TEMPERATURE

Temperature

Temperature sensitivity varies, but when a magnet is heated to a temperature known as the Curie point, it loses all of its magnetism, even after cooling below that temperature. The magnets can often be remagnetized, however.

Additionally, some magnets are brittle and can fracture at high temperatures.

The maximum usable temperature is highest for alnico magnets at over 540 °C (1,000 °F), around 300 °C (570 °F) for ferrite and SmCo, about 140 °C (280 °F) for NIB and lower for flexible ceramics, but the exact numbers depend on the grade of material.

Rare-earth magnets

Rare-earth magnets

Rare earth (lanthanoid) elements have a partially occupied f electron shell (which can accommodate up to 14 electrons). The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore, these elements are used in compact high-strength magnets where their higher price is not a concern. The most common types of rare-earth magnets are samarium-cobalt and neodymium-iron-boron (NIB) magnets.

ALNICO

Alnico

Alnico magnets are made by casting or sintering a combination of aluminium, nickel and cobalt with iron and small amounts of other elements added to enhance the properties of the magnet. Sintering offers superior mechanical characteristics, whereas casting delivers higher magnetic fields and allows for the design of intricate shapes. Alnico magnets resist corrosion and have physical properties more forgiving than ferrite, but not quite as desirable as a metal. Trade names for alloys in this family include: Alni, Alcomax, Hycomax, Columax, and Ticonal.^[21]

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Demagnetizing ferromagnets

Demagnetizing ferromagnets

Magnetized ferromagnetic materials can be demagnetized (or degaussed) in the following ways:

• Heating a magnet past its Curie temperature; the molecular motion destroys the alignment of the magnetic domains. This always removes all magnetization.
• Placing the magnet in an alternating magnetic field with an intensity above the material's coercivity and then either slowly drawing the magnet out or slowly decreasing the magnetic field to zero. This is the principle used in commercial demagnetizers to demagnetize tools and erase credit cards and hard disks and degaussing coils used to demagnetize CRTs.
• Some demagnetization or reverse magnetization will occur if any part of the magnet is subjected to a reverse field above the magnetic material's coercivity.
• Demagnetisation progressively occurs if the magnet is subjected to cyclic fields sufficient to move the magnet away from the linear part on the second quadrant of the B-H curve of the magnetic material (the demagnetisation curve).
• Hammering or jarring: the mechanical disturbance tends to randomize the magnetic domains. Will leave some residual magnetization.

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Magnetic pole

Magnetic pole

Although for many purposes it is convenient to think of a magnet as having distinct north and south magnetic poles, the concept of poles should not be taken literally: it is merely a way of referring to the two different ends of a magnet. The magnet does not have distinct north or south particles on opposing sides. If a bar magnet is broken into two pieces, in an attempt to separate the north and south poles, the result will be two bar magnets, each of which has both a north and south pole.

However, a version of the magnetic-pole approach is used by professional magneticians to design permanent magnets. In this approach, the divergence of the magnetization ∇•M inside a magnet and the surface normal component M•n are treated as a distribution of magnetic monopoles. This is a mathematical convenience and does not imply that there are actually monopoles in the magnet. If the magnetic-pole distribution is known, then the pole model gives the magnetic field H (see also Demagnetizing field). Outside the magnet, the field B is proportional to H, while inside the magnetization must be added to H(see Units and calculations). An extension of this method that allows for internal magnetic charges is used in theories of ferromagnetism (see micromagnetics).

Magnetism

Magnetism has been known since ancient Greece as the ownership 

of certain minerals such as magnetite (so named because it was discovered 

in the Greek region called Magnesia) to attract pieces of iron. They are natural

 magnets.It appears that it was the Chinese who first used magnets as compasses in the 

twelfth century.Petrus Peregrinus (Pierre de Maricourt), a French crusader, in 1269 found that if

 a needle is left freely on a spherical magnet, it is oriented along lines passing

 through points located at opposite ends of the field. By analogy, states north and 

south poles of the magnet, and found that the north pole andsouth pole attract, like poles repel it, and that the fragment a piece of magnetite, 

magnetic poles are still appearing.Magnetite crystalsIn the s. XVI, William Gilbert (physician to Queen Elizabeth), artificial magnets

 produced by rubbing pieces of iron and magnetite. He also suggested that the

 operation of the compass was due to the magnetic properties of the Earth.There are some creatures that have magnets inside that work like compasses.

