Magnetic Property

When I was new to this industry, I have confusions between magnetic flux density, magnetic flux and residual flux density.   So, what's the meaning and difference between them?Magnetic Flux Density: lines of flux per unit area, usually measured in Gauss (CGS). One line of flux per square centimeter is one Maxwell. Gaussmeter Surface magnetic flux density refers to a measurement point, actually, it is the value of a small measurement area, and the magnetic field distribution of the magnet changes, so the surface magnetism at different points is generally different. For applications that require the use of space magnetic fields, surface magnetic flux density or the magnetic induction intensity value at a specified point is usually regarded as an important technical requirement.  The surface magnetism is related to the height-to-diameter ratio of the magnet (the ratio of the height to the diameter of the magnet. The default height or thickness here is the magnetization direction of the magnet). The greater the height-to-diameter ratio, the higher the surface magnetism, that is, the greater the surface area perpendicular to the magnetization direction., the lower the surface magnetism; the larger the size of the magnetization direction, the higher the surface magnetism. In addition, the Hall elements on the Gaussmeters of different manufacturers are different, and the surface magnetism measured for the same magnet is also slightly different. Magnetic Flux - Is a contrived but measurable concept that has evolved in an attempt to describe the “flow” of a magnetic field. When the magnetic induction, B, is uniformly distributed and is normal to the area, A, the flux, Ø = BA. FluxmeterThe measuring instrument for magnetic flux is a flux meter. With the Helmholtz coil, it can not only measure the magnetic flux, but also calculate its magnetic moment, because the measured value of the magnetic flux will change with the parameters of the flux meter and the Helmholtz coil. Variety. Magnetic flux and magnetic moment are more like the difference between weight and mass. Weight is affected by the gravitational constant. The weight of the same object on Earth and Mars is different, but the mass is the same. Affected by the number of turns of the coil, the magnetic flux of the same magnet measured by different flux meters and coils may be different, but the magnetic moment must be the same.When the magnet is in an open-circuit state, the actual residual magnetization value Bdi (also called essential magnetic flux density) corresponding to the operating point can be calculated by converting magnetic flux into magnetic moment. Bdi=Φ*coil constant/magnet volume. Residual magnetic flux density, surface magnetic flux density and magnetic flux are three concepts that are easily confused. Let’s clarify them here:• Residual magnetism is an essential property of materials. As long as self-demagnetization does not occur, the residual magnetism of a magnet remains unchanged. It is determined by the product's raw material formula and preparation process. The test is conducted in a completely closed circuit state. • Surface magnetic flux density is the magnetic induction intensity value at the measurement location (a small area) when the magnet or magnetic component is in an open circuit or semi-open circuit state. Surface magnetic flux density is a directional vector, and the surface magnetic flux density data on different surfaces of the magnet are very different. We usually refer to the surface magnetic flux density value perpendicular to the magnetic pole surface. The maximum surface magnetic flux density of a single magnet is one-half of the residual magnetic flux density. Note that it is a "single magnet". In some magnetic components and magnet arrays, special magnetic circuit designs can be used to increase the magnet's surface magnetism. Its value can even exceed the remanence.• Magnetic flux is the overall magnetic size of the magnet measured through coil testing. Usually, magnetic assemblies are not suitable for testing magnetic flux. Magnetic flux also has direction requirements by default. Of course, the total magnetic flux value can also be measured using a three-dimensional Helmholtz coil during actual measurement. Special attention needs to be paid to the test direction when measuring surface magnetism and magnetic flux.Hangzhou Vector Magnets tests from appearance to function to ensure quality from raw material to end product. Material Test ICP O/N/H-3000 C/S-2800 BH curve tester VSM PFM SEM Lazer particle analyzer Dimension test 3D-Coordinator CCD Keyence OGP Property test automatic magnetizing and inspection magnetic angle  deviation automatic test surface magnetic flux density tester 3D magnetic property inspection magnetic angle diviation test magview magnetic flux tester 3D Hemholz coil Other test gloss tester colorimeter roughness tester aging tester PCT metallographic analyzer RoHs2.0

