A Brief Note on Properties of Magnetism

Permanent magnets are objects manufactured from materials that have been magnetized and have the ability to generate their own persistent magnetic field. A common example is a refrigerator magnet, which is used to hold notes on the inside of a refrigerator door. Ferromagnetic materials are those that can be magnetized and are also those that are highly attracted to a magnet; these are the materials that can be magnetized (or ferrimagnetic). These include the elements iron, nickel, and cobalt, as well as their alloys, some rare-earth metal alloys, and some naturally occurring minerals, such as lodestone, among other elements and compounds. Despite the fact that ferromagnetic (and ferrimagnetic) materials are the only ones that are significantly attracted to a magnet and are therefore considered magnetic, all other substances respond weakly to a magnetic field, responding through one of several different types of magnetism.

Ferromagnetic materials can be divided into two categories: magnetically “soft” materials such as annealed iron, which can be magnetized but do not tend to remain magnetized, and magnetically “hard” materials, which do tend to remain magnetized. During the manufacturing process, permanent magnets are made from “hard” ferromagnetic materials such as alnico and ferrite, which are subjected to special processing in a strong magnetic field to align their internal microcrystalline structure, resulting in a magnet that is extremely difficult to demagnetize. To demagnetize a saturated magnet, a specific magnetic field must be provided, and the threshold at which this occurs is determined by the coercivity of the material under consideration. Coercivity is a property of “hard” materials, whereas coercivity is a property of “soft” materials. When it comes to magnets, their overall strength is assessed by their magnetic moment, or alternately, by the entire magnetic flux they produce. The magnetization of a material is used to determine the local strength of magnetism in that material.

An electromagnet is a coil of wire that behaves as a magnet when an electric current travels through it, but that ceases to function as a magnet when the current is interrupted or terminated. Most of the time, the coil is wrapped around a core made of “soft” ferromagnetic material, such as mild steel, which considerably increases the magnetic field created by the coil as a result of the wrapping.

Usages That Are Common

• Magnetic recording media: VHS tapes are made up of a reel of magnetic recording media. The information that makes up the video and sound on the tape is encoded on the magnetic coating that protects the tape from being damaged. Magnetic tape is also used in the production of common audio cassettes. In a similar vein, floppy disks and hard discs in computers store data on a thin magnetic coating to which data is written. All of these cards have a magnetic strip on one side, including credit, debit, and automatic teller machine cards.  Identification cards: This strip encodes the information necessary to contact a person’s financial institution and establish a connection with their account information (s). 
• Vintage televisions (those that are not flat screens) and older huge computer displays include: A cathode ray tube, which is used in television and computer screens, is guided to the screen by an electromagnet, which is controlled by a computer. 
• Speakers and microphones are available: In order to transform electric energy (the signal) into mechanical energy, most speakers use a permanent magnet and a current-carrying coil (movement that creates the sound). The coil is wound around a bobbin that is attached to the speaker cone, and it transmits the signal as a changing current that interacts with the field of the permanent magnet in the speaker. The voice coil detects a magnetic field and, in response, moves the cone and pressurises the surrounding air, resulting in the production of audio sound. Dynamic microphones work on the same principle as static microphones, but in the opposite direction. A microphone is made up of a diaphragm or membrane that is linked to a coil of wire by a spring. The coil is held in place by a magnet that has been properly designed. When sound causes the membrane to vibrate, the coil is also vibrated in response. Induced voltage is created across the coil as the coil travels through the magnetic field of the magnet. This voltage causes a current to flow across the wire, which is a characteristic of the original audio signal.
• Electric guitars make use of magnetic pickups to convert the vibration of the guitar strings into electric current, which can then be amplified via amplification. This differs from the concept that underpins the speaker and dynamic microphone in that the vibrations are detected directly by the magnet, rather than through a diaphragm. The Hammond organ, which used revolving tonewheels instead of strings, operated on a similar basis.

Ferromagnets That Are Demagnetizing

Demagnetization (or degaussing) of magnetized ferromagnetic materials can be accomplished in a variety of methods.

• When a magnet is heated over its Curie temperature, the molecular motion causes the alignment of the magnetic domains to be disrupted. This always completely eliminates all magnetization.
• This is accomplished by placing the magnet in an alternating magnetic field with intensity that is greater than the material’s coercivity, and then either removing the magnet out or gradually decreasing the magnetic field until it is no longer there. In commercial demagnetizers, this is the principle that is used to demagnetize tools, erase credit cards, and hard discs, as well as in degaussing coils that are used to demagnetize CRTs.
• In the event that any section of the magnet is subjected to a reverse field greater than the magnetic material’s coercivity, some degree of demagnetization or reverse magnetization will occur.
• The demagnetization of a magnet occurs gradually if the magnet is subjected to cyclic fields strong enough to pull the magnet away from the linear component of the B–H curve of the magnetic material in the second quadrant of the magnetic material (the demagnetization curve).
• A mechanical disturbance, such as hammering or jarring, has the potential to randomise magnetic domains and diminish magnetization of an object, but it may also inflict unacceptable damage.

Where Is the Magnetic Field the Most Powerful

Because each individual piece of iron is a small dipole, iron filings form a pattern that traces field lines when arranged in a grid (the separation between magnetic fields). In a dipole, the force experienced by the dipole is proportional to its strength and proportional to the rate at which the magnetic field changes. The dipole tries to align itself with a magnetic field, but the field lines at the ends of a bar magnet are quite close together, making this difficult. What this demonstrates is that the magnetic field changes strongly over a short distance, as opposed to the variation closer to the magnet’s center of gravity. Because of the drastic variations in the magnetic field, a dipole experiences greater force than a point magnet.

The strength of the magnetic field changes according to where it is located in relation to the magnet. Any pole of a bar magnet has the greatest magnetic field strength, and this is true for either pole of the magnet. When comparing the strength of the magnetic field at the north pole and the south pole, it is equal. The magnetic force is weakest in the center of the magnet and halfway between the pole and the center of the magnet, as shown in the diagram.

Conclusion 

Permanent magnets are items made of magnetized materials that can generate their own magnetic field. A refrigerator magnet, for example, is used to keep notes on the inside of a refrigerator door. Ferromagnetic materials are those that can be magnetized and are greatly attracted to a magnet (or ferrimagnetic). These include iron, nickel, and cobalt, as well as their alloys, rare-earth metal alloys, and naturally occurring minerals like lodestone. All other substances respond weakly to a magnetic field, responding through one of several forms of magnetism.