Types of magnetic materials

Magnetic materials can be classified in terms of the arrangements of magnetic dipoles in the solid. These dipoles can be thought of, a little imprecisely, as microscopic bar magnets attached to the various atoms present. Materials with no elementary magnetic dipoles at all are diamagnetic. 

The partial orientation of the elementary dipoles in a paramagnetic solid is counteracted by thermal agitation, and it would be expected that at high temperatures 

Above a temperature called the Curie temperature, Tc, all ferromagnetic materials become paramagnetic. The transition to a paramagnetic state comes about when thermal energy is greater than the magnetic interactions and causes the dipoles 

The Curie-Weiss constant, 0, is positive, has the dimensions of temperature, and a value usually close to, but not quite identical to, the Curie temperature, TC- The transition is reversible, and on cooling, ferromagnetism returns when the magnetic dipoles align parallel to one another as the temperature drops through the Curie temperature. 

Magnetic materials can be classified in terms of the arrangements of magnetic dipoles in the solid. 

These dipoles can be thought of, a little imprecisely, as microscopic bar magnets attached to the various atoms present. 

Paramagnetic solids are those in which some of the atoms, ions or molecules making up the solid possess a permanent magnetic dipole moment. These dipoles are isolated from one another. The 

Interacting magnetic dipoles can produce a variety of magnetic properties in a solid. The 

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There is considerable interest in developing new types of magnetic materials, with a particular hope that ferroelectric solids and polymers can be constructed— materials having spontaneous electric polarization that can be reversed by an electric field. Such materials could lead to new low-cost memory devices for computers. The fine control of dispersed magnetic nanostructures will take the storage and tunability of magnetic media to new levels, and novel tunneling microscopy approaches allow measurement of microscopic hysteresis effects in iron nanowires. 

Under the size reduction of small magnetic particle a critical volume exists when the energy to produce a domain wall becomes higher than the external magnetostatic energy for the single-domain state. This critical size depends on type of magnetic material and is about few tens nanometers. For a spherical particle, this critical diameter could be estimated as [1] ... 

Which type of magnetic material cannot be used to make permanent magnets, a ferromagnetic substance, an antiferromagnetic substance, or a ferrimagnetic substance ... 

There are many different types of magnetic material and they all respond differently to being magnetized. Some materials magnetize easily, and some are difficult to magnetize. Some materials retain their magnetism, while others lose it. The result will look like the graphs shown in Fig. 2.44 and are called hysteresis loops. 

In this chapter, using samples of mainly three types of magnetic materials, namely, nanosized powders of ferrites, mechanically alloyed/milled Fe-Cr-AI intermetallics, and a Fe-AI multilayer system, it has been demonstrated how Mossbauer spectroscopy is a powerful tool to understand the bulk magnetic properties in such nanosized systems. This is mainly because of the extreme sensitivity of the Mossbauer probe atom to short-range effects that get modified on a... 

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