Magnetism

A complete Detail on Magnetism which gives a broad idea about the topic

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

2. CONTENT INTRODUCTION TYPES OF MAGNETISM CURIE AND CURIE WEISS LAWS MAGNECTIC SUSCEPTIBILITY

3. INTRODUCTION Magnetism is a property of materials that respond to an applied magnetic field that cause the material to be either attracted or repelled.

4. TYPES OF MAGNETISM Paramagnetic Ferromagnetic Antiferromagnetic ferrimagnetic

5. Diamagnetic Feebly repelled by the magnetic fields. Non-metallic elements (excepts O 2 , S) inert gases and species with paired electrons are diamagnetic All paired electrons TiO 2 , V 2 O 5 ,NaCl, C 6 H 6 (benzene) Insulator

6. 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 O 2 , Cu 2+ , Fe 3+ , TiO , Ti 2 O 3 , VO, VO 2 , CuO Electronic appliances

7. 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, CrO 2 CrO 2  is used in audio and video tapes

8. Antiferromagnetic This arises when the dipole alignment is zero due to equal and opposite alignment.   MnO , MnO 2 ,Mn 2 O, FeO , Fe 2 O 3 ;  NiO , Cr 2 O 3 ,  CoO , Co 3 O 4 ,

9. 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- magnetisation X - magnetic susceptibility H- magnetic field T- absolute temperature C- curie’s constant

10. 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

11. MAGNETIC SUSCEPTIBILITY Magnetic 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 directly The magnetic susceptibility per unit volume is K = I/H I – magnetic induction H – magnetic field

12. Generally, it is more convenient to use mass units,therefore the mass or gram susceptibility is defined as: x g = k /d where d is the density of the solid . The molar susceptibility is the mass susceptibility multiplied by the formula weight. x m = x g (F.W. in g mol ) -1

13. 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 .

14. 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

15. REFERENCE Chemical Structure and Bonding H.B. Gray R.L. Dekock - THANK YOU