Magnetism or magnetic is a force of physics that brings about the attraction or warding off of objects. It is achieved as a consequence of the movement of electrons.
History of Magnetism
Although magnetism was widely incorporated into numerous technologies at the start of the 20th century, it has a vast and rich history. The origin of magnetism can be traced back to as early as 600 B.C. and it is believed to have been discovered by ancient Greeks.
Magnetism was first detected in lodestone, which is a form of mineral capable of attracting ferromagnetic materials. This mineral was made of iron oxide.
From 1540-1603, William Gilbert studied magnetism using scientific methodologies and this saw him conclude that even the earth exhibits magnetic forces. In the 18th century, Charles Coulomb discovered the inverse square law of force.
He concluded that the force of attraction shared by two magnetic materials is commensurate to the result of their individual fields. He further established that this attractive force is inversely proportional to the square of the stretch between them.
In 1831, Michael Faraday established electromagnetic induction and this became the foundation stone for the development of magnets for generators.
As we approached 1931, Alnico magnets were invented and by 1966, SmCo magnets were developed by scientists. These inventions have seen magnets become irrefutable components in various appliances and applications.
Understanding the Laws of Magnetism
The primary law of magnetism is centered on the principle of dissimilar poles attracting and similar poles repelling. This law is proven when like poles (e.g. north and north) from adjacent magnets are brought close together. Repulsion is detected. However, if opposite poles are brought close together, they attract.
There is also the law of magnetic fields which is centered on the magnetic fields created by magnets. These fields often cover spaces close to the magnet, where magnetic forces are exhibited. As the distance between the magnet and the object grows, the magnetic field strength shrinks.
Properties of Magnetism
Magnetism is a natural phenomenon that has been extensively studied and applied over the years. Magnetic materials exhibit various magnetic properties and here is a breakdown of the key magnetism properties.
· Magnetic Force
Magnetic force is a key magnetism characteristic that explains the nature of behavior exhibited when objects come within range of a magnet. The nature of this behavior can either be:
- Attraction: This behavior applies to objects or materials with magnetic capabilities. Ferromagnetic objects get drawn close to the magnet when brought within the range of the magnetic field. For instance, if you bring closer iron nails to a bar magnet, the nails will be attracted by the magnet and they will cling onto it.
- Repulsion: Repulsion is a behavior exhibited when objects lacking magnetic properties are placed within a magnetic field. This is also exhibited when similar poles are placed close together. The poles are thrust back.
- Directive Property: This property looks at the direction in which magnets point when freely dangled. When you strap a rope in the middle of a bar magnet and hang it to ensure it moves freely, you will notice that the magnet will take up a north-south direction.
· Magnetic Poles
Magnetism is based on opposite poles and this is demonstrated by the north and south magnetic poles found in all magnets. These poles are responsible for the attraction and/or repulsion properties of magnets. Dividing a bar magnet into two results in the creation of another magnet equipped with a north pole as well as a south pole.
· Magnetic Fields
Magnetic fields represent a region in which the magnetic forces of a magnet are active or effective. Magnetic materials can generate their own magnetic fields as is shown by permanent magnets or they can rely on external fields as is shown by electromagnets. Ideally, magnetic field lines originate at the north pole and head towards the south pole.
· Magnetic Domains
Magnetic materials contain atoms that align uniformly in specific areas to create magnetic moments. These moments then combine and align evenly and systematically to create magnetic domains. This alignment results in the generation of robust magnetic fields. However, reversing the alignment of the magnetic domains can result in the loss of magnetic properties.
Magnetic Fields and their Characteristics
Magnetic fields are areas often close to magnets, where magnetic forces are exhibited. This region sees the magnetic capabilities of magnets come to life and the forces react to the motion of electrons. Magnetic field lines cannot be seen by the naked eye but they can be visualized thanks to certain simple techniques.
All magnets including bar magnets and horseshoe magnets have north and south magnetic poles. However, the curvature in horseshoe magnets means that the poles lie along the same line.
