There are two main types of magnets: permanent and electromagnets. You can determine what a permanent magnet is based on its main properties. A permanent magnet gets its name because its magnetism is always “on.” It generates its own magnetic field, unlike an electromagnet, which is made of wire wrapped around an iron core and requires current to flow to create magnetic field.
History of the study of magnetic properties
Centuries ago, people discovered that some types rocks have original features: attracted to iron objects. Mention of magnetite is found in ancient historical chronicles: more than two thousand years ago in European and much earlier in East Asian. At first it was regarded as a curious object.
Later, magnetite was used for navigation, finding that it tends to occupy a certain position when given the freedom to rotate. Scientific research carried out by P. Peregrine in the 13th century, showed that steel could acquire these characteristics after being rubbed with magnetite.
Magnetized objects had two poles: “north” and “south,” relative to the Earth’s magnetic field. As Peregrine discovered, isolating one of the poles was not possible by cutting a fragment of magnetite in two - each individual fragment ended up with its own pair of poles.
In accordance with today's concepts, the magnetic field of permanent magnets is the resulting orientation of electrons in a single direction. Only some types of materials interact with magnetic fields; a much smaller number of them are capable of maintaining a constant magnetic field.
Properties of permanent magnets
The main properties of permanent magnets and the field they create are:
- the existence of two poles;
- opposite poles attract, and like poles repel (like positive and negative charges);
- magnetic force imperceptibly spreads in space and passes through objects (paper, wood);
- An increase in MF intensity is observed near the poles.
Permanent magnets support MPs without external assistance. Depending on their magnetic properties, materials are divided into main types:
- ferromagnets – easily magnetized;
- paramagnetic materials – are magnetized with great difficulty;
- Diamagnets - tend to reflect external magnetic fields by magnetizing in the opposite direction.
Important! Soft magnetic materials such as steel conduct magnetism when attached to a magnet, but this stops when it is removed. Permanent magnets are made from hard magnetic materials.
How does a permanent magnet work?
His work is related to atomic structure. All ferromagnets create a natural, albeit weak, magnetic field due to the electrons surrounding the nuclei of the atoms. These groups of atoms are able to orient themselves in the same direction and are called magnetic domains. Each domain has two poles: north and south. When a ferromagnetic material is not magnetized, its regions are oriented in random directions, and their magnetic fields cancel each other out.
To create permanent magnets, ferromagnets are heated at very high temperatures and exposed to strong external magnetic fields. This leads to the fact that individual magnetic domains inside the material begin to orient themselves in the direction of the external magnetic field until all domains are aligned, reaching the point of magnetic saturation. The material is then cooled and the aligned domains are locked into position. After removing the external MF, magnetically hard materials will retain most their domains, creating a permanent magnet.
Characteristics of permanent magnet
- Magnetic force is characterized by residual magnetic induction. Designated Br. This is the force that remains after the disappearance of the external MP. Measured in tests (T) or gauss (G);
- Coercivity or resistance to demagnetization - Ns. Measured in A/m. Shows what the external MF intensity should be in order to demagnetize the material;
- Maximum energy – BHmax. Calculated by multiplying the remanent magnetic force Br and coercivity Hc. Measured in MGSE (megaussersted);
- Temperature coefficient of residual magnetic force – Тс of Br. Characterizes the dependence of Br on the temperature value;
- Tmax – highest value temperature at which permanent magnets lose their properties with the possibility of reverse recovery;
- Tcur is the highest temperature value at which the magnetic material irreversibly loses its properties. This indicator is called the Curie temperature.
Individual magnet characteristics change depending on temperature. At different meanings temperature different types magnetic materials work differently.
Important! All permanent magnets lose a percentage of magnetism as the temperature rises, but with at different speeds depending on their type.
Types of permanent magnets
There are five types of permanent magnets, each of which is manufactured differently using materials with different properties:
- alnico;
- ferrites;
- rare earth SmCo based on cobalt and samarium;
- neodymium;
- polymer.
Alnico
These are permanent magnets consisting primarily of a combination of aluminum, nickel and cobalt, but may also include copper, iron and titanium. Due to the properties of alnico magnets, they can operate at the highest temperatures while retaining their magnetism, but they demagnetize more easily than ferrite or rare earth SmCo. They were the first mass-produced permanent magnets, replacing magnetized metals and expensive electromagnets.
Application:
- electric motors;
- heat treatment;
- bearings;
- aerospace vehicles;
- military equipment;
- high temperature loading and unloading equipment;
- microphones.
Ferrites
To make ferrite magnets, also known as ceramic, strontium carbonate and iron oxide are used in a ratio of 10/90. Both materials are abundant and economically available.
