Néel walls
Introduction
The Néel wall, named after French physicist Louis Néel, is a concept in the field of magnetism that describes the transition between two magnetic domains in a ferromagnetic material. This transition, or "wall", is characterized by a rotation of the magnetization vector in the plane of the wall, as opposed to a Bloch Wall where the magnetization rotates out of the plane. The Néel wall is a fundamental concept in the study of ferromagnetic domains, and is particularly relevant in the field of spintronics and magnetic storage devices.
Historical Background
The concept of the Néel wall was first proposed by Louis Néel in the mid-20th century. Néel, a French physicist, made significant contributions to the field of magnetism and was awarded the Nobel Prize in Physics in 1970 for his pioneering work. The Néel wall is one of his most recognized contributions, and it has had a profound impact on the understanding of magnetic phenomena in ferromagnetic materials.
Physical Description
In a Néel wall, the magnetization vector rotates within the plane of the wall. This is in contrast to a Bloch wall, where the magnetization rotates out of the plane. The direction of rotation in a Néel wall is determined by the crystallographic structure of the ferromagnetic material and the direction of the applied magnetic field. The width of the Néel wall, like the Bloch wall, is dependent on the exchange stiffness and the anisotropy field of the material.
Mathematical Description
The mathematical description of a Néel wall involves the solution of the differential equation that describes the rotation of the magnetization vector within the wall. This equation, known as the Néel wall equation, can be derived from the Landau-Lifshitz-Gilbert equation, which is a fundamental equation in the theory of magnetism. The solution to the Néel wall equation gives the profile of the magnetization vector across the wall, and it can be used to calculate the energy of the wall and its response to an applied magnetic field.
Applications
The concept of the Néel wall is crucial in the design and operation of magnetic storage devices, such as hard disk drives and magnetic random access memory (MRAM). In these devices, information is stored in the form of magnetic domains, and the transition between these domains, which can be a Néel wall or a Bloch wall, plays a key role in the reading and writing of data. The Néel wall is also relevant in the field of spintronics, where the spin of electrons, which is related to their magnetic moment, is used to manipulate and transport information.