We all know that the four parameters Br/Hcb/Hcj/Bhmax are the main parameters of magnet material performance. The engineer of magnet application design selects the appropriate magnetic material according to the electromagnetic conversion corresponding to these parameters. After the magnet is prepared, we can obtain these parameters by testing the demagnetization curve, and there are some other parameters on the demagnetization curve that are also very important for the application of the magnet, such as HK.The second quadrant of the demagnetization curve is the commonly used J-H curve, which is the correlation curve between the magnet's magnetic polarization intensity J and the external magnetic field intensity H, which can reflect the changes in the internal magnetic properties of the magnet. When the magnetic polarization intensity J on the J-H curve is 0, the corresponding magnetic field intensity is called the intrinsic coercivity Hcj. The value of intrinsic coercivity reflects the size of the anti-demagnetization ability of the permanent magnet material. From the J-H graph, we can find that when the external magnetic field keeps increasing, the magnetic induction intensity/magnetic polarization intensity of the magnet decreases very slowly, but when the external magnetic field is greater than a certain value, the magnetic induction intensity of the magnet decreases rapidly. We reduce this by 10% (or 5%) of the magnet’s magnetization, which requires the application of a reverse magnetic field, called Knee coercive force, which is HK. After the external magnetic field exceeds the tolerance of HK, it will cause a large Irreversible magnetic loss, magnet application designers are very concerned about this point. Usually we can see the ratio of HK/Hcj from the demagnetization curve. This ratio is called squareness. Generally, we consider magnets with squareness greater than 90% to be qualified. Hk/Hcj is also one of the important magnetic properties of permanent magnets. Like μrec, it characterizes the stability of the magnet under dynamic working conditions. HK/Hcj=1/μrec, the squareness is inversely related to the magnet's recovery permeability μrec. The larger the HK/Hcj, the closer the recovery permeability μrec is to 1, and the material's ability to resist interference from external magnetic fields and environmental temperature factors is better. The stronger, the better its stability. Therefore, increasing HK has greater practical significance for high-temperature applications such as motors.

What is Heat Treatment Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing techniques, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but  changing the workpiece inside microstructure  or changing the chemical composition on the surface of the workpiece , improve the performance of the workpiece. Its characteristic is to improve the inherent quality of the workpiece, which is generally not visible to the eye. In order to make the metal workpiece have the required mechanical properties, physical properties and chemical properties, in addition to the reasonable selection of materials and various forming processes, heat treatment processes are often essential. Annealing, normalizing, quenching and tempering are the four basic processes in the overall heat treatment.             Four Basic Heat Treatment Processes Annealing Annealing is to heat the workpiece to an appropriate temperature, use different holding times according to the material and the size of the workpiece, and then slowly cool down, the purpose is to make the internal structure of the metal reach or near the equilibrium state, to obtain good process performance and performance, or Further quenching for organizational preparation. Normalizing Normalizing is to heat the workpiece to a suitable temperature and cool it in the air. The effect of normalizing is similar to annealing, except that the resulting structure is finer. It is often used to improve the cutting performance of the material, and sometimes it is used for low requirements parts as the final heat treatment. Quenching Quenching is to quickly cool the workpiece in the quenching medium such as water, oil or other inorganic salts, organic aqueous solution after heating and heat preservation. After quenching, the steel parts become hard, but at the same time they become brittle. Tempering Tempering is to keep the quenched steel parts at an appropriate temperature higher than room temperature and lower than 710 ℃ for a long time, and then cool them, which can reduce the brittleness of the steel parts

