CHAPTER 1 INTRODUCTION TO MAGNETIC MATERIALS

Transcription

1 1 CHAPTER 1 INTRODUCTION TO MAGNETIC MATERIALS 1.1 GENERAL The magnetic moment in a material originates from the orbital motion and spinning motion of electrons in an atom. so each atom represents a tiny permanent magnet in its own right. The circulating electron produces its own orbital magnetic moment, measured in Bohr magnetons (µb), and there is also a spin magnetic moment associated with it due to the electron spinning itself like the earth, on its own axis. In an atom generally every two electrons will form a pair such that they have opposite spins with the resultant spin magnetic moment zero. But in magnetic materials like iron, cobolt, nickel etc, there are unpaired electrons in 3d orbital. This unpaired electron spin magnetic moment interacts with that of adjacent atom and align in a parallel manner resulting in enormous spin magnetic moment. Hence these unpaired electron spins are responsible for magnetic behavior of materials. The value of spin magnetic moment is very large when we compare it with orbital magnetic moment. All materials can be classified in terms of their magnetic behavior falling into one of five categories depending on their bulk magnetic susceptibility. Magnetic susceptibility measures the degree of magnetization of a material in response to an applied magnetic field. It is positive for ferromagnetic and paramagnetic material and negative for a diamagnetic material. The most common types of magnetism are diamagnetism and

2 2 paramagnetism, which account for the magnetic properties of most the elements at room temperature (Decker 1995). They usually referred to as nonmagnetic, whereas those which are referred to as magnetic are actually classified as ferromagnetic. The only other type of magnetism observed in pure elements at room temperature is antiferromagnetism. Magnetic materials can also be classified as ferrimagnetic although this is not observed in any pure elements but can only be found in compounds, such as the mixed oxides, known as ferrites, from which ferrimagnetism derives its name. 1.2 CLASSIFICATION OF MAGNETIC MATERIALS On the basis of magnetic properties, different materials are classified into the following types Diamagnetism In a diamagnetic material the atoms have no net magnetic moment when there is no applied field. Under the influence of an applied magnetic field (H) the spinning electrons precess and this motion, which is a type of electric current, produces a magnetization (M) in the opposite direction to that of the applied field. The value of susceptibility is always negative and independent of temperature Paramagnetism In paramagnetic materials each atom has a magnetic moment which is randomly oriented as a result of thermal agitation. Application of a magnetic field creates the alignment of these magnetic moments to a better extent and hence a low magnetization in the same direction as the applied field is observed. As the temperature increases, the thermal agitation will increase and it will become harder to align the atomic magnetic moments and hence the susceptibility will decrease. The magnetic susceptibility is positive and low.

3 Ferromagnetism Ferromagnetism is possible when atoms are arranged in such a way that the atomic magnetic moments can interact to align parallel to each other. This effect is explained by the presence of an internal field within the ferromagnetic material. This field is sufficient to magnetize the material to saturation. The Heisenberg model of ferromagnetism describes the parallel alignment of magnetic moments in terms of an exchange interaction between neighboring moments. Weiss postulated the presence of magnetic domains within the material, which are regions where the atomic magnetic moments are aligned. The movement of these domains determines how the material responds to an external magnetic field and as a consequence, the susceptiblity becomes a function of applied magnetic field. The ferromagnetic materials are usually compared in terms of saturation magnetization (magnetization when all domains are aligned) rather than susceptibility. In the periodic table of elements only Fe, Co and Ni are ferromagnetic at and above room temperature. When heated the thermal agitation of the atoms lead to the misalignment of the atomic magnetic moments and hence the saturation magnetization decreases. If the thermal agitation is high the material becomes paramagnetic, the temperature of this transition is called Curie temperature, T C (Fe: T C = 770 C, Co: T C = 1131 C and Ni: T C = 358 C). The magnetic susceptibility for ferromagnetic material is positive and high Antiferromagnetism Antiferromagnetic materials are very similar to ferromagnetic materials but the exchange interaction between neighboring atoms leads to the anti-parallel alignment of the atomic magnetic moments. Therefore, the magnetic field cancels out and the material appears to behave in the same way

4 4 as a paramagnetic material. Like ferromagnetic materials these materials become paramagnetic above a transition temperature, known as the Neel temperature T N. The only element exhibiting antiferromagnetism at room temperature is chromium (Cr: T N = 37ºC). The susceptibility is very small and is positive Ferrimagnetism A material is ferrimagnetic if they are arranged into two groups with opposite magnetic moment alignments but one group involves atoms with a greater magnetic moment than the other. If we apply a small value of magnetic field, it will produce a large value of magnetization. The susceptibility is very large and is positive. Ferrimagnetic materials are also known as Ferrites. 1.3 FERRITES Generally mixed metal oxides with Fe 3+ ion as their main component are known as ferrites. Ferrites crystallize in three different crystal types, namely, Spinel (cubic), Garnet (cubic) and Hexaferrite (Hexagonal) (Smit and Wijn 1959; Viswanathan and Murthy 1990) Spinel The spinel structure takes its name from the mineral MgAl 2 O 4, which crystallizes in the cubic system. The general chemical formula for cubic spinel is AB 2 O 4 where A is the substitute for divalent metal ions like Mn 2+, Mg 2+, Ni 2+, Zn 2+, Co 2+ and Cd 2+ and B is the trivalent metal ions like Fe 3+. The oxide anions are arranged in a cubic close-packed lattice and the cations A and B occupy some or all of the octahedral and tetrahedral sites in the lattice.

