many instances of heavy use in fields like rotating machines, loudspeakers, ferrite antennas, transformers and inductors have been ubiquitous. A material shows four different kinds of magnetic behavior and of them the main focus of our study are ferro- and ferri- magnetic properties. Apart from the twos we have paramagnetic and diamagnetic magnetic substances. the science of magnetism in todays world of modern sciences also encompass the special property of Superconductivity. superconductivity is the property of complete loss of magnetic behavior in a material. it finds use in many different domain of engineering and plays a very critical role there.
Superconductivity :- the property in itself is very interesting and finds use in many different fields of application. A seminal research done at IBM, a pioneer in computer engineering research, was successful in bring this special property at a higher temperature (Tc) of 77K.
application:- solenoids, sensitive magnetometers , and high Q-microwave filters
Exploring the magnetic properties in detail :::::- Sciences of magnetic properties..
Magnets:--All matter shows the mysterious properties of magnetism. A typical property of a magnet and magnetic field is magnet kept in inhomogeneous magnetic field either attracts it or repels it. and this very dogma is central to the magnetic properties of various material. A current or a moving charge produces magnetic field and electrons present within the atoms are responsible for the same. but why does it differ do they not contain same type of electrons and even if it has something to do with difference on atoms then we ought to observe the periodicity but we fail to do so.
magnetic dipole is defined as the product of ( current [ I ] [A] and directed perpend 2 the area of plain..)
the magnetic field is inversely proportional to r^3..
Now in details the ATOMIC magnetic moments:::
current= q/ T= -e*f=-e*w/2pi
1u = I * A= -ewr^2/2
1_u_orb=-e/2m_e L
1u_spin=-e/m_eS
L=mwr^2
the spin magnetic moment precess about the axis PRECESS
Precession is an interplay of torques and angular momentum .
a very important and striking phenomenon in the atomic substructure is that not all of the electrons are involved in the magnetic properties of the material. the inner orbital electrons cancel their L and S within the atom. and the magnetic phenomena is mainly shown by the valence electrons which are unpaired.
Sz= quantizes magnetic moment = ms*h/2pi
MAGNETISATION vector M :::::----
Bo=Uo*n*I [n * I = I' ]
M is actually a measure of the magnetization of the material medium. a meterial when put into a solenoid having a B of UoNI develops a magnetization M ( and this quantified property helps us to predict the overall magnetic field in the space);
in actuality M is magnetic moment per unit volume
here Nat is no of atoms / unit volume and Uav is the average magnetic dipole moment...
so by definition total magnetic moment = M A L
it can be shown from simple physics that :::::---
M A L = I_m L A
so M = I_m
this particular formula derived is general in nature and emphasised that this Im is not due to atomic motion but totally of localised electronic nature.
B = Uo( I' + Im)= Bo+ Uo*M
here I' is the current actually applied and Im is the induced one.
Magnetizing Field H = B/Uo
Ampere law relates the curl of B around the boundary with the current passing through the circuit ...
B/Uo = H relates the H curl over the surface directly with the current..
H* 2pi=I::::
the resulting B is combined of both the applied and the New magnetism in the material
Varioius formulas associated with B amperes laws and H and M are as follow:::::----
2> magnetic flux
3> magnetic dipole moment
4> bohr magneton B
5>Magnetisation Vector M
6> Magnetic Susceptibility Xm
7>absolute permeability Uo c=(Eo*Uo)^(1/2)
8> relative permeability Ur=B/UoH the change in u corresponding to the material medium
9> magnetic permeability the changed magnetic permeability
10> inductance L=Phi/I total flux threaded per unit current.
11> magnetostatic energy density Evol H d(B)
Amperes Law and the inductance of a toroidal coil ::::
integral of H over circular region =NI
H = NI/ l (l = perimeter)
B = U H = Uo Ur H
L = total flux threaded / current ::::::
the current has the property of threading magnetic flux in the circuit and that circuit works as Inductor by the grace of Lenz law:::
in a toroid we apply a magnetic field and then the innate relationship existing between the magnetic field and current through maxwells equations helps us to find the the H inside the toroid..
Hl=NI
Faradays law = d(total flux )/d(t) =Nd(phi)/d(t) = N A dB/dt
Energy density = integrating over of ( H * d(B))
B=ur uo * H
MAGnetostatic energy density ::::----- Evol=0.5*Ur*Uo*H^2
Evol (air) = 0.5 * Uo * H^2
Evol = 0.5* H * B
Magnetic Material classification ::::-
every magnetic property we are exploring right now is related with
the formula B = Bo+U*H
A>>>> Diamagnetisation :::--- typical diamagnetic with Xm = -5.2* 10^ -6
with the grace of lenz law we have
a diamagnetic material placed in a non-uniform magnetic field experiences force in lesser magnetic field ::
this repels the magnetic field>>>>>
basics what it happens in diamagnetic materials :::
Superconductors have Xm=-1 :::; perfectly diagmagnet ----
carbon copper plastic water
PARAmagnetic ___
they have positive Xm >0
and generally its not much as larger so we dont expect any significant difference>>
o2 is paramagnetic :::::
liquid nitrogen is attracted by the magnetic field
actually in Paramagnetic substances they do posses some permanent magnetisation but due to thermal agitation they tend to lose the magnetic property.
with the assistance of external magnetic field theres an increase in magnetism and is attracted towards the field.
examples of paramagnetic substances ...
platinum and aluminumi
generally metals because they have free valence electroncs outside their closed shell
Ferromagneti
sm :::---
materials::- iron
origin::- quantum mechanical exchange energy
magnetic domains
slowly with the application of magnetic field the M in the material saturates ::
Xm :::-- very high and +ve
CURIE temperature is the critical temperature below which the material shows ferromagnetism and above it it loses to paramagnetism ::
Anti - ferromagnetism
such as::--- chromimun
Xm= small but positive ::
origin :: quantum mechanical exchange forces
explantion:: magnetic moments allign in opposite direction and cancell one - another
in the absence of applied field no magnetisation
NEEL temperature Tn
above Tn antiferromagnetic material becomes paramagnetic :::
 |
| cromium BCC(r) unmagnetised |
Ferrimagnetic material :::
thers some magn even in absenc of B
such as::-- ferrites
origins:: unequal cancellation of magnetic field
Curie temperature effect applied here also ..
N.B. ferrimagnetic materials are generally not conducting so they generally donot suffer from eddy current losses:::
Either ferro or ferri are heavily used in applications involving magnets....
ORIGINS OF ferro and ferri magnetism :::- very important as these are d only substances used
its quantum mechanical in nature and depends on
a> Pauli Exclusion principle
b> electrostatic interaction energy
EXCHANGE interaction bhi bolte hain
ms and ml are so adjusted to minimize the energy of the system .....
an isolated Fe has four unpaired electrons
in modern theory of solids we came with the idea that the electrons does not belong to a particular atom but to the all...
Fe Ni Co Hunds rule of multicipality
for Fe it is 2.2 per atom
Josephson effect:::--
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