Due to their low production costs, resistance to heat (up to 250°C) and corrosion, ferrite magnets are one of the most popular magnets for everyday use. They have greater internal coercivity than alnico, but less magnetic strength than their neodymium counterparts.
Application:
- sound speakers;
- security systems;
- large plate magnets for removing iron contamination from process lines;
- electric motors and generators;
- medical instruments;
- lifting magnets;
- marine search magnets;
- devices based on the operation of eddy currents;
- switches and relays;
- brakes
Rare Earth SmCo Magnets
Magnets made of cobalt and samarium operate in a wide temperature range and have high temperature coefficients and high corrosion resistance. This view saves magnetic properties even at temperatures below absolute zero, making them popular for use in cryogenic applications.
Application:
- turbo technology;
- pump couplings;
- wet environments;
- high temperature devices;
- miniature electric racing cars;
- radio-electronic devices for operation in critical conditions.
Neodymium magnets
The strongest existing magnets, consisting of an alloy of neodymium, iron and boron. Thanks to their enormous power, even miniature magnets are effective. This provides versatility of use. Each person is constantly near one of the neodymium magnets. They are, for example, in a smartphone. The manufacture of electric motors, medical equipment, and radio electronics rely on ultra-strong neodymium magnets. Due to their ultra-strength, enormous magnetic force and resistance to demagnetization, samples up to 1 mm are possible.
Application:
- hard disks;
- sound-reproducing devices – microphones, acoustic sensors, headphones, loudspeakers;
- prostheses;
- magnetically coupled pumps;
- door closers;
- engines and generators;
- locks on jewelry;
- MRI scanners;
- magnetic therapy;
- ABS sensors in cars;
- lifting equipment;
- magnetic separators;
- reed switches, etc.
Flexible magnets contain magnetic particles inside a polymer binder. Used for unique devices where installation of solid analogues is impossible.
Application:
- display advertising – quick fixation and quick removal at exhibitions and events;
- signs Vehicle, educational school panels, company logos;
- toys, puzzles and games;
- masking surfaces for painting;
- calendars and magnetic bookmarks;
- window and door seals.
Most permanent magnets are fragile and should not be used as structural elements. They are manufactured in standard forms: rings, rods, disks, and individual: trapezoids, arcs, etc. Neodymium magnets due to high content iron are susceptible to corrosion, so they are coated on top with nickel, stainless steel, Teflon, titanium, rubber and other materials.
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Even in ancient times, people discovered unique properties certain stones - attracting metal. Nowadays, we often come across objects that have these qualities. What is a magnet? What is his strength? We will talk about this in this article.
An example of a temporary magnet is paper clips, buttons, nails, a knife and other household items made of iron. Their strength lies in the fact that they are attracted to a permanent magnet, and when the magnetic field disappears, they lose their properties.
The field of an electromagnet can be controlled using electric current. How does this happen? A wire wound in turns on an iron core changes the strength of the magnetic field and its polarity when a current is supplied and changed.
Types of permanent magnets
Ferrite magnets are the most famous and actively used in everyday life. This black material can be used as fasteners various items eg for posters, for wall boards used in office or school. They do not lose their attractive properties at temperatures not lower than 250 o C.
Alnico is a magnet consisting of an alloy of aluminum, nickel and cobalt. This gave it its name. It is very resistant to high temperatures and can be used at 550 o C. The material is lightweight, but completely loses its properties when exposed to a stronger magnetic field. Mainly used in the scientific industry.
Samarium magnetic alloys are high performance materials. The reliability of its properties allows the material to be used in military developments. It is resistant to aggressive environment, high temperature, oxidation and corrosion.
What's happened Neodymium magnet? It is the most popular alloy of iron, boron and neodymium. It is also called a supermagnet, as it has a powerful magnetic field with high coercive force. By observing certain conditions during operation, a neodymium magnet can retain its properties for 100 years.
Use of neodymium magnets
It is worth taking a closer look at what a neodymium magnet is? This is a material that is capable of recording the consumption of water, electricity and gas in meters, and not only. This type of magnet belongs to permanent and rare earth materials. It is resistant to fields of other alloys and is not subject to demagnetization.
Neodymium products are used in the medical and industrial industries. Also in domestic conditions they are used for attaching curtains, decorative elements, and souvenirs. They are used in search instruments and electronics.
To extend their service life, magnets of this type are coated with zinc or nickel. In the first case, spraying is more reliable, as it is resistant to aggressive agents and can withstand temperatures above 100 o C. The strength of the magnet depends on its shape, size and the amount of neodymium included in the alloy.
