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Low-dimensional anisotropic Heisenberg ferromagnet with the magnetic properties of antiferromagnetic model

Author: SongChuangChuang
Tutor: ChenYuan
School: Guangzhou University
Course: Theoretical Physics
Keywords: Magnetic Properties Random phase approximation Anderson - Karen approximation Heisenberg model Green's function method
CLC: O482.52
Type: Master's thesis
Year: 2010
Downloads: 65
Quote: 0
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Abstract

With the advances in magnetic synthetic materials, synthetic materials, people can produce a magnetic interest, which is the low-dimensional quantum magnetism research has become a hot area of research, one of the reasons. From the study of matter and its formation mechanism of magnetic starting to explore new ways to improve the magnetic properties, to develop new applications magnetic field has become a contemporary magnetism main research methods and content. The study of magnetic process, resulting in a number of methods, but the comparison, the Green function method in the whole temperature region deal with the problem of the results obtained with the experimental and theoretical results match well with other, so that the method is magnetic substances present study better methods. In this article, we are using the Green function method to study low-dimensional anisotropic ferromagnetic and antiferromagnetic Heisenberg model. Green's function approach in the use of the system model, will produce high-end chain of equations of motion for the Green's function, which will require the use of means to cut off the approximate kinematic chain for cutting on the approximation, which can be a function of self-consistent equations. In this paper, we use the random phase approximation and Anderson - Karen approximation for Heisenberg ferromagnetic system for cutting approximation, while for Heisenberg antiferromagnet, we use random phase approximation to handle it. In both the system model, we get results with the results of others found better. The first chapter is the introduction. Describes the ferromagnetic and antiferromagnetic Heisenberg model of the background and content of this study, and the use of Green's function methods. Chapter II study exchange and single-ion anisotropy of the one-dimensional spin-1 Heisenberg ferromagnet magnetic properties. We use dual time Green's function method for processing the Hamiltonian of the system, has been advanced Green's function equations of motion, and then use the random phase approximation for the exchange anisotropy items for processing, but with Anderson - Karen approximation to deal with single-ion anisotropy term, resulting in a self-consistent equation of the Green's function, and finally by the spectral theorem to obtain magnetization on temperature, magnetic field and anisotropy parameters as a function of the relationship, and thus also to establish a critical temperature and magnetic susceptibility of temperature, magnetic field and anisotropy parameters of the functional relationship between. Later in this chapter, we have discussed the correlation length with temperature and anisotropy parameters. Our results with the results of other theoretical workers get a better match. The third chapter studies the case of high temperature and low-dimensional spin-1/2 Heisenberg antiferromagnet magnetic properties. In this chapter we still use the Green's function method to handle the antiferromagnetic Heisenberg model, using the random phase approximation for the exchange anisotropy items for processing. We mainly discussed the high-temperature and high-temperature field with no external field, as well as low temperatures, magnetization and magnetic susceptibility with temperature, the external field and the anisotropy parameter variation. Found in the case of zero-field high magnetic susceptibility χ increases with the temperature T becomes smaller, with the increase in the anisotropy parameter η, the magnetization curve to the left, in the high temperature case of an external field, η is constant, with the the temperature T increases, the magnetization m becomes large, a small low magnetic case, the anisotropy parameter η is given magnetization m increases as the temperature T becomes large as the increase in the external field h leaving mt curve upward. Our results with the results of other theoretical workers get a better match. The fourth chapter is the conclusion and future work prospects.

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