Electromagnetic hysteresis is a phenomenon that occurs in ferromagnetic materials when they are subjected to alternating magnetic fields. It refers to the lagging of the magnetization of a material behind the changes in the magnetic field that's applied to it. This lag creates a loop-shaped pattern when the magnetization is plotted against the magnetic field strength, and this loop is called the hysteresis loop.
Here's a breakdown of the concept:
Ferromagnetic Materials: Ferromagnetic materials, such as iron, nickel, and cobalt, have the property of exhibiting strong magnetization when subjected to an external magnetic field. This magnetization is due to the alignment of their atomic magnetic moments in response to the applied field.
Magnetic Domains: Inside a ferromagnetic material, there are regions known as magnetic domains. Each domain consists of a large number of atomic magnetic moments that are aligned in a particular direction. These domains can be randomly oriented in the absence of an external magnetic field.
Alignment of Magnetic Moments: When an external magnetic field is applied to a ferromagnetic material, the magnetic moments within the domains tend to align with the direction of the field. As the field strength increases, more and more domains align, leading to an increase in the material's overall magnetization.
Saturation: At a certain point, all the magnetic domains become fully aligned with the applied field, and the material reaches a state of magnetic saturation. This is when the material's magnetization cannot increase further, even if the applied field becomes stronger.
Changing the Magnetic Field: If the external magnetic field strength is reduced (or reversed), the magnetic domains don't immediately revert to their original random orientations. Instead, they tend to stay partially aligned due to the influence of neighboring domains. This causes the material's magnetization to remain higher than it would be if it were truly demagnetized.
Hysteresis Loop: As the external magnetic field strength is varied over a full cycle, the material's magnetization follows a loop-shaped pattern. This loop is called the hysteresis loop. The loop's shape is due to the fact that the magnetization lags behind the changes in the magnetic field. The width of the loop indicates the energy lost as heat during each cycle, which is a result of the material's internal friction as the domains realign.
Reversal of Magnetization: To completely reverse the magnetization, the applied magnetic field needs to exceed a certain threshold known as the coercive force. This force is required to break down the alignment of domains and set them in the opposite direction.
Electromagnetic hysteresis has practical implications in various industries. For example, in transformer cores and magnetic memory devices, understanding hysteresis is crucial to ensuring efficient and reliable performance. It's also relevant in areas like materials science and engineering, where precise control over magnetic properties is important for designing electronic devices and systems.