What is the principle of hysteresis, and how does it apply to magnetic materials?
The principle of hysteresis is a fundamental concept in physics, engineering, and materials science. Although it has various applications, one of the most common areas where it’s encountered is in magnetic materials. In this context, it describes the lagging of magnetic effects in a material when subjected to changing magnetic fields.
Hysteresis and Magnetic Materials
To begin with, let’s define hysteresis. The term “hysteresis” originates from a Greek word that means “to lag behind”. In physics, it generally refers to a system’s property whereby the system doesn’t instantly follow the force applied to it and is instead dependent on its past states.
When it comes to magnetic materials, hysteresis is typically observed when a magnetic field is applied to a ferromagnetic material like iron, nickel, or cobalt. When you increase the magnetic field, the magnetization (which is the measure of a material’s magnetic moment per unit volume) of the material also increases. However, when you decrease the magnetic field, the magnetization doesn’t immediately return to its original state. Instead, it lags behind, and this is the property we call magnetic hysteresis.
Magnetic Hysteresis Loop
A typical way to represent magnetic hysteresis is with a hysteresis loop (or B-H curve). On a graph where the x-axis is the applied magnetic field (H) and the y-axis is the magnetization (B), as you increase the magnetic field from zero, the magnetization also increases, following a certain curve. When you decrease the magnetic field back to zero, instead of retracing the same curve, the magnetization follows a different path.
When the magnetic field is reversed, the magnetization decreases to zero, goes into the negative, and follows yet another curve. When the magnetic field is returned to its original value, the magnetization doesn’t immediately go back to the original state. Instead, it takes a certain amount of field strength to bring it back, completing the loop.
The area inside this hysteresis loop represents the energy dissipated as heat in a magnetic material due to the changing magnetic fields. This is an important property when it comes to applications like transformers, where minimizing this energy loss is crucial for efficiency.
Understanding Hysteresis Through Domains
The underlying cause of hysteresis lies in the microscopic structure of ferromagnetic materials. These materials consist of tiny regions known as domains. Each domain is like a tiny magnet, with all the atomic magnets aligned in one direction.
When an external magnetic field is applied, these domains change their size and orientation. Domains aligned with the field grow, while others shrink. This reorientation doesn’t happen instantly and depends on the material’s previous state. When the field is removed or reversed, the domains don’t immediately return to their original arrangement, hence leading to the observed hysteresis behavior.
Applications
Understanding magnetic hysteresis is vital for various applications. In power transformers, hysteresis loss leads to wasted energy, so materials with low hysteresis are desired. In magnetic storage devices like hard drives, hysteresis is beneficial as it means that the stored information (in the form of magnetization) remains stable against small disturbances. In magnetic sensors and other components, the hysteresis characteristics can influence the device’s behavior and performance.
In summary, the principle of hysteresis is a cornerstone in understanding and manipulating magnetic materials, making it a key concept in modern electronics and materials science.