Applications of Ferrite Magnets
Ferrites are considered the most popular magnets among permanent species. Thanks to strontium included in the composition, the material does not corrode. So what is it - ferrite magnet? Where is it used? This alloy is quite fragile. That's why it is also called ceramic. Ferrite magnets are used in automotive and industrial applications. Used in various techniques and electrical appliances, as well as household installations, generators, and acoustic systems. In automobile manufacturing, magnets are used in cooling systems, window lifters, and fans.
The purpose of ferrite is to protect equipment from external interference and prevent damage to the signal received via the cable. Thanks to this, they are used in the production of navigators, monitors, printers and other equipment where it is important to obtain a clean signal or image.
Magnetotherapy
A procedure called magnetic therapy is often used and is carried out in medicinal purposes. The action of this method is to influence the patient's body using magnetic fields under low-frequency alternating or DC. This treatment method helps get rid of many diseases, relieve pain, strengthen immune system, improve blood flow.
It is believed that diseases are caused by disturbances in the human magnetic field. Thanks to physiotherapy, the body returns to normal and general state is improving.
From this article you learned what a magnet is, and also studied its properties and applications.
The magnetic properties of all other magnets are due to the magnetic moments of the electrons inside them. From the point of view of quantum field theory, the electromagnetic interaction is carried by a massless boson - a photon (a particle that can be represented as a quantum excitation of the electromagnetic field).
Weber - magnetic flux, when it decreases to zero, an amount of electricity of 1 coulomb passes through the circuit connected to it with a resistance of 1 ohm.
Henry - international unit inductance and mutual induction. If a conductor has an inductance of 1 H and the current in it varies uniformly by 1 A per second, then an emf of 1 volt is induced at its ends. 1 henry = 1.00052 10 9 absolute electromagnetic units of inductance.
Tesla- unit of measurement of magnetic field induction in SI, numerically equal to induction such a uniform magnetic field in which per 1 meter of length of a straight conductor, perpendicular to the vector magnetic induction, with a current of 1 ampere a force of 1 newton acts.
Use of magnets
- Magnetic storage media: VHS cassettes contain reels of magnetic tape. Video and audio information is encoded onto a magnetic coating on the tape. Also, in computer floppy disks and hard drives, data is recorded on a thin magnetic coating. However, storage media are not magnets in the strict sense, since they do not attract objects. Magnets in hard drives are used in drive and positioning motors.
- Credit, debit and ATM cards all have a magnetic stripe on one side. This band encodes the information needed to connect to financial institution and connections to their accounts.
- Conventional televisions and computer monitors: Televisions and computer monitors containing a cathode ray tube use an electromagnet to control a beam of electrons and form an image on the screen. Plasma panels and LCD displays use different technologies.
- Loudspeakers and microphones: Most loudspeakers use a permanent magnet and a current coil for conversion electrical energy(signal) into mechanical energy (the movement that creates sound). The winding is wound on a coil, attached to the diffuser and flows through it alternating current, which interacts with the field of a permanent magnet.
- Another example of the use of permanent magnets in audio engineering is in the pickup head of an electrophone and in the simplest tape recorders as an economical erasing head.
Magnetization
Demagnetization
Sometimes the magnetization of materials becomes undesirable and it becomes necessary to demagnetize them. Demagnetization of materials is achieved in various ways:
- heating a magnet above the Curie temperature always leads to demagnetization;
- A strong blow to the magnet with a hammer, or simply a strong blow, leads to demagnetization.
- place a magnet in an alternating magnetic field that exceeds the coercive force of the material, and then gradually reduce the effect of the magnetic field or remove the magnet from it.
The latter method is used in industry to demagnetize instruments, hard drives, erase information on magnetic cards, and so on.
Partial demagnetization of materials occurs as a result of impacts, since a sharp mechanical impact leads to domain disorder.
see also
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What is a magnet? Types of magnets. A magnetic field. A magnet is a body that can attract iron. Or: a magnet is an object made of a certain material that creates a magnetic field.
Magnet - what is it?
Magnets are made up of millions of molecules arranged in groups called domains. Each domain behaves like a mineral magnet, having a north and South Pole. When the domains have the same orientation, their strength combines to form a larger magnet. Iron has many domains that can be oriented in one direction, i.e. magnetize. Domains in plastic, rubber, wood and other materials are in a disordered state, their magnetic fields are multidirectional and therefore these materials cannot be magnetized.
Each magnet has at least one "north" (N) and one "south" (S) pole. Scientists agreed that the magnetic field lines come out of the "north" end of the magnet and enter the "south" end of the magnet.