5 Garnet Garnets have a cubic structure with a general chemical formula of A 3 B 2 Si 3 O 12 where A is the divalent cation like Mg 2+, Fe 2+ and Mn 2+, B is the substitute for trivalent metal ions like Al 3+, Cr 3+ and Fe Hexaferrite Hexaferrites have hexagonal structure with a general chemical formula of AFe 12 O 19 ; A can be Ba 2+ or Sr 2+. The hexagonal ferrite lattice is simillar to the spinel structure, with the oxygen ions closely packed, but some layers include metal ions, which have practically the same ionic radii as the oxygen ions. The lattice has three differernt sites occupied by metals. 1.4 SPINEL STRUCTURE The unit cell of the spinel has eight formula units (8 x AB 2 O 4 ). The 32 oxygen ions form a face centered cubic (FCC) lattice in which two kinds of intersitial sites are present, namely tetrahedral sites (A sites) and octahedral sites (B sites). There are 64 A sites and 32 B sites, of which only 8 and 16 respectively are occupied by metal ions. The crystal structure of spinel ferrite is shown in Figure 1.1 and is best described by subdividing the unit cell into eight octant with edge a/2 where a is the edge of the unit cell. The location of oxygen ions and metals ions in every octant can then be easily described. The oxygen ions are arranged in identical manner in all octants. Each octant contains four oxygen ions on the body diagonals and they lie at the corners of a tetrahedron. Each oxygen ion is located at a distance equal to one fourth of the length of the body diagonal from alternate corners of the octant. The array of oxygen ions as a whole in the crystal constitute a fcc lattice with edge = a/2 and thus, there are four such interpenetrating fcc oxygen lattice (Smit and Wijn 1959; Jan Smit 1971).

6 6 Figure 1.1 Structure of SPINEL (AB 2 O 4 ) The positions of metal ions are different in the two octants sharing a face. In one of the octants, an occupied tetrahedral site is located at the centre and four more sites on the corners of the octants. In the adjacent octant, the central site is not occupied, but owing translation symmetry, half of the corner sites are occupied. Thus, the occupied tetrahedral sites form two interpenetrating fcc lattice, having an edge a, which are displaced with respect to each other over a distance a 4 3 in the direction of the body diagonal of the cube. The unit cell parameter of some simple spinel ferrites are given in Table 1.1 (Alex Goldman 2006).

7 7 Table 1.1 The unit cell parameter of some simple ferrites S.No Ferrite Unit Cell Length (Å) 1. MnFe 2 O ZnFe 2 O FeFe 2 O CoFe 2 O NiFe 2 O Oxygen Parameter The interstices available in an ideal close packed structure of rigid oxygen anions can incorporate in the tetrahedral sites, only metal ion with a radius r tetra less than 0.30 Å and in octahedral sites only ions with a radius r oct less than 0.55 Å. In order to accommodate cations like Mn 2+, Ni 2+, Cd 2+, Co 2+, Mg 2+, and Zn 2+ the lattice has to be expanded. The ionic radii of the cations are given in the Table 1.2. (Shannon 1976). The tetrahedral sites are often too small for the metal ions so that the oxygen ions move slightly to accommodate them. The oxygen ions connected with the octahedral sites move in such a way as to shrink the size of the octahedral cell by the same amount as the tetrahedral site expands. The movement of the tetrahedral oxygen is reflected in a quantity called the oxygen parameter (u) which is the distance between the oxygen ion and the face of the cube edge along the cube diagonal of the spinel subcell. This distance is theoretically equal to 3 a. 8 However, the incorporation of divalent metal ion in tetrahedral sites induces a larger expansion of the tetrahedral site, leading to larger value of u than the ideal value (Smit and Wijn 1959).

