. However, the task of taking these topological excitations into account, as Kosterlitz-Thouless theory did for the two-dimensional O(2) model, remains an open problem.In this note we will extend a self-consistent approximation, developed to study the two-dimensional model [5], to study the classical 3D anisotropic ferromagnet with nearest-neighbor interaction, described by the following Hamiltonian:where J > 0, S,. is a classical spin, Y + u labels the six nearest-neighbor sites of Y in a simple cubic lattice (or eight in a body-centered lattice) and 0 5 , I < 1 describes an exchange easy-plane anisotropy.The classical XY model is given by (1) with i = 0, but considering S, = (S:, Sy, S:). The planar rotator model has a Hamiltonian of the same form, but the spins have only two components, S,. = (S:, Sy).In order to use the self-consistent approximation we start by writing Hamiltonian (1) in terms of the polar representation for the spin at site Y, *) CP 702, 30.161-970 Belo Horizonte, MG Brazil. ') Partially supported by CNPq and FINEP, Brazil.

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“…The model exhibits a standard order-disorder phase transition in dimensions d42, while it undergoes a topological phase transition, the well known Kosterlitz-Thouless transition, in d =2 [3].…”

Section: Introductionmentioning

confidence: 99%

“…The stiffness takes into account anharmonic terms (in the oneloop approximation) in the expansion of cosðj n À j n þ d Þto all orders [3]. Taking the Fourier transform of (11) we obtain:…”

Section: Introductionmentioning

confidence: 99%

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Spin transport in the anisotropic easy-plane two-dimensional Heisenberg antiferromagnet

Pires

Lima

2010

Journal of Magnetism and Magnetic Materials

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a b s t r a c tSpin transport in the easy-plane two-dimensional anisotropic Heisenberg antiferromagnet with S= 1 is studied. Regular part of spin conductivity is calculated, at zero temperature, using a self-consistent harmonic approximation and the Kubo formalism. Three magnon processes provide the dominant contribution to the spin conductivity. Furthermore, the transport is ballistic and characterized by finite Drude weight.

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Phase transition and spin dynamics in the two-dimensional easy-plane ferromagnet

Cited by 37 publications

References 22 publications

One‐dimensional XY antiferromagnetic Heisenberg model with nearest and next nearest neighbour exchange interactions

One‐dimensional XY antiferromagnetic Heisenberg model with nearest and next nearest neighbour exchange interactions

Exchange Renormalization and Phase Transition in the Classical Three‐Dimensional Anisotropic Ferromagnet

Spin transport in the anisotropic easy-plane two-dimensional Heisenberg antiferromagnet

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