Magnetic susceptibility of magnetic materials

Magnetic Susceptibility of magnetic materials

1. Kingdom of Saudi Arabia Al-Imam Mohammad Ibn Saud Islamic University College of Sciences Department of Physics Title : Magnetic Susceptibility of magnetic materials Prepared by: Samia Abdullah A_lotaibi Supervisor: Dr. Mohamed Alamen 1 21/12/39 1

2. Introduction This final project will be dived in two parts : 1) first part : we will study each type of magnetic materials by giving the definition, magnetic susceptibility, the properties and some examples. Four type of magnetic materials are reviewed: diamagnetic, paramagnetic, ferromagnetic and anti-ferromagnetic. 2) second part : we will determine experimentally the type of some magnetic materials based on the magnetic susceptibility by using vibrator sample magnetometer (VSM) located at physics department –Al imam University. 2 21/12/39 2

3. * First part * 3 21/12/39 3

4. Magnetic Susceptibility Magnetic Susceptibility : is the ratio of the intensity of magnetism induced (M) in a substance to the magnetizing force or intensity of field (B) . Magnetic susceptibility reflects a material's degree of sensitivity to magnetic fields . , (CGS) * magnetic field intensity have two expression which are equally (B = H). * units of χ is dimensionless. Where : χ : is the magnetic susceptibility of material . M : is the Magnetization of material or the total magnetic moment per unit volume . B : is the magnetic field intensity (applied magnetic field). 4 21/12/39 4

5. Types of magnetic materials : 1) Diamagnetic 2) paramagnetic 3) ferromagnetic 4) anti-ferromagnetic 5 21/12/39 5

6. Diamagnetic Materials Diamagnetic substances are composed of atoms which have no net magnetic moments. A negative magnetization is produced when the material is exposed to external magnetic field, thus the susceptibility is negative . Figure 1. Relationship between temperature and magnetic susceptibility for diamagnetic materials 6 21/12/39 6

7. In diamagnetic materials, the magnetic susceptibility can be accurately predicted by Langevin's classical theory of electromagnetism as follows : Where : : frequently a susceptibility is defined referred to unit mass or to a mole of the substance , which means The molar susceptibility . : the magnetic permeability of a vacuum in H. Z : the atomic number of the atom . n : the atomic density in e : the elementary charge in C . : the root mean square of the square of the atomic radius in .   7 21/12/39 7

8. Properties of diamagnetic materials : Diamagnetic materials exhibit small and negative magnetic susceptibility in the range . Relative magnetic permeability of diamagnetic materials is always less than unity that is μr < 1 . Magnetic susceptibility of diamagnetic materials does not change with temperature   Examples of diamagnetic materials are : Gases such as hydrogen, nitrogen, chlorine, and bromine and noble gases such as He, Ne, Ar , Kr, Xe . The chemical elements from group IIA(2): Be; group IIIA(13): B, Ga , In, Tl ; group IVA(14): C, Si, Ge , Pb ; group VA(15): P, As, Sb , Bi, group VIA(16) S, Se, Te; group IA(11): Cu, Ag and Au; group IIA(12): Zn, Cd , Hg . Crystalline solid materials such as ( MgO ) and diamond . 8 21/12/39 8

9. Paramagnetic Materials In the paramagnetic materials, the magnetic moments do not interact with each other and they are randomly arranged in the absence of a magnetic field . Figure 3: Spin orientation in paramagnetic materials before and after applying magnetic field When a field is applied , the atomic magnetic moments are aligned in the direction of the field and that will induce a net positive magnetization and positive susceptibility . 9 21/12/39 9

10.   The efficiency of the field in aligning the moments is opposed by the randomizing effects of temperature. This results in a temperature dependent susceptibility, known as the Curie Law . Figure 4: Relationship between temperature and magnetic susceptibility for paramagnetic materials. 10 21/12/39 10

11. The temperature dependence of the magnetic susceptibility of paramagnetic materials is given by the Curie Law : Curie Law where: : it is the magnetic permeability of a vacuum in . n : it is the atomic density in m : it is the microscopic dipolar magnetic moment of an atom in A. k : it is the Boltzmann constant in J. T : it is the absolute thermodynamic temperature in K : the paramagnetic Curie temperature in K at which the susceptibility reaches its maximum value. C : it is the the paramagnetic Curie constant in 11 21/12/39 11

12. Properties of paramagnetic materials : 1) The magnetic lines of forces due to the applied field are attracted towards the paramagnetic material. 2) When placed in a non-uniform magnetic field, the paramagnetic materials move from weaker parts of the field to the stronger parts. 3) Permeability of paramagnetic material is greater than 1. 4) Magnetic susceptibility of paramagnetic material is positive 5) Susceptibility of paramagnetic materials varies inversely with the temperature ( Curie law ). 6) Arises from permanent dipole moments on the atoms. Examples of paramagnetic materials : Gases for example: oxygen , and all the chemical elements dealing with diamagnets for example :Li , Na , Mn , and all the platinum-group metals: Ru , Os, Pt. 12 21/12/39 12