8 8 Table 1.2 The ionic radii of cations S.No Ion Coordination Ionic Radius (Å) 1. Mn Fe 2+ Fe Ni 2+ IV High Spin VI Low Spin VI High Spin VI Low Spin VI High Spin IV High Spin VI Low Spin VI High Spin IV Low Spin 0.55 VI High Spin Cd 2+ IV 0.78 VI Co 2+ IV High Spin VI High Spin Zn 2+ IV 0.6 VI 0.74

9 Normal Spinel and Inverse Spinel The interesting and useful electrical and magnetic properties of the spinel ferrites are governed by the distribution of the iron and the divalent metal ions among the octahedral and tetrahedral sites of the spinel lattice. A whole range of possible distribution is observed and this can be represented in general terms by A 2+ B [A B ]O 4, where the ions inside the brackets are located in octahedral sites and the ions outside the brackets in tetrahedral sites. The limiting case, = 1 is called normal spinel and the other limiting case, when = 0 is called inverse spinel. For a random distribution = 1/3, which is also known as mixed ferrites Site Preference and Cation Distribution Chemical and physical properties of the ferrites depend on the distribution of cations in tetrahedral (A) and octahedral (B) sites. Zn 2+ and Cd 2+ show a marked preference for tetrahedral sites where their 4s, 4p, or 5s, 5p electrons respectively can form covalent bonds with the 2p electrons of the oxygen ion. Ni 2+ has a tendency to occupy octahedral sites due to the favorable charge distribution in an octahedral crystal field. Mn 2+ and Fe 3+ ions show preference for both A site and B site. In order to explain the site preference of transition metal ions in oxides, two theories namely crystal field theory and simplified molecular orbital theory have been proposed. Crystal field theory (Dunitz and Orgel 1957; McClure 1957) is based on ionic type of bonding, where as simplified molecular orbital (Blasse 1964) theory takes into account, the covalent bonding between oxygen and transition metal atoms. Experimentally the cation distribution can be studied by X-ray diffraction, Neutron diffraction and Mossbauer spectroscopy (Smit and Wijn

10 ; Jan Smit 1971; Kurt and Wills 1999; Verwey et al 1947; Trestman et al 1983). Most of the work on crystal chemistry of spinels is currently being carried out by X-ray diffraction measurements combined with the appropriate calculation methods. Among these are R-factor method, Furuhashi method and Bertaut method (Furuhashi et al 1973; Qiang-Min Wei et al 2001) are commonly used. The R-factor method, Furuhashi method and Bertaut methods are all based on comparison between the diffraction intensities observed experimentally and those calculated for large number of hypothetical crystal structure which is generated to cover a suitable range of cation distribution and u-parameter (Furuhashi et al 1973). The criterion used for such a comparison is the most distinctive feature of each method which is given below. R-Factor method also called as residual function method is a measure of the agreement between the calculated and the observed values of the intensities. In other words it is a measure of how well the calculated intensity fits the observed intensity data. R value less than 0.25 gives the correctness. Several expression of the residual function R are proposed, two of these are, hkl Iobs Ical R 1 (1.1) hkl Iobs hkl Iobs Ical R 2 (1.2) hkl Iobs This method enables simultaneous determination of cation distribution and oxygen parameter. Different models for the determination of

11 11 cation distribution and the u parameter are selected and used to get that calculated structure when the values of R1 and R2 factors are as low as possible. Furuhashi method is based on the fact that if the structure assumed for the intensity calculation of diffraction lines is exactly the same as the observed intensity of the sample, the linear relation between ln sin 2 2 must be found, according to equation. 2 2 hkl hkl ln k eff sin I I hkl hkl and ln I I 2B (1.3) where k is the scale factor, B eff is the effective temperature coefficient, I obs the observed intensity and I cal the calculated intensity for the diffraction line hkl and the diffraction angle of the line hkl. Bertaut method selects a few pair of reflections. Their relationships are given by equation I / I I / I (1.4) abs hkl abs h 'k 'l' calc hkl calc h 'k'l' where I and I calc are the observed and calculated intensities for reflection abs hkl hkl hkl respectively. An agreement factor R is defined by equation R I / I I / I (1.5) abs hkl abs h 'k'l' calc hkl calc h 'k'l' The closest match with the actual sample structure, obtained by varying the cation distribution in the calculated intensity, will produce a minimum for R. The corresponding cation distribution may be obtained for each hkl, h'k'l' reflection pair considered.

12 MAGNETIC INTERACTION IN FERRITES Three kinds of magnetic interactions are possible, between the metallic ions at A and B sites, through the intermediate O 2- ions, by superexchange mechanism, namely, A-A interactions B-B interaction and A-B interaction (Smit and Wijn 1959; Willard et al 1999; Standley 1972). The strength of interactions between moments on the various sites depends on the distances between these ions and the oxygen ion that links them and also on the angle between the three ions. The interaction is greatest for an angle of 180 with shortest interatomic distances. Figure 1.2 shows the interatomic distances and the angle between the ions for the different types of interactions. For the case of A-A and B-B interactions, the angles are too small or the distance between the metal ions and the oxygen ions are too large. For the case of AA interaction the angle is about 80, for B-B interaction, B-O-B angles are 90 and 125 and one of the B-O distances is large. The best combination of distances and angles are found in the A-B interactions. For an undistorted spinel, A-O-A angle is about 125 and 154. Therefore, the interaction between moments on A and B site is strongest. The BB interaction is much weaker and the most unfavorable interaction occurs between AA. Figure 1.2 Magnetic interaction in ferrites

