Fundamental Physics Concepts: Magnetism

(a)Ferromagnetic materials:
Ferromagnetic materials have a large, positive susceptibility to an external magnetic field. They exhibit a strong attraction to magnetic fields and are able to retain their magnetic properties after the external field has been removed. Ferromagnetic materials have some unpaired electrons so their atoms have a net magnetic moment. They get their strong magnetic properties due to the presence of magnetic domains. In these domains, large numbers of atom's moments (1012 to 1015) are aligned parallel so that the magnetic force within the domain is strong. When a ferromagnetic material is in the unmagnitized state, the domains are nearly randomly organized and the net magnetic field for the part as a whole is zero. When a magnetizing force is applied, the domains become aligned to produce a strong magnetic field within the part. Iron, nickel, and cobalt are examples of ferromagnetic materials. Components with these materials are commonly inspected using the magnetic particle method.
All ferromagnetic materials have a maximum temperature where the ferromagnetic property disappears as a result of thermal agitation. This temperature is called curie temperature.
To determine curie temperature by varying the voltage across the kanthal wire

ABSTRACT :
This report is based upon the experiment in which “curie temperature of kanthal wire’’ was measured. by the variation of voltage connected across it. We know that the wires become hot due to passage of current through them This is due to the fact that when an external source is connected across the ends of a wire it exerts a force on the atoms due to which the atoms start vibrating and collide with each other as the voltage increases the no. of collisions increases due to which the temperature increases .Using this phenomena kanthal wire was chosen because it has a very high resistance and gets red hot in a small amount of time. Condition of kanthal wire was observed after regular intervals for different values of voltage (V) and current (I). A graph was plotted between voltage and current to verify their direct relationship. The curie temperature was measured with the help of formula .

Theoretical review:
Classification on the basis of Magnetism:
Materials can be classified on different basis. We are going to classify them on the basis of magnetic properties. Some of the materials show response to the applied magnetic fields while others don’t show any response. This is because each atom of any material has its own magnetic moment which arises due to spin of electrons. The macroscopic magnetic behavior of any material arise from the magnetic moments of its component atoms. The classification of materials on the basis of magnetism is as follows:
Paramagnetic Materials:
These materials are weakly attracted when magnetic field is applied on them. The electrons of their constituent atoms are aligned in such a way that they do not cancel out each other’s magnetic moments and there exists a resultant magnetic moment, however small it may be. The example of paramagnetic materials is Oxygen.

Diamagnetic materials:
These materials experience weak repulsive forces when acted upon by magnetic fields. This is because there are equal number of electrons spinning in opposite directions and they cancels out each other’s magnetic moment.
Ferromagnetic materials:
These materials show very strong magnetic behavior when magnetic field is applied. Actually their atomic magnets or dipoles do not act independently but many of the atoms having same magnetic moments form groups and they are collectively called Domains. In demagnetized state, all the domains have magnetic moments point in arbitrarily random direction and the ferromagnetic material as a whole is neutral. But when this material is put in the magnetic field all the domains in it align themselves in the direction of applied magnetic field. When the magnetic field is removed, the domains in some of the ferromagnetic materials get random again instantly but there are some ferromagnetic materials which keep their domains aligned in the direction of applied magnetic field even after the removal of the magnetic field. Those materials are also used for making permanent magnets.
Ferromagnetism and Concept of Domains:
The ferromagnetic materials are much more stronger in their magnetic character because there are different alignment of their constituent atoms. Their atoms do not respond independently on application of magnetic field but they form groups of atoms having equal and unidirectional magnetic moments. These small groups are called domains. Each domain has all of its atoms pointing in the same direction and they form a strong resultant magnetic moment. In the demagnetized state when there is no magnetic field applied then all the domains have random directions and the whole material is neutral macroscopically. But when the material is put in the magnetic field then all the domains line up in the direction of the applied magnetic field and the entire specimen becomes saturated. On the removal of magnetic field some of the ferromagnetic materials lost saturation just after the removal like Iron. But there are some materials which retain this saturation even after the removal of magnetic field. These are called strong magnetic materials. Steel is one of them and used for making permanent magnents.
But all this happens below a certain temperature which is different for different materials. When that temperature is attained, the ferromagnetic material loses its saturation and become paramagnetic. That temperature is called Curie temperature.
Curie temperature:
“The temperature at which a substance changes it’s “magnetic behavior” is called curie temperature”.
The Curie temperature is the critical temperature beyond which a previously ferromagnetic material becomes paramagnetic. On the atomic level, below the Curie temperature the magnetic moments, contributed by the electrons, are aligned in their respective domains and even a weak external field results in a net magnetization. As the temperature increases to curie temperature and above however, fluctuations due to the increase in thermal energy destroy that alignment .
Kanthal wire:
Kanthal is an iron-chromium-aluminium alloy (FeCrAl) . Kanthal wire is widely used in conditions where high temperature and resistance needs are to be fulfilled due to it’s property of high resistance. Kanthal (FeCrAl) alloy consist of mainly iron, chromium (20–30%) and aluminium (4–7.5 %). Kanthal FeCrAl alloy was developed by Hans von Kantzow in Hallstahammar, Sweden. Its name is derived from Kantzow and Hallstahammar. The alloys are known for their ability to withstand high temperatures and having intermediate electric resistance. As such, it is frequently used in heating elements AB.