 It is called magnetism. It seems that this phenomenon is the ability to orient migrating birds.Some bacteria naturally synthesize grains of magnetite (iron oxide, Fe3O4 formula)

 with a single domain, which are aligned and give rise to microscopic compass,

 allowing them to navigate.Found magnetite crystals inside the skull of the pigeon, connected to many nerves.

As a result, the pigeons know longitudinally oriented magnetic field, ie north-south 

and east-west, as well as the latitude, ie according to the inclination of the field. Also

 magnetic substances have been found in other organisms such as bees, monarch

 butterflies, moles, turtles and even in human brain tissue.One of the many applications of magnetic fields are the magnetic stripes on credit 

cards, phone ... They keep the information through the tiny magnetic domains. The 

reader consists of a small coil which induces an electric current to the passage of

 the card. So often damaged the card when it comes to intense magnetic fields.In ancient times the magnetite attributed many properties. Was supposed to cure

 rheumatism and gout and allowed to speak with the gods. In the sixteenth century

 Paracelsus tried to use magnetism to cure diseases, but accomplished nothing. 

All its supposed successes were due to placebo effect. Even today we are also 

trying to sell magnetic bracelets and other devices as a remedy for many ailments, 

but there is no scientific evidence of its benefits

magnetic microwire

1. The Community of Madrid, through the Ministry of Education
2.  (Directorate General for Universities and Research), awarded
3.  this initiative in the First Contest of Ideas for Spin-Off of 
4. Researchers madri d in the area of New Materials, 
5. Nanotechnology and Technology Production, the project entitled 
6. "Project for the creation of a company dedicated to the manufacture,
7.  research, innovation, and commercialization of amorphous magnetic
8.  materials."In a first stage the work Micromag focused on automation 
9. and mass production of amorphous magnetic microwire. This objective
10.  has been achieved by modifying the laboratory equipment, making them 
11. more stable, and ensuring repeatability of the process. Incorporated, also, 
12. a system for quality control. These improvements have led to currently 
13. available production methods and efficient enough to be controlled to 
14. meet new applications.A magnetic microwire is a continuous filament of
15.  less than 100 mm in diameter consisting of a metallic core covered with a
16.  layer of glass. The manufacturing method, which depends directly on the 
17. cast in one operation, is inherently cheaper and has been used successfully
18.  to produce a wide range of metals and alloys that vary in size 100 ìm to 3 mm
19.  in diameter total. Amorphous magnetic microwires with exceptional magnetic
20.  properties are usually obtained using the technique of Taylor-Ulitowski. The 
21. core diameter and thickness of the cover are just microns.The interesting magneto
22. c properties of microwires are strongly correlated with its high axial magnetic 
23. anisotropy. This is because the amorphous structure, cylindrical geometry and 
24. mechanical stress generated during the manufacturing process due to the 
25. difference between the coefficients of thermal expansion of glass and metal.Among
26.  the many applications that can be used amorphous magnetic microwires stresses its
27.  use as a base for composite materials (composites), which have high absorption 
28. properties of high frequency electromagnetic radiation in the range of 0.5 to 25 GHz . Micromag has been able to integrate the microwire in different materials such as silicon, glass fibers, paints and construction materials, achieving levels of attenuation of the
29.  incident radiation very high.The magnetic sensors developed using microwaves are
30.  based on the operational principles strongly related to its composition and axial 
31. anisotropy through the magnetostriction constant and represented the effect of
32.  a large Barkhausen jump, and giant magnetoimpedance Mateucci effect.
33.