A magnet is an object that is capable of creating a magnetic field. All magnets must have at least one north pole, and one south pole.
Most people are familiar with the basic traits of magnets, and know that they attract metal objects. Specifically, magnets attract objects made from iron, nickel, and cobalt. However magnets are used in many other ways due to the fact that they are able to effect electrically charged particles and electric conductors. Because of these properties, magnets are capable of converting electrical energy to mechanical energy, and vice-versa.
Some practical uses of this capability are found in the thousands of different products that rely on magnets to operate, such as loudspeakers, generators, microphones, motors, eddy current and hysteresis torque devices, magnetic resonance equipment, sensors, gauges, switches – etc.
A magnetic field is an area of space where there is a detectable magnetic force. A magnetic force has a measurable strength and direction.
Magnetism refers to the force of attraction or repulsion that exits between substances made of specific materials such as iron, nickel, cobalt and steel. This force exists due to the motion of the electrical charges within the atomic structure of these materials.
A permanent magnet continues to emit magnetic force even without a power source, whereas an electromagnet requires power in order to generate a magnetic field. EAM only offers permanent magnets.
A permanent magnet will retain its magnetism unless it is affected by a strong outside magnetic or electrical force, or elevated temperatures. If they are not exposed to any of these conditions, permanent magnets will lose magnetism on their own, however this degradation is very slow, on the order of one percentage point every ten years or so.
Yes, if a magnet is influenced by another strong magnet, is affected by a powerful electrical force, or is exposed to temperatures above a certain level, it may lose some or all of its magnetic strength. Be sure to identify the properties of the magnet in question before using it if loss of strength is a concern.
Depending on how the magnet in question lost its strength, it may be able to be re-magnetized. Once a magnet is fully saturated, it cannot be made any stronger.
An isotropic magnet is not oriented during the manufacturing process, and can therefore be magnetized in any direction after it is made. In contrast, an anisotropic magnet is exposed to a strong magnetic field during the manufacturing process in order to orient the particles in a specific direction. As a result, anisotropic magnets can only be magnetized in one direction, however they generally have stronger magnetic properties.
If allowed to move freely, a magnet will align itself with the north-south polarity of the earth. The pole that seeks south is called the “south pole” and the pole that points north is called the “north pole.”
The poles of a magnet are identical, so you cannot see or feel the difference between them. An easy way to check the poles of a magnet is to use a compass. The part of the needle that normally points north will seek the south pole of the magnet.
Magnets are made using the following methods:
- Pressing and Sintering
- Extruding
- Injection Molding
- Calendering
- Casting
- Compression Bonding
Permanent magnets may be made from any for the following materials:
- Strontium-Iron (Ferrite or Ceramic)
- Neodymium-Iron-Boron (Sintered or Injection Molded)
- Samarium Cobalt (a type of Rare Earth)
- Aluminum-Nickel-Cobalt (Alnico)
When a magnet is incorporated into a housing or permanently mounted to another part it may be called a magnetic assembly. The most common types of magnetic assemblies are those that are designed to increase the pull strength that the magnet would normally exhibit. Some magnetic assemblies, like round bases or channel assemblies, can be more than 30 times as strong as the magnet would be on its own.
Magnetic strength is measured in a few different ways. Here are a few examples:
A Gauss Meter is used to measure the strength of the field a magnet emits in units called “gauss.”
Pull Testers can be used to measure the amount of weight a magnet can hold in pounds or kilograms.
Permeameters are used to identify the exact magnetic characteristics of a specific material.
There are several reasons EAM is the right choice for you:
QUALITY: EAM is an ISO/TS 16949:2009 certified manufacturer. You can count on our highly developed quality system to see your parts or project through from design through final delivery.
EXPERIENCE: EAM’s customer service and technical team has decades of experience with nearly every type of magnetic application. You can be assured that we will apply that experience to your specific needs each and every time to guarantee your complete satisfaction.
TECHNICAL SUPPORT: EAM has the technical expertise to help you through your most difficult magnetic design challenges. Our helpful and courteous staff is always available to get you the answers you need, as quickly and accurately as possible.
VERSATILITY: No other magnet company can offer customers what EAM can: a unique combination of TS certified, domestic magnet manufacturing capability, including on-site magnetization, fabrication, design and analysis – as well as high quality off-shore sourcing options which provide our clients the best, most cost-effective options no matter what the requirements.
AlNiCo
Permanent magnets based upon alloys containing aluminum, nickel, cobalt, iron + additions. They are very stable materials and are not sensitive to moderate temperature changes or mildly corrosive environments.
Anisotropic
When magnetic properties are intrinsically stronger in a preferred direction. Higher flux levels are available in the direction of magnetic orientation.
A.S.T.M.
American Society for the Testing of Materials.
Bhmax
Maximum energy product of a magnet. A descriptive term to quantify the potential power of a magnet material (kȷ/m3 equals 0.1256 MGOe).