High temperature SmCo magnets that can withstand temperatures of 500°C and 550 °C          Many key devices in the aerospace and other fields, such as aircraft motors and generators, microwave function tubes, magnetic bearings and inertial navigation devices, require high-performance high-temperature permanent magnet materials.         Among the existing permanent magnet materials, the strongest NdFeB magnet has the highest room temperature performance, but its Curie temperature is 312 °C, and the maximum working temperature is usually not more than 250 °C; the Curie temperature of AlNiCo magnet is 850 °C , The maximum operating temperature can reach 520 °C, but the coercive force of the magnet is very low ( 145 kA / m), so it can not manufacture small and light components; SmCo magnet has a high Curie temperature (750 ~ 920 °C), Moreover, it has strong magnetocrystalline anisotropy and high coercivity at room temperature ( 1990 kA / m), which is the first choice for high temperature permanent magnet material.         The main reason why the traditional 2:17 SmCo magnet is not suitable for high temperature applications is that its coercive force decays rapidly with increasing temperature (coercive force temperature coefficient β ≈-0.30% / °C). By adjusting the alloy composition and heat treatment process of the traditional 2:17 type SmCo magnet , the microstructure and microcomposition inside the material are controlled to reduce the temperature coefficient of the coercive force of the material and increase the use temperature. In the end, we successfully made a 2:17 type SmCo high temperature magnet that can be applied at 500 ° C and 550 ° C.

“Split” is probably a more common word than “divided” in this context. If an atom has a net angular momentum (due to spin and orbital angular momenta of its constituent particles) then it also has a net magnetic dipole moment. The energies corresponding to the different possible quantized orientations of this magnetic moment in the magnetic field are seen as small increases or decreases in the transition energies between two states of the atom. Even if the net angular momentum and magnetic moment are zero, in a very strong magnetic field the magnetic moments of the constituent particles will interact independently with the magnetic field, producing a different splitting pattern than the pattern that is observed in a weak magnetic field.By - Mel Siegel, from Carnegie Mellon University

All materials have tiny internal magnetic fields called domains, but in these three ferromagnetic metals, the internal magnetic domains are uniformly aligned to give them a magnetic field. In all other elements, the internal magnets are either randomly oriented or cancel each other out, which is why these other metals don't have a magnetic field.The ferromagnetic metals are often combined with other metals to create alloys, which also have magnetic properties. For instance, steel is an alloy made from iron that is magnetic, although not to the same degree as pure iron.Most magnets are made from one of these three metals, which is then heated until the metal reaches its specific Curie temperature. The Curie temperature is the specific temperature at which a ferromagnetic metal takes on the properties of a magnet. If the material is only heated to the exact Curie temperature, the magnetic effects are only temporary. The magnetic properties can be made more permanent by heating the metal up beyond this temperature.

It depends on a bunch of factors like the type of magnetic material, the temperature, and whether it's stored with a "keeper" of easily magnetizable material that creates a magnetic circuit. A bar magnet out in the open tends to be in a metastable state. Magnetic field lines go in circles, but they don't "like" to go through air and and other non-magnetic materials, so this creates Magnetic reluctance which tends to demagnetize the magnet. Good magnetic materials have high Coercivity which means they resist the demagnetizing, but this decreases with temperature and disappears entirely at the Curie temperature. If you complete a Magnetic circuit using either more high coercivity material magnetized in the same direction (in a loop), or more low-coercivity, high-susceptibility material such as soft iron (which happily picks up magnetism so as to create a loop), the demagnetizing is much less.However potentially it can last a very long time: hundreds of millions of years. Igneous rocks that have not been reheated often contain a record of the earth's magnetism frozen in at the time they were formed. In conjunction with the fact that there have been Geomagnetic reversals at irregular intervals, this can be used as a method of dating rocks, and was key to establishing Seafloor spreading, which is part of the modern theory of Continental drift

Let's see the picture below.  The field on the other side of the plate is almost nil.  This is because the plate has diverted the field, causing a lot of it to flow within the plate itself instead of in the air. This is sometimes used to help shield a speaker from your TV set.  Placing the speaker in a box lined with sheet steel prevents the speaker magnet from messing with the colors on your TV screen.  Or, the speaker manufacturer may place shielding around the speaker magnet itself - much smaller and more effective.    

