A study of magnetic properties using some theoretical models

Dissertant

Khidr, Diya Khalid

Thesis advisor

Abbud, sad

University

University of Technology

Faculty

-

Department

Applied Sciences Department

University Country

Iraq

Degree

Ph.D.

Degree Date

2009

English Abstract

In this work, the occurrence of spatially modulated structure in several competing interactions are examined.

Of particular interest are the situations where, for given values of the interactions.

The ground state is infinitely degenerate.

Most of the work presented here concerns the analysis of how this zero-temperature multidegeneraey can be removed by the interaction of weak perturbations such as spin anisotropy, external magnetic fields, or quantum fluctuations.

Many different studies of ferromagnetism and anti-ferromagnetism models have presented theories on energy minimization.

These studies, however, do not give visual confirmation of what is occurring during minimization.

One wish t-o study how the energy minimizes locally in a ferromagnetic system.

Where does the energy dissipate once the magnetic field is applied? Arc there regions that exhibit a chaotic nature before eventually aligning with an external magnetic field? It has been demonstrated that the energy of the system will minimize in the presence of an external magnetic field.

However, regions within the lattice may not converge at the same rate.

Our goal is to develop and apply a visual tool to the system, which would allow users to visualize the minimization process.

In this thesis, one describe a model and visualization system designed to illustrate the principles of energy minimization in ferromagnetic system.

Models of finite or semi-infinite chains of spins are considered where the competition between surface and the bulk effects creates adomain wall (kink) in ground state.

In this work, the aim is to discuss the role of a hitherto fore unexplored parameter on the unbinding transition : the spin anisotropy.

One should know that, as discrete spins with P-fold spin anisotropy soften, layering transitions can he stabilized in simple, short-range clock models, even at zero temperature (for P ≥ 3).

In particular, one can, in a chain of fcnomagnetically coupled (XY) spins.

Using an expansion in inverse spin anisotropy (l / D).

one can, calculating analytical solutions to the equilibrium equation () under the influence of a magnetic field for materials ferromagnetic and inti ferromagnetic, one can to rely on numerical methods that adopted is based on several programs as (Fortran Code 77, 90), and Chou-Griffiths algorithm method, to build the phase diagrams exhibits points where two multiphase lines meet at a first order transition.

When the spin anisotropy is infinite, one can calculate the energy differences, E-E, between neighboring interface states.

Then the special case P = 2 is considered, where the multidegeneracy cannot be Lifted for small values of I / D.

In this case we consider the quantum version of the model and show the quantum fluctuation can raise the inultidegeneracy stabilizing an infinite sequences of layering transition.

temperature Tr = 2.2 J / k, and ferromagnetic thin film from Nickel (N,) growth on cooper(Cu)at Curie temperature Tr = 2.112 J / k, in zero and nonzero magnetic field.

Main Subjects

Physics

Topics

• Magnetic properties

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305056