C.G.S.
The system of units based on centimeter, gram and second.
Coercive Force, Intrinsic (Hcȷ)
The magnetizing field required to reduce the intrinsic magnetization ȷ to zero.
(1 A/m = 0.01256 Oe)
Coercive Force, Normal (HcB)
The magnetizing field required to reduce the normal magnetization B to zero.
(1 A/m = 0.01256 Oe)
Curie Temperature (Tc)
The temperature above which a magnetic material ceases to have any ferromagnetic properties. In practice this is much higher than the useful maximum operating temperature of a permanent magnet.
De-magnetisation
Process to reduce the flux within a permanent magnet to either a set limit or to zero. Can occur through exposure to high DC or AC magnetic fields, or by heating to temperatures near to or above the Curie temperature.
De-magnetisation Curve
The curve which describes the demagnetization of a permanent magnet in the second quadrant of its hysteresis loop after first being magnetized. Both the intrinsic and normal curves may be shown. Among other important data, the curves yield Br, BHmax, Hcȷ and HcB.
Diamagnetic Materials
Materials which have a permeability which is very slightly negative and opposes the application of the magnetic field. Examples are copper, silver and gold.
Dimensional Ratio
The ratio of the mean length of the magnet to its diameter. For a magnet in an open circuit the dimensional ratio can be related to the B/H ratio.
Electro-Motive Force (e.m.f.)
The term used to describe the quantity of work per unit charge which is quantified as the volt (V).
Ferrimagnetic Materials
An important class of magnetic materials. They behave like feral magnets in that they display high permeability and hysteresis. Typically they have lower saturation magnetization and are produced in the form of magnetic oxides.
Ferrite Material
Ferrite magnets are ferrimagnetic and may be either “hard” (permanent) or “soft”. In the case of permanent magnets they are based on a mixture of barium, strontium and iron oxide. They can be produced using a sintering or plastic bonding process. They may be isotropic or anisotropic.
Ferromagnetic Materials
These are the only materials which have a high spontaneous magnetization. This is due to a special combination of electron spins and separation of atoms. The permeability may be more than 1 million times that of the dire and paramagnetic materials. Iron, nickel and cobalt other well-known metals which have high permeability at room temperature. Some of the rare earth (lanthanide) metals are ferromagnetic – but only at low temperatures. An important sub-class of ferromagnets are the ferrimagnets. These are materials which show ferromagnetic type behavior but are typified by having lower saturation.
Fluxmeter
An instrument for measuring the total magnetic flux produced in a specific area. Most often a heavily damped electronic voltage integrator.
Gauss
The C.G.S. unit of magnetic flux density.
Gaussmeter
An instrument for measuring instantaneous values of magnetic flux density at a point in space. They usually incorporate all affect probes.
Henry (H)
The S. I. unit of mutual inductance derived from Weber per ampere (Wb/A).
Hysteresis Loop
A closed curve which describes the relationship between magnetic flux density B and magnetizing field H for a ferromagnetic material. The area contained within the loop is related to specific energy and is an important magnetic parameter.
I.E.C.
International Electrotechnical Commission. A body which creates world standards for magnetic materials and test methods.
Irreversible Losses
The loss in the flux density when a magnet is partially the magnetized by being at a temperature and operating point to severe to sustain linear behavior. Re-magnetization is the only way to recover these losses.
Isotropic
A non-oriented magnetic material which has similar physical and magnetic properties in all directions.
Leakage Factor
Accounts for the flux leakage from the magnetic circuit. Is the ratio between the maximum magnetic flux in the circuit and the average useful flux in the air gap and is usually a value between 2 and 20.
Leakage Flux
The flux whose path is outside the intended magnetic circuit.
Load Line
A line drawn from the origin of a hysteresis loop to the operating point of a magnetized magnet or system. In dynamic magnetic circuits this is a variable.
Magnetic field strength (H)
The m.m.f. per unit length. The S. I. unit of magnetic strength is the ampere per meter (A/m).
Magnetic flux (Φ)
The S. I. unit of magnetic flux is the weber. (1 weber = 108 maxwell (C.G.S.)). Is the amount of magnetic flux which when reduced steadily to zero in one second produces an e.m.f. of 1 volt in a one turn coil.
Magnetic Flux Density (B)
The magnetic flux passing through a unit area. (Unit: tesla = weber/m2 ).
Magnetic Induction (see Magnetic Flux Density)
Magnetic Materials
All materials are by definition “magnetic” and they are classified by their response to the application of a magnetic field (permeability or susceptibility). Essentially, the permeability or susceptibility depends upon the electron spin around the nuclei of atoms and their inter-atomic separation.