The magnetic fields, however, flow from the north pole and reenter the magnet at the south pole just like in bar magnets. This means that the magnetic field in a horseshoe magnet is strongest in between the poles.
Characteristics of Magnetic Fields
- Magnetic field lines typically emanate from the north magnetic pole and they re-enter at the south magnetic pole.
- Magnetic field lines hardly crisscross one another.
- The strength of a magnetic field can be gauged or measured in teslas (T).
- As the distance grows, the magnetic field strength shrinks.
- Magnetic field lines exhibit similar strength.
- The magnetic field strength can be reduced by shielding using materials like Mu-metal.
Types of Magnetic Materials
Magnetic material simply refers to matter used to create magnets. This matter must demonstrate strong magnetic properties.
Today, there are multiple magnetic materials exploited to manufacture magnets. The difference is exhibited in the features and properties of the material. Here are the primary types of magnetic material at present:
· Ferromagnetic Material
A ferromagnetic material is undoubtedly the most prominent type of magnetic material. The material is extensively used because it demonstrates strong magnetic forces and its ability to retain magnetic field strength even where there is no external magnetic field.
Ferromagnetic materials are primarily used to manufacture permanent magnets and they are essentially made from substances like iron, cobalt, and nickel.
Ferromagnetic Material Features
- High Magnetic Inclination: Ferromagnetic materials are often characterized by a high likelihood of gaining magnetic properties when subjected to stronger magnetic fields.
- Magnetic Domain: In ferromagnetic matter, there are atoms aligned in a similar direction and this leads to the formation of magnetic moment. The moments are then enjoined and aligned to form magnetic domains.
- Magnetic Hysteresis: When ferromagnetic materials are withdrawn from the presence of external magnetic fields, they still retain magnetic capabilities. The hysteresis effect in ferromagnetic materials is experienced when a lag is witnessed after the removal of external magnetic fields.
· Paramagnetic Material
Paramagnetic materials are essentially the opposite of ferromagnetic materials. When subjected to external magnetic fields, they experience weak magnetization.
Additionally, they do lose their magnetic properties when the external magnetic field I withdrawn. Examples of paramagnetic materials include platinum and aluminum.
Paramagnetic Material Features
- Low Magnetic Inclination: Compared to ferromagnetic materials, their ability to become magnetized is relatively low. Their magnetization is also temporary and can be lost when the external magnetic field is withdrawn.
- Curie Temperature: Paramagnetic materials tend to suffer the loss of magnetism when they are exposed to high temperatures. Their magnetic susceptibility also decreases as temperature rises.
- Applications: Paramagnetic materials have low magnetic susceptibility and this disqualifies their application in the making of permanent magnets. They are however ideal for MRI machines, scientific research, and magnetic separation.
· Diamagnetic Materials
Diamagnetic materials are simply materials with no magnetic properties (Non-magnetic materials). They include wood, plastics, water, and certain metals. When diamagnetic matter is subjected to a magnetic field, the moments in them are created inversely in relation to the magnetic field. This results in repulsion.
Diamagnetic Material Features
- Negative Magnetic Inclination: Whenever diamagnetic materials are exposed to external magnetic fields they are thrust off or repelled. This is because they have negative magnetic susceptibility.
- Weak Response: When diamagnetic materials are placed close to ferromagnetic materials or even paramagnetic materials, they are overshadowed. They have a low magnetic response.
· Ferrimagnetic Materials
Ferrimagnetic materials share certain properties with ferromagnetic materials, for instance, permanent magnetism. They are however differentiated by the two sublattices that are antiparallel and demonstrate magnetic moments with unequal magnitudes. A good example of a ferromagnetic material is a magnetite (Fe3O4).
Ferrimagnetic Material Features
- Net Magnetization: Ferrimagnetic materials are characterized mainly by a net magnetic moment. This is caused by the unbalanced alignment of magnetic moments in their sublattices.
- Remanence: Ferrimagnetic materials also keep hold of magnetism even in the absence of external magnetic fields.
