Charging a magnet refers to imparting magnetic properties to a non-magnetic material or restoring the strength of a weakened magnet. This process, distinct from electrical charging, focuses on organizing a material’s internal structure to exhibit magnetic force. The aim is to align microscopic magnetic regions within a material, allowing it to attract or repel other magnetic substances.
The Science of Magnetization
Materials become magnetized due to their atomic structure, specifically microscopic regions called magnetic domains. In each of these domains, the magnetic fields of individual atoms are aligned in a uniform direction.
In an unmagnetized material, these magnetic domains are typically oriented randomly, with their magnetic effects canceling each other out. This random arrangement results in no overall magnetic field being observable. Magnetizing a material involves aligning these otherwise disordered magnetic domains.
Only specific substances, known as ferromagnetic materials, can be magnetized in this way. Common examples include iron, nickel, cobalt, and their various alloys. When these materials are exposed to an external magnetic field, their domains begin to rotate and align with that field. If the external field is strong enough, or the material is treated appropriately, this alignment can become permanent, turning the material into a magnet.
Practical Magnetization Methods
Stroking Method
One common approach to magnetizing a material is the stroking method, which utilizes an existing magnet. To perform this, one pole of a strong magnet is rubbed along the length of a ferromagnetic material, such as a steel bar, in a single, consistent direction. After each stroke, the magnet must be lifted clear of the material before beginning the next stroke from the starting point. This repeated, unidirectional motion helps to align the magnetic domains within the material, gradually imparting magnetism.
Induction Method
Another technique is the induction method, where a ferromagnetic material is magnetized without direct physical contact. This occurs when the material is simply brought into close proximity with a strong magnet. The magnetic field of the permanent magnet induces an opposing pole in the nearest end of the material, causing its internal domains to align. While often temporary, maintaining this close contact for an extended period or using a very powerful inducing magnet can result in a more lasting magnetization.
Electromagnetism
Electromagnetism offers a controlled and often more powerful method for magnetizing materials. This involves coiling insulated wire tightly around a ferromagnetic core, such as an iron nail. When an electric current is passed through the wire coil, it generates a magnetic field around the core, temporarily turning it into a magnet. The strength of this temporary magnet can be adjusted by changing the current or the number of wire turns.
Demagnetization and Recharging
Magnets can become demagnetized due to several factors. Exposure to high temperatures can cause the magnetic domains within a material to become disordered and misaligned. Physical shocks, such as dropping or striking a magnet, can also disrupt this alignment and reduce its strength. Over time, and even with proper care, magnets can experience a gradual reduction in their magnetic properties.
Strong opposing magnetic fields or exposure to alternating electric currents can also lead to demagnetization. Corrosion or physical damage to the magnet’s structure can further contribute to a loss of magnetic performance. Proper storage is therefore important to help maintain a magnet’s strength and longevity.
To prevent demagnetization, magnets should be stored in a cool, dry place, away from heat sources and strong electrical currents. Using a magnet keeper, which is a piece of iron placed across the poles, can help maintain the magnetic field and prevent weakening. Storing magnets in pairs with their unlike poles aligned can also be beneficial. If a magnet has weakened, the same methods used for initial magnetization, such as stroking with a stronger magnet or exposure to an electromagnetic field, can often be employed to recharge it.