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MAGNETIC PROPERTIES AND PARAMAGNETISMSubmitted ByNavaneeth Krishnan A R B130592CHNaven Kalirana B130660CHNeethu Sreedhar B130757CH

MagnetismMagnetism is a phenomenon by which materials assert an interactive or repulsive force or influence on other materialsMagnetic properties of a solid originate due to the motion of electrons inside them, and their magnetic moments or dipoles The magnetic field can be described by imaginary lines as for a magnet and a current loop.Magnetic Field Representation

Magnetic lines of forceMagnetic MomentsBeing a moving charge, electrons produce a small magnetic field having a magnetic moment along the axis of rotation.The spin of electrons also produces a magnetic moment along the spin axis.Magnetism in a material arises due to alignment of magnetic moments.

Magnetic DipolesAnalogous to electric dipole, a magnetic dipole can bedefined as two monopoles of opposite and equal strength separated by a certain distance.A magnetic monopole, however, is not observed in nature.Two monopoles of strength +m andm separated bydistance l,will give a dipole = m1 m2 = m(1 2) = mA bar magnet can be thought of consisting of two opposite and equal poles at its two ends.

6TerminologiesMagnetic field StrengthIf a magnetic field, H, is generated by a cylindrical coil(solenoid) of n turns and length l, H = nI/l (A/m) Magnetic flux density, B: It is the magnitude of the fieldstrength within a substance subjected to a field HB = H (Tesla or Weber/m2), called the permeability, is the measure of the degree towhich a material can be magnetized.In vacuum B = oH. o is the permeability of vacuum and is auniversal constant o = 4x 10-7(H/m).r =/o is the

MagnetizationWith the application of a magnetic field magnetic moments in a material tend to align and thus increase the magnitude of the field strength.This increase is given by the parameter called magnetization,M, such that B = oH + oM.M = mH.m is called magnetic susceptibility. m=r 1

Types of Magnetic MaterialsDepending on the existence and alignment of magneticmoments with or without application of magneticfield,magnetic materials can be classified as: Diamagnetic materialsParamagnetic materials Ferromagnetic materialsAnti Ferromagnetic materialsFerrimagnetic materials

Orientation of magnetic moments

IIn(a) the permanent dipoles are absent,therefore they cannot be made magnets(Diamagnetic materials)

In(b)the permanent moments are randomly oriented.they align themselves parallel to the applied field feebly and become weak magnets(paramagnetic materials)

In (c) a ferromagnetic material in which magnetic moments are alligned and are equal in magnitude are shown

In (d) antiferromagnetic material in which magnetic moments are alligned whichare equal in magnitude opposite in direction are shown

In (e) ferrimagneticmaterial in which magnetic moments are alligned are unequal in magnitude and in opposite directions are shown Paramagnetic Materials In a paramagnetic material the cancellation of magnetic moments between electron pairs is incomplete and hence magnetic moments exist without any external magnetic field.

However, the magnetic moments are randomly aligned and hence no net magnetization without any external field.

When a magnetic field is applied all the dipole moments are aligned in the direction of the field.This results in feeble magnetization and is reffered as paramagnetization

Examples : Oxides of Al,Zn,Cr,Ti,Mo and Rare earth based compounds such as EuS,ErNi2

The magnetic susceptibility is small but positive. i.e. B in a paramagnetic material is slightly greater than that of vacuum.B versus H curve of a Paramagnetic Material

16By analysing the curve we undestood that both the flux density B within them is almost the same as it would be in a vaccum.

Both diamagnetic and paramagnetic are considered to be nonmagnetic,they exhibit magnetization in the presence of an external fieldCuries LawFor low levels of magnetization,paramagnets follow Curies Law.The law indicates that the susceptibility of paramagnetic material is inversely proportional to their temperature ie, the material becomes more magnetic at lower temperature

M = H=(C/T)HM is resulting magnetization , is magnetic susceptibility,H is auxillary magnetic field, Tis abs. temp, C is material specific curie constant.This law is not applicable under high field/low temperature regime where saturation magnetization occurs and magnetic dipoles are all arranged with the applied fields.

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