13. Ferromagnetic Materials Ferromagnetic materials have magnetic dipolar moments aligned parallel to each other even without an external applied magnetic field. Figure 5 : Spin orientation in ferromagnetic materials 13 21/12/39 13

14. Curie temperature The Curie temperature is the temperature above it the ferromagnetic materials become paramagnetic . Figure 6 : Relationship between magnetic susceptibility and temperatures for ferromagnetic materials Materials Co Fe Ni Gd Fe2O3 MnAs Curie temperature(K) 1388 1043 627 292 948 318 * Examples of Curie temperature for some materials: 14 21/12/39 14

15. Properties of ferromagnetic materials : A ferromagnetic materials has a spontaneous magnetic moment- a magnetic moment even in zero applied magnetic field (at H = 0) below . 2) All ferromagnetic materials become paramagnetic above a temperature called Curie temperature T c . 3) Permeability is greater than 1 . 4) Magnetic susceptibility is large and positive . 5) Magnetic susceptibility decreases with the rise in temperature according to Curie law . 6) The source of ferromagnetism is the spin of the electrons . Examples of ferromagnetic materials : Nickel , cobalt, iron . 15 21/12/39 15

16. Anti-ferromagnetic materials In the antiferromagnetic materials, the alignment of the spin moments of neighboring atoms or ions in exactly opposite directions Figure 7: Spin orientation of anti-ferromagnetic materials 16 21/12/39 16

17. Neel temperature The Neel temperature is the temperature above it the anti-ferromagnetic materials become paramagnetic . Figure 8: Relationship between susceptibility and temperatures for antiferromagnetic materials Examples of Neel temperature for some materials: Materials Cr NiO FeO MnO CoO MnS Neel temperature(K) 308 525 198 116 291 160 17 21/12/39 17

18. Properties of antiferromagnetic materials : The antiferromagnetism will not produce any magnetisation because of the two opposing spin components . 2) When we applied external field , the net magnetization will be different of zero due to that the maximum spin are in the same direction . Antiferromagnetism is a special case of ferrimagnetism . Neel temperature is the critical temperature for the antiferromagnetic materials . Examples of antiferromagnetic materials : MnO , FeO, MnF2 . 18 21/12/39 18

19. * Second part * 19 21/12/39 19

20. Experimental results In this part, we studied the magnetic properties of three materials by using vibrator sample magnetometer (VSM) equipment located at physics department. An external magnetic field is applied on the powders materials and the magnetization values are registered . Based on the definition of magnetic susceptibility in the first part of this report, we will determine the type of each materials by calculating the value for each materials . 20 21/12/39 20

21. ZnO powder Fig.9 shows the magnetization of ZnO powders . If we compare this figure to Figure 1 in the first part of this report, we can conclude that the behavior is similar to diamagnetic materials . Figure 9. : Magnetization of ZnO powder 21 21/12/39 21

22. We can confirm this conclusion by calculating also the magnetic susceptibility for this materials . The magnetic susceptibility is :   If we take : ( x , y ) = ( m ,B ) , where : m = Magnetic Field (G) , B = Moment (emu)   magnetic susceptibility for two points :   So we conclude from the calculation of the magnetic susceptibility of the Zno materials which are negative that ZnO is diamagnetic materials . 22 21/12/39 22

23. ZnO:Mn powder We showed in Fig.9 that ZnO is diamagnetic materials. If we doped it with ferromagnetic materials, we are expecting that this magnetic behavior changes . Fig.10 shows the magnetization of ZnO doped with 5% of Mn . It can be seen that ZnO change behavior comparing to Fig.9 . If we compare Fig.10 to Fig.4 of the first part, we can conclude that (ZnO:Mn) is a paramagnetic material . Figure 10. : Magnetization of ZnO doped Mn powder 23 21/12/39 23

24. From the data table the magnetic susceptibility :   If we take : ( x , y ) = ( m ,B ) , where : m = Magnetic Field (G) , B = Moment (emu)  magnetic susceptibility for two points :   We conclude from the figure and from the positive value of the magnetic susceptibility that ZnO:Mn powder is paramagnetic material . 24 21/12/39 24

25. Ni powder Fig.11 shows the magnetization of Ni powders. It is clear that the behavior is different from the previous materials ( ZnO and ZnO:Mn ) . Figure 11. : Magnetization of Ni 25 21/12/39 25

26. From the data table the magnetic susceptibility :   If we take : ( x , y ) = ( m ,B ) , where : m = Magnetic Field (G) , B = Moment (emu) magnetic susceptibility for two points : So we conclude from the calculation the magnetic susceptibility of the Ni powder which is a positive and high that Ni materials is ferromagnetic materials. 26 21/12/39 26