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Why do magnets have such amazing memory? Explore the mystery of hysteresis!
Hysteresis occurs when the state of a system depends on its history. For example, in a given magnetic field, the magnetic moment of a magnet may have more than one value, depending on how the field has changed in the past. Often this historical dependence can be represented by a cycle or hysteresis curve, where the value of one variable changes depending on the direction of change of another variable. This memory capability is the basis for memory in hard drives and is also responsible for the retention of Earth's past magnetic field strength.
Magnetic hysteresis is not limited to ferrites and dielectric materials; it also occurs in many natural phenomena such as the deformation of rubber bands and shape memory alloys.
Magnetic hysteresis can be observed in various fields including physics, chemistry, engineering, biology and economics. Hysteresis is also found in many artificial systems, such as thermostats and Schmitt triggers, where it prevents unnecessary frequent switching. The existence of hysteresis allows a dynamic delay to exist between input and output in a given system, which is called rate-dependent hysteresis. However, phenomena like magnetic hysteresis loops are primarily rate-independent, which makes persistent memory possible.
In hysteresis models such as the buckled axis model and the Bou-Wen model, the overall characteristics of hysteresis can be captured, while some empirical models target specific phenomena, such as the Jiles-Atherton model for ferromagnetism.
The term hysteresis comes from the Greek word "ὑστέρησις", which literally means "deficiency" or "delay". The term was first coined by James Alfred Ewing in 1881 to describe the behavior of magnetic materials. Over time, many researchers have studied the description of hysteresis in mechanical systems, especially in the early work of James Clerk Maxwell. The subsequent study of the hysteresis model also attracted the attention of famous scientists such as Ferenc Prysach, Louis Neel and Douglas Hugh Everett, who studied the hysteresis related to magnetism and adsorption. Dig deeper.
Types of Hysteresis
Hysteresis can be divided into two categories: rate-dependent and rate-independent. Rate-dependent hysteresis reflects the lag relationship between input and output. For example, a sine wave input X(t) produces a phase-delayed sine wave output Y(t).
Rate-independent hysteresis, on the other hand, means that the system's memory of its past states does not decay over time. This means that if a variable X(t) changes cyclically, the output Y(t) may show a different value when it returns to its initial state, depending on the process path of X(t) rather than the rate of change.
Many authors restrict the term hysteresis to rate-independent hysteresis.
Application Areas
In control systems, hysteresis can be used to filter signals so that the system's output response is not too drastic. For example, a thermostat turns on a heater when the temperature drops to a certain level, but does not turn it off until the temperature rises to another threshold; in circuits, hysteresis is intentionally added to circuits to prevent unnecessarily rapid switching. This technique can be used to compensate for the fluctuation of switching contacts and can also be applied to the processing of noisy signals.
In user interface design, hysteresis helps to make the state of the interface lag behind the user's input. Even after the user's input changes, the interface will remain in its current state for a period of time, making it more user-friendly. Smooth.
Application of Hysteresis in Materials
For example, in ferromagnetic materials, when an external magnetic field is applied, the atomic fields align with it, and even when the external field is removed, some of the alignment remains, which is one of the reasons why hard drives are based on magnetic memory. . To demagnetize the material, heat or a reverse magnetic field is required.
This unique memory phenomenon exists not only in hard drive design, but is also widely used in other storage media and electronic components, demonstrating the diversity of hysteresis and its importance in modern technology.
This in-depth look at the phenomenon of hysteresis raises the question of how future memory devices might exploit these natural phenomena to create more efficient forms of memory as technology advances.
