Magnetism is the force responsible for the push and pull between magnets and the attraction of metals like iron. While it may seem like a static property, the magnetism within a material is dynamic. It can be strengthened, weakened, controlled, and even removed entirely through various means.
The Source of Magnetism in Materials
The origin of magnetism in materials like iron, nickel, and cobalt lies at the atomic level with their electrons. Electrons possess an intrinsic property called spin, which gives each one a tiny magnetic moment, turning it into a microscopic magnet. In many materials, electrons exist in pairs with opposite spins, causing their magnetic effects to cancel each other out. Ferromagnetic materials, however, have atoms with unpaired electrons, resulting in a net magnetic moment for each atom.
Within these materials, quantum mechanical interactions cause the magnetic moments of adjacent atoms to align spontaneously in the same direction. This alignment occurs within localized regions known as magnetic domains. In an unmagnetized piece of iron, these domains are oriented randomly, so their magnetic fields neutralize one another, resulting in no overall magnetic effect.
Weakening and Destroying Magnetism
The organized structure of magnetic domains that creates a magnet can be disrupted, leading to a reduction or complete loss of magnetism. One effective method is through the application of heat. Exposing a magnet to high temperatures increases the thermal energy within the material, causing its atoms to vibrate more intensely. This vibration can overcome the forces holding the domains in alignment, causing them to shift into random orientations.
Every ferromagnetic material has a specific threshold known as the Curie temperature. If a material is heated beyond this point, the thermal agitation becomes so great that the alignment of the domains is completely destroyed, and the material loses its permanent magnetic properties. For instance, neodymium magnets have a Curie temperature around 310°C, while for iron, it is much higher at approximately 770°C.
Physical shock provides another way to demagnetize a material by jolting the domains out of alignment, such as by striking it with a hammer. A third method is degaussing, which exposes the magnet to a strong, alternating magnetic field. This process rapidly flips the orientation of the domains, leaving them in a random state once the external field is removed.
Creating and Strengthening Magnetism
Magnetism can be induced in an unmagnetized material by exposing a ferromagnetic object, like an iron nail, to an external magnetic field. This provides the force to align its randomly oriented magnetic domains. When the domains point in the same direction, their individual magnetic fields combine to make the object a magnet.
One technique is magnetization by induction, done by stroking the material with a strong permanent magnet. Repeatedly rubbing the magnet along the object in a single direction “combs” the domains so they all face the same way. This method creates a permanent magnet once the process is complete.
Another method uses electricity. By wrapping a coil of wire around a piece of ferromagnetic material and passing a direct current (DC) through it, a powerful magnetic field is created inside the coil. This field penetrates the material and forces its magnetic domains to align, transforming it into a magnet.
Controlling Magnetism with Electricity
The most versatile method for altering magnetism is using electricity to create an electromagnet. The basic principle is that an electric current flowing through a wire produces a magnetic field. This effect can be amplified by shaping the wire into a tight coil, known as a solenoid, which concentrates the magnetic field lines inside.
The field’s strength can be increased further by placing a piece of ferromagnetic material, or an “iron core,” inside the solenoid. This core becomes strongly magnetized by the coil’s field, and its own magnetic field adds to the coil’s, resulting in a powerful combined effect.
The primary advantage of an electromagnet is the control it offers. Its magnetic field can be turned on or off by starting or stopping the electric current. The magnet’s strength is also adjustable; increasing the current strengthens the field, while decreasing it weakens it. Reversing the current’s direction will instantly flip the magnet’s polarity.
Real-World Applications of Altered Magnetism
The ability to change magnetic properties is fundamental to many technologies, such as magnetic data storage. In a computer hard drive, a platter coated with a magnetic material stores data in tiny, distinct magnetic sectors. An electromagnetic read/write head alters the magnetic direction of these sectors to represent binary data. A credit card’s magnetic stripe functions similarly, storing information in a pattern of magnetized particles.
In heavy industry, powerful electromagnets are used in recycling facilities and scrapyards. Cranes equipped with large electromagnets can be activated to lift and move tons of scrap iron and steel. When the operator cuts the electric current, the magnetic field vanishes, instantly dropping the load.
The medical field also utilizes controlled magnetism, most notably in Magnetic Resonance Imaging (MRI). MRI machines use powerful magnets to generate a strong, stable magnetic field that temporarily aligns hydrogen atoms in the body’s water molecules. By applying and analyzing radiofrequency pulses that disrupt this alignment, the machine creates detailed images of internal structures without invasive procedures.