Some important properties used to compare permanent magnets are: remanence (Br), which measures the strength of the magnetic field; coercivity (Hci), the material's resistance to becoming demagnetized; energy product (BHmax), the density of magnetic energy; and Curie temperature (Tc), the temperature at which the material loses its magnetism. Rare earth magnets have higher remanence, much higher coercivity and energy product, but (for neodymium) lower Curie temperature than other types. The table below compares the magnetic performance of the two types of rare earth magnet, neodymium (Nd2Fe14B) and samarium-cobalt (SmCo5), with other types of permanent magnets. Magnet Br (T) Hci (kA/m) (BH)max (kJ/m3) Tc (°C) Nd2Fe14B (sintered) 1.0–1.4 750–2000 200–440 310–400 Nd2Fe14B (bonded) 0.6–0.7 600–1200 60–100 310–400 SmCo5 (sintered) 0.8–1.1 600–2000 120–200 720 Sm2Co17 (sintered) 0.9–1.15 450–1300 150–240 800 Alnico (sintered) 0.6–1.4 275 10–88 700–860 Sr-ferrite (sintered) 0.2–0.4 100–300 10–40 450

You can strengthen magnets by placing them inwater, stacking them on top of each other or recharging them. The method of making amagnet stronger depends on the type of magnet you have. To strengthen an iron bar magnet, fill a bowl or panwith water. Find a small item to float in the water and place the magnet on topof the item. The magnet starts to twirl in the water until it rests and pointsdirectly north/south. Remove the magnet from the water and keep it in the sameposition while placing it on a hard surface. Then, strike one end of the magnetwith a hard object repeatedly. The force can loosen small magnetic domains inthe bar. You can recharge a magnet that has lost its strengthby repeatedly rubbing it against a very strong magnet. The strong magnet's pullrealigns the magnetic domains in the weaker magnet.The last option to strengthen magnets is to stack allthe weak magnets together. This can be difficult, as magnets attract inopposite directions. For this method to be effective, you must clamp or holdthe magnets together so they all face the same direction.

Magnetic field strengthis one of two ways that the intensity of a magnetic field can be expressed.Technically, a distinction is made between magnetic field strength H, measured in amperes per meter (A/m), and magnetic flux density B, measured in Newton-meters per ampere (Nm/A), also called teslas (T).The magnetic field can be visualized as magnetic field lines. The field strength corresponds to the density of the field lines. The total number of magnetic field lines penetrating an area is called the magnetic flux. The unit of the magnetic fluxis the tesla meter squared (T · m2, also called the weber and symbolized Wb).The older units for the magnetic flux, the maxwell (equivalent to 10-8 Wb), and for magnetic flux density, the gauss (equivalent to 10-4 T), are obsolete and seldom seen today.

In most applications, the answer is simply "no". If the magnets will be exposed to higher temperatures while in repelling applications, the answer is "possibly". The exact answer isa bit too complicated for a FAQ answer. We'd like to hear from your detailed question.

Very little. Neodymium magnets are thestrongest and most permanent magnets known to man. If they are not overheated or physically damaged, neodymium magnets will lose less than 1% of their strength over 10 years - not enough for you to notice unless you have very sensitive measuring equipment. They won't even lose their strength if they are held in repelling or attracting positions with other magnets over long periods of time.

Yes.  Neodymium-Iron-Boron magnets are sensitive to heat. If a magnet heated above its maximum operating temperature (176°F (80°C) for standard N grades) the magnet will permanently lose a fraction of its magnetic strength.If they are heated above their Curie temperature (590°F (310°C) for standard N grades), they will lose all of their magnetic properties. Different grades of neodymium different maximum operating and Curie temperatures.