· Antiferromagnetic Materials
In antiferromagnetic materials, the atoms which align to create magnetic moments tend to line up in opposing directions. This sees them nullify one another resulting in zero net magnetization. The most prominent antiferromagnetic material is manganese oxide.
Antiferromagnetic Material Features
- Zero Net Magnetization: The magnetic moments in antiferromagnetic materials cancel each other out and this results in zero net magnetization.
- Neel Temperature: When antiferromagnetic materials are subjected to heat beyond a specific temperature point, the order of the atomic magnetic moments is deranged. This point is known as Neel temperature and surpassing this point can cause the antiferromagnetic material to exhibit paramagnetic behavior. For manganese oxide materials, the Neel temperature tends to be −151° C.
How to Measure Magnetism?
Magnetism is a very intriguing and indispensable phenomenon hence it is broadly used in today’s world.
There are multiple techniques, parameters, and tools that can be exploited to measure magnetism, and here is a brief overview of the most effective ways to measure magnetism.
· Magnetic Field Strength Measurement
Measuring the strength of the magnetic field generated by a magnetic material is one way to gauge its magnetic strength.
Computing the intensity of a magnetic field can be accomplished using a Hall effect sensor or a magnetometer. The unit for measuring magnetic field strength is typically amperes per meter (A/M). Alternatively, oersteds (Oe) can be used.
· Magnetic Flux Density
Magnetic flux density is generally computed using flux meters and it is often weighed in teslas (T) or gauss (G).
This measurement attempts to establish the power of a magnetic field at a precise point. The magnetic flux density is typically symbolized by the letter (B).
· Permeability
Permeability is often expressed in (μ) and it is measured in henrys per meter (H/m). It gauges the magnetization capability of magnetic matter. Measuring permeability gives one a glimpse of how well a magnetic material can conduct magnetic flux.
· Magnetic Susceptibility Measurement
Magnetic susceptibility looks at the likeliness of a magnetic material to gain magnetic powers when subjected to external magnetic fields. Different magnetic materials exhibit distinct magnetic susceptibility. This parameter can be gauged using magnetic susceptibility meters or balances.
Instruments for Measuring Magnetism
At present, there are a myriad of instruments that can be utilized to establish various aspects of magnetism. The ability to measure these aspects helps us quantify the power of magnetism as well as optimize the power of magnets.
· Hall Effect Sensor
Hall effect sensors are some of the most heavily utilized tools when it comes to measuring magnetism. They are primarily used to gauge the strength of a magnet’s magnetic field. They are semiconductor instruments that generate a voltage equivalent to the measured magnetic field.
· Compass
Compasses have long been utilized to detect magnetism. They constitute magnetic needles that line up with the magnetic fields emitted by the earth. A compass helps determine the direction of magnetic field lines.
· Gauss Meter
A Gauss meter is uniquely designed to weigh the strength of magnetic fields. It measures field strength in gauss (G). They can be immobile or handheld and they are often utilized by engineers and scientists.
· SQUID Magnetometer
Squid magnetometers are known for being highly efficient and sensitive. This makes them ideal for measuring magnetic fields even when they are extremely inferior. These meters often necessitate cryogenic temperature to operate optimally.
What Causes Magnetism?
Magnetism is a concept that has been fascinating to scientists and scholars for years. However, as the years came by more advanced concepts have been advanced and used to help better our understanding of magnetism. Here is a brief look at some of the theories that have been used to decipher magnetism.
· Magnetism and the Domain Theory
The domain theory was developed in the 20th century and it seeks to explain magnetism by looking at the atomic or molecular arrangement of magnetic materials.
This theory argues that magnetic materials comprise atoms, which align in similar directions to create magnetic domains. The domains are created once multiple atoms line up uniformly to create magnetic moments.
Before a magnetic material is magnetized, the arrangement of the atoms in magnetic domains is random. However, once the material is magnetized or exposed to an external magnetic field, the domains line up uniformly.
Although this theory explains how magnetism works in certain magnetic materials, it does not explain other aspects of magnetism. And this is where the atomic theory comes in.
