Presented by : Arvind Singh Heer MSc-I (Sem-II) Inorganic Chemistry MITHIBAI COLLEGE

MAGNETISM

CONTENT

INTRODUCTION

TYPES OF MAGNETISM

CURIE AND CURIE WEISS LAWS

MAGNECTIC SUSCEPTIBILITY

INTRODUCTION Magnetism is a property of

materials that respond to an applied magnetic field that cause the material to be either attracted or repelled.

TYPES OF MAGNETISMParamagnetic

Ferromagnetic

Antiferromagnetic

ferrimagnetic

DiamagneticFeebly repelled by the magnetic

fields. Non-metallic elements (excepts O2, S) inert gases and species with paired electrons are diamagnetic

All paired electrons

TiO2, V2O5,NaCl, C6H6(benzene)Insulator

Paramagnetic Attracted by the magnetic field due

to the presence of permanent magnetic dipoles (unpaired electrons). In magnetic field, these tend to orient themselves parallel to the direction of the field and thus, produce magnetism in the substances.

 At least one unpaired electron

O2, Cu2+, Fe3+, TiO, Ti2O3, VO, VO2, CuO

Electronic appliances

Ferromagnetic

Permanent magnetism even in the absence of magnetic field, Above a temperature called Curie temperature, there is no ferromagnetism.

 Dipoles are aligned in the same direction

Fe, Ni, Co, CrO2CrO2 is used in audio and video tapes

AntiferromagneticThis arises when the dipole

alignment is zero due to equal and opposite alignment.

 

MnO, MnO2,Mn2O, FeO, Fe2O3; NiO, Cr2O3, CoO, Co3O4,

CURIE LAW This law indicates that the susceptibility of

paramagnetic materials is inversely proportional to their temperature, i.e. that materials become more magnetic at lower temperatures. The mathematical expression is:

M- magnetisationX- magnetic susceptibilityH- magnetic fieldT- absolute temperatureC- curie’s constant

CURIE & WEISS LAW The temperature dependence of

which requires an amended version of Curie's law, known as the Curie–Weiss law:

θ - Weiss constant

MAGNETIC SUSCEPTIBILITYMagnetic susceptibility is related to

the force experienced by a substance in a magnetic field

The magnetic moment is calculated from the magnetic susceptibility, since the magnetic

moment is not measured directlyThe magnetic susceptibility per unit

volume is K = I/HI – magnetic inductionH – magnetic field

Generally, it is more convenient to use mass units,therefore the mass or gram susceptibility is defined as:

xg =k/dwhere d is the density of the solid.

The molar susceptibility is the mass susceptibility

multiplied by the formula weight.

xm= xg(F.W. in g mol ) -1

In the Faraday balance the field is inhomogeneous.

The pole pieces of the magnet are so shaped that there is region in which the product of the field strength and field gradient in the z direction is constant.

The sample is placed in this region. The force in this case is independent of the

packing of the sample and depends only on the total mass of the material present.

The method is sensitive and highly reproducible and can be applied to single crystals

The force is measured as a weight change, using a torsion balance.

Magnetic behavior may be distinguished by the values of χ and μ and by their temperature and field dependence

1. Positive vs. negative value: only diamagnetic materials show negative χ

2. Absolute value: ferromagnetic materials show huge positivevalue

3. Temerature dependence: diamagnetism is not temp. dependence,

antiferromagentic materials increase with increasing temp, and

para- and ferromagnetic materials decrease with increasing temp

4. Field dependence : only ferro- and antiferromagnetic materials show

field dependence

REFERENCEChemical Structure and Bonding H.B. Gray R.L. Dekock

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