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Evidence for a Reorientation Transition in the

Phase Behaviour of a Two-Dimensional Dipolar

Antiferromagnet

ByAbdel-Rahman M. Abu-Labdeh

An-Najah National University, PalestineCollaborated by

John Whitehead, MUN-Canada

Keith De’Bell, UNB-Canada

Allan MacIsaac, UWO-Canada

Supported by

MUN & NSERC of Canada

May 8, 2007

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Outline

1. Introduction

a. Definitions

b. Motivation

c. Aim

2. The Model in General Terms

3. Monte Carlo Method

4. Results

5. Summary 2

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  Definitions

Magnetism results from the  Spin and orbital degrees of freedom of the

electron Magnetism is influenced by the

1.  Structure2.Composition3.Dimensionality of the system

Magnetic materials can be divided into1.Bulk2.Low-dimensional (Quasi-2D)

a. Ultra thin magnetic filmsb. Layered magnetic compounds (e.g., REBa2Cu3O7-δ)

c. Arrays of micro or nano-magnetic dots

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  Motivation  Quasi-2D spin systems have received much greater

attention due to

1.  Their magnetic properties

2. Their significant advances in technological applications such as

a. Magnetic sensors

b. Recording

c. Storage media

  Few systematic work have done on the quasi-2D

 antiferromagnetic systems. In particular, having  Exchange  Dipolar  Magnetic surface anisotropy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Aim   Is to obtain a better understanding of the quasi -2D

antiferromagnetic systems

  To achieve this aim

  Results from Monte Carlo simulations are pre

sented for a 2D classical Heisenberg system on

a square lattice (322 , 642 , 1042 )

  Including

 Antiferromagnetic Exchange interaction

Long-range dipolar interaction

Magnetic surface anisotropy

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The Model in General Terms 

 

  

 )1)

where

{σi } is a set of three-dimensional classical vec

  tors of unit magnitude

 g is the strength of the dipolar interaction

J is the strength of the exchange interaction

K, is the strength of the magnetic surface anisotropy

 . In this study  K≤ 0 J / 9 = -10

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Monte Carlo Method1. Constructing an infinite plane from replicas of a finite

system

2. Using the Ewald summation technique

3. Using the standard Metropolis algorithm

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Ground State

At the Transition:

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Definition of the Order Parameters

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The Order Parameters: J= -l0g, L=I04

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The Heat Capacity: J= -l0g, L=104

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The Magnetic Phase Diagram: J= -l0g

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The Magnetic Phase Diagram: J= -lOg

Hz=O, 10, 15g

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Summary The T magnetic phase diagram is established

for the 2D dipolar Heisenberg antiferromagnetic

system on a square lattice for J = -l0g This phase diagram shows A first-order reorientation transition from theparallel antiferromagnetic phase to the perpen dicular antiferromagnetic phase with

increasing

Applying an out-of-plane magnetic field causes

this phase boundary to be at lower values of

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Acknowledgements

MUN & NSERC for Financial Support

C3.ca for Access to Computational Resources

at

University of Calgary

Memorial University of Newfoundland

An-Najah National University

Conference Organizing Committee

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Thank You