· Magnetism and the Atomic Theory
The atomic theory is founded on the invention made in the 19th century that saw scientists utilize magnetism to create electricity while also using electricity to create magnetism.
However, the atomic theory was utilized to elucidate magnetism in the 20th century. This theory proposes that magnetic materials are made of atoms and these atoms consist of electrons, protons, and neutrons.
The electrons are located at the periphery of the nucleus and they are constantly on the move around the orbit. They also experience a phenomenon known as electron spin, which results in magnetic moments.
Besides, the magnetic moment created depends on the level of the electron spin. These moments interact with other moments to create magnetic domains and this results in stronger magnetic fields.
How Magnets Work?
Despite being widely used in essential devices and applications like loudspeakers and medical equipment, many people do not understand how they work. Underneath, we explore the basics of magnetism so as to explain how magnets work.
· Atomic and Subatomic Configuration
Magnetic materials just like all matter have atoms at their core. These atoms are then endowed with electrons, neutrons, and protons. The electrons surround the atom’s nucleus and by constantly orbiting the nucleus, they bring about electron spin.
· Electron Spin
Electrons are subatomic particles whirling around the atom’s nucleus. They are negatively charged and have a spinning capability, which simply creates a magnetic field around the electrons. In magnetic materials, the spins are uniformly oriented and this results in the creation of a robust net magnetic field.
· Magnetic Moment
The uniform alignment of the electron spins creates magnetic moments. These moments are generated once a magnetic material like iron is subjected to superior external fields.
Furthermore, the consequential alignment of the magnetic moments leads to the creation of magnetic domains.
· Magnetic Domains
Magnetic domains are ideally miniature magnets within a magnet and they are a consequence of multiple magnetic moments lining up in a uniform direction.
In non-magnetic materials, the domains are randomly oriented but in magnetized materials, they are uniformly aligned. Domains are typically created once a superior magnetic field is introduced leading to the magnet’s north pole lining up with the external magnetic field.
· Attraction and Repulsion
With the magnetic moments and domains fully and uniformly aligned, one has a fully functional magnet. The magnet can now interact with distinct objects and this interaction takes up two forms; attraction or repulsion.
Attraction is initiated towards objects with magnetic capabilities like metals. Ideally, dissimilar poles attract whereas poles that are alike repel.
Types of Magnets
Today, you can come across varying types of magnets characterized by different properties, magnetic strengths, and even shapes. However, there are two primary types of magnets:
· Permanent Magnets
Permanent magnets are characterized by the longevity in which they hold onto magnetism. They are easily magnetized, exhibit strong magnetic fields, and retain magnetic properties perpetually. They are further categorized into:
- Alnico Magnets: Alnico magnets are named after the compounds they are made from i.e. aluminum, nickel, and cobalt. They exhibit great magnetic field strength and can withstand extreme temperatures.
- Neodymium Magnets: These magnets are characterized by the compounds they are manufactured from i.e. neodymium, iron, and boron. They are quite prominent because they are extremely strong.
- SmCo Magnets: SmCo magnets are magnets manufactured from samarium and cobalt. They are revered for being corrosion-resistant and their magnetic prowess is evidenced by their exceptional high-temperature resistance.
- Ceramic Magnets: Also referred to as ferrite magnets, ceramic magnets are relatively pocket-friendly and they have high coercivity. They are manufactured from iron oxide and are mainly used as refrigerator magnets.
- Bar Magnets: Bar magnets bear the look of a triangle hence why they are named bar magnets. They can be recognized by their long and narrow look. They are extensively used in motors, medical equipment as well and compasses.
- Horseshoe Magnets: Horseshoe magnets bear the shape of the letter ‘U’. This means that the north and south poles lie at the tip of the U-shape and this makes their magnetic fields strongest at the tips.
- Ring Magnets: Characterized by an annular shape similar to that of a ring, ring magnets have their magnetic fields concentrated on the inside of the ring’s hole. They are ideal for research, magnetic separation, and audio speakers.
