A successful demagnetization process requires that the current pulsating in the component diminishes monotonically and precisely. This is critical to the final result of demagnetization because even the slightest irregularities in the current pulse may interfere with the random distribution of magnetic structures in a component. Residual magnetism is a common occurrence in bulk goods, mainly on parts that have been stretched for a long time.
Demagnetization of ferromagnetic materials
The term “demagnetization” means the removal of magnetization from an object. The demagnetization process is important because magnetic material can be attracted to other metals, and this can cause problems with their magnetic field. Typical examples of demagnetized materials are tools, flatware, engine components, and molds. A small piece of steel can be demagnetized with a hammer by striking it on a non-metallic surface.
In many applications, ferromagnetic materials exhibit dipole moments that are influenced by the strength of the ambient magnetic field. These dipole moments can produce unwanted external magnetic fields. To overcome this problem, demagnetization processes are used. Typically, the process involves reducing the remanent dipole moment to a minimal level and stabilizing it. This is a crucial process for many spacecraft.
Methods of demagnetization
Various methods exist for demagnetizing objects. However, these methods are limited to isolated objects and do not work in a continuous production line. As the object has to be manually removed from the line and then demagnetized, it is inefficient and increases the risk of damage. Further, some methods do not achieve consistent results. End treatment, for example, does not solve the problem of residual magnetism and may require a large number of passes.
Another method of demagnetization involves using an open magnet circuit with a coil. A magnet core is applied to the object to be demagnetized. An alternating current is applied to the coil, and as the magnet core slowly pulls away from the object, the frequency of the supply voltage is raised to the resonance frequency of the associated oscillation circuit. The alternating field generated is weaker. It is thus desirable to use a system that provides a high degree of automation.
Effects of demagnetization on residual magnetic field
A description of the effects of demagnetization on the residual magnetic field is based on the interaction domains that form when an applied field exceeds the saturation field Ms along the preferred axis of the magnet. This initial permeability, or permeability at right angles to the applied field, can be as high as 105 in some materials. The domain wall motion often leaves nonzero components of magnetization along the preferred axis of the magnet.
A demagnetized state is a state of subdivided domains whose magnetic fields are aligned in random directions. When the field is reduced, the domain walls jump abruptly across the sample. This is a hysteretic process. The residual flux density is called the remanence, while the magnetization is known as the Br. The term coercivity refers to the strength of the reverse field needed to restore the magnetization to zero.
Limitations of the demagnetization process
One of the limitations of the demagnetization process is its inaccuracy in reproducing the original magnetism. This is due to the fact that a demagnetized metal will attract other metals when exposed to external magnetic fields. In addition, magnetic fields from other sources can cause undesired residual magnetism that may negatively affect the finished product. A demagnetizer is therefore necessary for removing undesired residual magnetism.
Another limitation of the demagnetization process is the insufficient magnetic field. A high-intensity magnetic field is required to achieve multipole magnetization on a continuous surface. It is not practical to use low-intensity magnetizers for high-volume production due to their inefficiency. In addition, high-pole-density magnets are difficult to detect with standard sensing equipment. Despite these limitations, the demagnetization process is still a valuable and necessary tool for the characterization of magnetic materials.