Magnetic Materials in Industry
Depending upon which ally or processing route is followed, ferromagnetic materials can be produced as permanent magnets or soft magnetic materials. For example alloys of iron, aluminum, cobalt and nickel are the basis for the “AlNiCo” family of permanent magnets and alloys based upon iron and the rare earth metal, neodymium, are the basis of the so-called “NdFeB” magnets. Alloys of iron with nickel, silicon, cobalt or chromium form the basis for the world-wide soft magnets industry for applications which require properties beyond those of iron or low carbon steels. For the ferrimagnetic class of magnets, examples are barium and strontium ferrite’s used as permanent magnets manganese or nickel ferrite used in soft magnetic cores and уferric oxide white in magnetic recording.
Magnetizing
The process to charge a permanent magnet before it can be useful. The magnetizing field can be applied by a permanent magnet, and electromagnet or a post solenoid.
Magnetomotive force (m.m.f.)
The total magnetic potential difference across a given length expressed as Ampere (A) in S. I. units
Maximum Permeability (µmax)
For a soft magnetic material it is the peak value obtained for B/H. It is a widely used control parameter when specifying such material.
Maxwell (M)
-8 The C.G.S. unit of magnetic flux. (1 maxwell = 10-8 weber)
Neodymium Iron Boron (NdFeB)
A general term to describe the family of magnets based on the tetragonal Nd2Fe14B compound. Magnets may be fully dense or polymer bonded. They have the highest room temperature energy product.
Oersted (Oe)
The C.G.S. unit of magnetic field strength. (1 Oe = 1000/4π ≡ 79.6 A/m).
Operating Point
The operating point is the crossing between load line and the de-magnetization curve.
Orientation
The preferred direction of magnetization of a permanent magnet. The material may be physically aligned through pressing or heat treatment during manufacture.
Paramagnetic Materials
Materials which have a slight positive permeability. Examples are aluminum, platinum and manganese.
Permanent Magnetic Material
A material which may be relatively easy or hard to magnetize but is very difficult to demagnetize. Permanent magnets are compounds which possess a strong resistance to rotation of the magnetization away from the preferred direction. This may be achieved by crystal anisotropy or by inclusion of the main wall pinning mechanisms.
Permeability (µ)
The general term to express the relationship between magnetic flux density and applied magnetic field strength, i.e. the instantaneous value of B/H.
Permeability of free space (µo)
The defined constant for B/H in a vacuum equivalent to 4π x 10-7H/m.
Recoil Permeability (µrec)
The slope of the recoil loop on the hysteresis curve for a permanent magnet material. For hard ferrite and a rare earth materials this value may be constant and close to unity. For alnico materials is likely to be between 1.8 and 6.0.
Reluctance
The resistance of the magnetic circuit to the passage of flux.
Reluctance loss factor
A constant for a given design usually between 1.1 to 1.5.
Remanence
The flux density (Br or ȷr ) which remains in a magnetic material in a closed magnetic circuit after magnetization but with the field removed.
Remanent Flux Density
The flux density which remains in a magnetic material after magnetization and conditioning for final use.
Reversible Losses
The reversible loss in flux density of a magnet when it is subjected to higher temperatures. Related to the temperature coefficient.
Samarium Cobalt (SmCo)
Samarium Cobalt is the name given to families of materials based on the SmCo and Sm2Co17 alloys. They are characterized by their high magnetic strength at elevated temperatures.
S.I.
The System International unit agreement based on the meter, kilogram and second.
Soft Magnetic Material
A term which describes a magnetic material which is both easy to magnetize and to demagnetize. The intrinsic structure of these materials is such that they are easy to magnetize in all directions.
Temperature coefficient
A value which describes the change in magnetic property with a change in temperature. Usually expressed as percentage change per unit of temperature.
e.g., for the temperature coefficient of a remanence
A similar expression can be used for coercivity (HcB, Hcȷ) or energy product (Bhmax).
Temperature coefficients are not linear but can be treated as such when operating temperatures are much lower than the Curie temperature.
Tesla (T)
The S.I. unit of magnetic flux density. (1 tesla = 10,000 gauss).
Weber (Wb)
The amount of flux which when gradually reduced to zero includes 1 volt in a single turn coil in one second. (1 weber = 108 maxwell).
Magnetic Theory and Applications
All materials are defined as being magnetic in that they respond to the application of an applied magnetic field
Comparison of Maximum Operating Temperatures
EA Magnetics carries a wide range of sizes in almost all magnetic materials. The following chart can be used
Testing Magnets
A test or combination of test methods should be based upon the criticality of the requirement, and the cost and
Comparison of Magnetic Strength
We offer a wide range of sizes in Sintered Samarium Cobalt, Sintered Neodymium and Compression
Magnetic Strength Over Distance
A resource explaining how the strength of a magnetic field drops off over distance. Distance, x Field at Distance
Magnet Design Considerations
When choosing a magnet material for your application, a number of considerations must be taken into account.
Magnetization Types
Various magnetisation configurations are possible which depend upon the material type and whether isotropic or anisotropic.