· Temporary Magnets
Temporary magnets are magnetic objects that gain and lose magnetism under specific conditions. For instance, they gain magnetic powers when an external magnetic field is introduced and they lose these powers once the field is eliminated. They can be manufactured using varying materials including paramagnetic and diamagnetic materials. Temporary magnets are ideal for applications that require magnetic forces momentarily.
· Electromagnets
Electromagnets are unique types of magnets that utilize electricity to induce magnetism. They rely on magnetic fields created using electric currents. Their composition includes a magnetic material wrapped with a coil of wire. Whenever a current is passed around the wire, a magnetic field is generated. Once it is turned off, the magnetic field is lost and the magnet loses its magnetic properties.
Magnetic Induction
Magnetic induction is at times referred to as electromagnetic induction and it is a process that chronicles how electromotive force (EMF) is created in a conductor once subjected to a dynamic magnetic field. This concept is witnessed in the majority of today’s electrical devices including generators and inductors. It is initiated when the magnetic field is manipulated leading to an increase or decrease in the field strength close to a conductor.
Faraday’s Law of Electromagnetic Induction
Michael Faraday is a renowned English scientist fondly remembered for formulating Faraday’s law of electromagnetic induction in the 19th century.
This law attempts to explain how the dynamics of a changing magnetic field impact voltage in a closed circuit. It is however broken down into two parts and here is an explanation of both laws.
The First Law of Electromagnetic Induction
In the first law, Faraday argues that setting up a conductor in a changing magnetic field will result in the induction of electromotive force. Breaking off the circuit on the conductor then results in the origination of an induced current.
The intensity of the magnetic field can be manipulated by adjusting the distance between the magnet and the coil. Of course, this is alongside by pulling the coil towards or away from the magnetic strength. Here is the respective formula:
Ε = -dΦ/dt
- Ε denotes the induced electromotive force (emf) in volts (V).
- dΦ/dt denotes the rate of change of magnetic flux (Φ) through the loop with respect to time (t).
The Second Law of Electromagnetic Induction
In the second law, Faraday argues that the induced electromotive force realized in the coil is proportional to the flux linkage change rate. Flux linkage refers to the total the sum of turns in the coil as well as the coil flux. Here is the respective formula:
Δn = Q / (zF)
- Δn symbolizes the moles of substance produced during the electrolysis.
- Q symbolizes the electric charge passed through the electrolyte in coulombs (C).
- z symbolizes the number of moles of electrons required to produce or consume one mole of the substance during the electrolysis.
- F is the Faraday constant, approximately 96,485 C/mol.
Practical Applications of Magnetism
Magnetism is a prominent technology and it finds extensive usage in multiple applications transcending varying aspects of everyday life. Underneath are some of the most pivotal uses of magnetism today.
· MRI Machines
Magnetism is a concept that has proven to be indispensable in medical diagnostics particularly when it comes to magnetic resonance imaging (MRI). With specially designed magnets, doctors can visualize internal organs easily resulting in better and more precise diagnostics.
· Credit Card Strips
Magnetism is also utilized in credit card strips as well as other smart cards to reserve essential information. In many financial cards, the magnetic strip is in form of a black stripe that can be scanned easily by bank scanners or ATM machines.
· Magnetic Levitation
In magnetic levitation or transportation, magnetism is employed to levitate vehicles or trains. This necessitates high-power magnets capable of upholding and thrusting heavy objects such as trains. The use of Maglev has greatly eased the process of transportation.
· Magnetic Storage
Magnetism has also proven to be a very highly beneficial technology when it comes to storage. Hard drives now utilize magnetic stripes to preserve data and the reading ports utilize magnetic fields to read the preserved data.
· Magnetic Separation
Magnetic separation is one of the key applications of magnetism. Highly robust magnets are deployed to alienate distinct objects from others based on their magnetic affinity. For instance, magnetism is widely utilized in mining industries to separate precious metals from other objects.
Conclusion
As you can see, magnetism plays an important role in modern industrial and domestic applications. There are different types of magnets for unique application requirements.
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