Magnetic properties of 2D nano-islands II: Ising spin model with out-of-plane magnetic field

M. Abou Ghantous, A. Khater

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

An Ising effective field theory model is presented to calculate the magnetic properties of 2D nano-islands on a nonmagnetic substrate, subject to an externally out-of-plane applied magnetic field. The system Hamiltonian contains nearest neighbor exchange interactions, single-atom magnetic anisotropies, and the Zeeman term. The calculations yield, in particular, the single site spin correlations, the magnetizations, and the isothermal susceptibilities, for the core and periphery domains of the nano-island. The choice of a spin S=1 for the atoms of the system permits the analysis of local spin fluctuations via the single site spin correlations. We investigate in this respect the effects due to the different magnetocrystalline anisotropies and reduced dimensionalities, for the core and periphery domains, and in particular the critical influence of the applied magnetic field. Detailed theoretical results are presented for the square and hexagonal lattice symmetries, with numerical applications for the 2D monolayer Co nano-islands on a Pt substrate. It is shown that the remarkable differences between the magnetic properties of the core and periphery domains in zero field are washed out when an out-of-plane field is applied. The applied field also provokes critical discontinuities for the spin correlations and magnetization reversals, for the core and periphery domains, which are especially evident for the hexagonal lattice nano-island in the range of fields of interest. The discontinuities and magnetization reversals occur over elementary temperature widths, and shift to lower temperatures with increasing field. The field-dependant isothermal susceptibilities show new features very different from those for the susceptibilities in zero field. The present Ising model does not show any blocking temperature transition to superparamagnetism.

Original languageEnglish
Pages (from-to)2504-2512
Number of pages9
JournalJournal of Magnetism and Magnetic Materials
Volume323
Issue number20
DOIs
Publication statusPublished - Oct 2011
Externally publishedYes

Fingerprint

Magnetization reversal
Magnetic properties
Superparamagnetism
Magnetic fields
magnetic properties
Magnetocrystalline anisotropy
Hamiltonians
Spin fluctuations
Atoms
Ising model
Magnetic anisotropy
Exchange interactions
Substrates
magnetic fields
Superconducting transition temperature
Monolayers
Magnetization
magnetic permeability
magnetization
discontinuity

Keywords

  • Ising spin model
  • Magnetic properties of nano-island
  • Magnetization reversal
  • Nano-islands in magnetic field

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electronic, Optical and Magnetic Materials

Cite this

Magnetic properties of 2D nano-islands II : Ising spin model with out-of-plane magnetic field. / Abou Ghantous, M.; Khater, A.

In: Journal of Magnetism and Magnetic Materials, Vol. 323, No. 20, 10.2011, p. 2504-2512.

Research output: Contribution to journalArticle

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AB - An Ising effective field theory model is presented to calculate the magnetic properties of 2D nano-islands on a nonmagnetic substrate, subject to an externally out-of-plane applied magnetic field. The system Hamiltonian contains nearest neighbor exchange interactions, single-atom magnetic anisotropies, and the Zeeman term. The calculations yield, in particular, the single site spin correlations, the magnetizations, and the isothermal susceptibilities, for the core and periphery domains of the nano-island. The choice of a spin S=1 for the atoms of the system permits the analysis of local spin fluctuations via the single site spin correlations. We investigate in this respect the effects due to the different magnetocrystalline anisotropies and reduced dimensionalities, for the core and periphery domains, and in particular the critical influence of the applied magnetic field. Detailed theoretical results are presented for the square and hexagonal lattice symmetries, with numerical applications for the 2D monolayer Co nano-islands on a Pt substrate. It is shown that the remarkable differences between the magnetic properties of the core and periphery domains in zero field are washed out when an out-of-plane field is applied. The applied field also provokes critical discontinuities for the spin correlations and magnetization reversals, for the core and periphery domains, which are especially evident for the hexagonal lattice nano-island in the range of fields of interest. The discontinuities and magnetization reversals occur over elementary temperature widths, and shift to lower temperatures with increasing field. The field-dependant isothermal susceptibilities show new features very different from those for the susceptibilities in zero field. The present Ising model does not show any blocking temperature transition to superparamagnetism.

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