Heisenberg-type ferromagnetic films with a sandwich structure

Kecer, J.; Ilkovič, V.

doi:10.2478/s11534-006-0026-x

Cited by 1 publication

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“…For the terms stemming from the single-ion anisotropy we have chosen the Anderson-Callen decoupling procedure [9] gives good results [10,11] for the magnetization if the anisotropy parameter K 2 is much smaller than the parameter of the exchange coupling. Using the eigenvector method (EVM) described, for example, in [12][13][14] we obtain after a two-dimensional Fourier transform to momentum space, the L coupled equations of motion for Green's functions G (l) νµ (q, ω) of layer labeled by µ. By using the spectral theorem, for the spontaneous magnetization per site in each atomic layer of the film with spin S we obtain…”

Section: Model and Methodsmentioning

confidence: 99%

Quantum Model for Ferromagnetic Thin Films with an Alternating Crystal Field

Kecer

Tuleja²

2008

Acta Phys. Pol. A

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Within the framework of many-body Green's function theory there are studied the properties of the quantum Blume-Capel model for ferromagnetic films with an alternating single-ion anisotropy on the odd atomic layers and on the even ones. We analyse various possible phase diagrams for the surface exchange couplings and the single-ion anisotropy parameters. Model and methodThe ferromagnetic Blume-Capel-Ising (BCI) model has been studied within the mean field approximation [1], the effective field theory [2], the two-spin cluster approximation in the cluster expansion method [3,4], Monte Carlo simulations [5], a thermodynamically self-consistent theory based on an Ornstein-Zernike approximation [6], the exact solution based on the Bethe lattice by means of the exact recursion relations [7]. Most of the studies mentioned above displays also the existence of a tricritical point at which the phase transition changes from second order to first order when the value of K 2 becomes negative. Our work represents the first atempt to consider a quantum version of BCI model. Within quantum Blume-Capel (QBC) model we will study the influence of the enhancement of the surface exchange coupling and the alternative single-ion anisotropy K 2 (1) on the odd atomic layers and K 2 (2) on the even ones on the critical behaviour of thin ferromagnetic films.The Hamiltonian of the considered system consists a Heisenberg exchange interaction with strength J ij > 0 between nearest neighbour lattice sites, an exchange anisotropy with strength D > 0, and a second-order single-ion anisotropy with strength K 2 > 0: (197)

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