If you take a piece of magnet and break it into two pieces, each piece will again have a "north" and a "south" pole. If you again break the resulting piece into two parts, each part will again have a “north” and a “south” pole. It doesn't matter how small the resulting pieces of magnets are, each piece will always have a "north" and a "south" pole. It is impossible to get it to form magnetic monopole(“mono” means one, monopole means one pole), that is, a piece with one pole.
Types of magnets
There are three main types of magnets:
- permanent (natural) magnets;
- temporary magnets;
- electromagnets.
Natural magnets, called magnetic ore, are formed when ore containing iron or iron oxides is cooled and magnetized by earth magnetism. Permanent magnets have a magnetic field in the absence of electric current because their domains are constantly oriented in the same direction.
Temporary magnets are magnets that act as permanent magnets only when they are in a strong magnetic field and lose their magnetism when the magnetic field disappears. Examples include paper clips and nails, as well as other “soft” iron products.
Electromagnets have a metal core with induction coil, along which it passes electricity.
What is a magnetic field?
A magnetic field is the area around a magnet within which the influence of the magnet on external objects is felt.
Human senses cannot see the magnetic field, but assistive devices prove that the magnetic field exists.
Sprinkle iron filings onto the paper and place a magnetic bar in the middle of the paper. The chips will move, forming arcs around the poles of the magnet. The pattern that the chips forms is a pattern of lines of the magnetic field of the magnetic bar.
Our Earth is surrounded by a magnetic field. This has always been the case, at least since the origin of the Earth. And everything that is on Earth, including people, animals and plants, is exposed to invisible power lines this field. But, at the same time, the human body has its own magnetic field, which arises as a result of the flow of blood through the vessels. IN different organs it may vary. In a healthy body and normal conditions there is complete correspondence and interaction of external and internal magnetic fields.
Magnetism is as necessary for all living things as water, air, food or sunlight. Its impact on terrestrial magnetism renders the Sun.
15.04.2017 18:46
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What is a magnet and why is it needed?
At your home, on the refrigerator door, you probably have beautiful pictures called magnets. Why are they called that? That's right, because they are held on the refrigerator by a magnet that is attached to the back side.
But the magnet is used not only to attach pictures to the refrigerator. Interested to know what else? We'll tell you about it. But first, let's talk about what a magnet actually is.
Its most famous property is the ability to attract metal objects to itself - paper clips, nails, needles, and basically anything, the main thing is that it is made of metal. This happens with the help of a force called magnetism.
Each magnet has two ends called north and south poles. The north pole of one magnet attracts the south pole of the other and then both of them become magnetized. By the way, our planet Earth is also a giant magnet, which has two poles, which are located at the top and bottom of the planet.
There are three main types of magnets - permanent; temporary; and electromagnets. You probably want to ask where they come from?
Permanent magnets are made from natural materials such as iron, ceramics, cobalt, etc.
Temporary magnets are those that have their magnetic (attracting) properties only in the vicinity of permanent magnets. Thus, any metal objects can be considered temporary magnets - scissors, paper clips, pins, etc.
An electromagnet is a coil on which a metal wire is tightly wound. Such a magnet works only if an electric current passes through a wire wound on a coil and gives it magnetic, attractive properties.
The attractive force of an electromagnet depends on changes in the magnitude and direction of the electric current passing through the wire. That is, the more powerful the current, the stronger magnet attracts. However, an electromagnet can only work if electricity is connected. Once the electricity is turned off, it loses its power.
Magnets are a very useful thing. For example, they are needed to ensure that the doors of our refrigerators close tightly. Or to collect needles scattered on the floor without getting pierced.
And huge magnets are used in various factories. They are fixed to a crane and thanks to this, heavy metal parts are moved.
The compass needle is also a tiny magnet, so it always points in the direction North Pole. With the help of a compass, people find their way to any part of the Earth. They are used not only on the ground, but also on airplanes and ships.
To understand how they work magnetic poles, you can conduct a simple experiment: take two magnets in your hands and try to press them one against the other.
Different poles (north and south) attract each other. And the same ones (north and north or south and south) repel each other. You will feel this when you begin to bring the magnets closer to each other.
Also, at home you can conduct another interesting experiment called “Floating Compass”. To do this, take (or rather ask your mother) an ordinary sewing needle and magnetize it.
How to do it? To give a needle the properties of a magnet, you need to run a magnet over it approximately 50 times in the same direction. After this, stick a needle into a piece of cork. Place the cork in a bowl of water.
That's all. When the needle calms down, you will see that it is always directed only in one direction - to the north.