13 13 As the AB interaction predominate, the spins of the A and B site ions in ferrites will be opposite with a resultant magnetic moment equal to the difference between those of A and B site ions. In general the value of saturation magnetic moment for the B sublattice (M B ) is greater than that of the A sublattice (M A ), so that, the resultant saturation magnetization (M s ) may be written as M s = M B - M A (1.6) Based on this, one can explain the experimentally observed magnetic susceptibility and magnetic saturation data obtained for ferrites Temperature Dependence of Magnetization in Ferrites The factors responsible for the variation of magnetization with temperature are the following: a) The magnitude of sublattice magnetizations at 0 K. b) The ratios of the magnitudes of exchange interactions between sublattices (i.e. AA, BB and AB). The dependence of M A and M B on temperature is usually complex. This is because the A site ions are situated in a strong internal field provided by the B site ions (each A site ion has 12 nearest neighbor B site ions) and the B site ions find themselves in a weak field provided by A site ions (each B site ion has only 6 nearest neighbor A site ions). Hence change of temperature causes different changes in the individual magnetizations. In general, magnetization due to A sublattice is not much affected by temperature, and decreases slowly, and drops to zero sharply at the Curie point, whereas B sublattice magnetization curve will pass through a minimum. Such a magnetization curve is known as type N. When M B is resistant towards

14 14 increase of temperature, a curve with a maximum will be observed and this curve is called type P. All simple ferrites are known to show fairly normal M s vs T variation (Pauthenet 1950). In some cases like CuFe 2 O 4 and MgFe 2 O 4, the magnetization temperature curves show strong dependence on the distribution of divalent cations in A site and B site. Ferrites exhibit hysteresis phenomena during the magnetization cycle. The shape of the loops varies, with respect to individual ferrites. For example Mg-Mn ferrites, Mn-Zn ferrites, Cu-Mn ferrites exhibit square hysteresis loops and such ferrites are used as memory core ferrites Magnetic Anisotropy In principle a magnetic material can be magnetized in any direction. In certain directions the magnetization process is easier, i.e., it requires only a very small field. This dependence of magnetization on the direction of magnetization is known as magnetic anisotropy. The value of magnetization energy required to turn the magnetization from the preferred direction to the desired direction is known as the anisotropy energy. 1.6 ELECTRICAL PROPERTIES OF SPINEL FERRITES Spinel ferrites score over the conventional magnetic materials in their application in one respect, that their electrical conductivity is low when compared to those of the other magnetic materials. This factor is responsible for the wide use of ferrites at microwave frequencies. While studying the electrical properties of ferrites one has to keep in mind that the properties are affected by the distribution of cations in the sites, by non-magnetic and magnetic substitutions, by the amount of Fe 2+ present, sintering conditions, grain size and grain growth effects. The values of resistivity of various ferrites

15 15 at room temperature vary on a wide range. The resistivity of ferrites shows an exponential dependence on temperature. Spinel ferrites, in general are semiconductors with their conductivity values varying between 10 2 and ohm -1.cm -1. The conductivity is due to the presence of Fe 2+ and Me 3+ (Me = Ni and Co) ions. The presence of Fe 2+ results in n-type behavior and of Me 3+ in p-type behavior. The conductivity arises due to the mobility of the extra electron (from Fe 2+ ) or the positive hole (Me 3+ ) through the crystal lattice. The movement is described by a hopping mechanism, in which the charge carriers jump from one ionic site to the next Conduction Mechanisms The increasing demand for low loss ferrites resulted in detailed investigations on the various aspects of conductivity and on the influence of various cationic substitution. The conduction mechanism in ferrites is quite different from semiconductors. The temperature dependence of mobility affects the conductivity and the carrier concentration is almost unaffected by temperature variations. In semiconductors the band type conduction occurs, whereas in ferrites, the cations are surrounded by closly packed oxygen anions and can well be treated as isolated from each other. There will be a little direct overlap of the anion charge clouds or orbital. In other words the electron associated with particular ion will largely remain isolated and hence a localized electron model is more appropriate than a collective band model. This accounts for the insulating nature of ferrites. An appreciable conductivity in these ferrites is found to be due to the presence of iron with different valence states at crystallographically different equivalent lattice points. Conduction is due to exchange of 3d electrons, localized at the metal ions, from Fe 3+ to Fe 2+. These factors led to the hopping electron model. Many

16 16 models have been suggested to account for the electrical properties, of which hopping model and small poloron model are significant Hopping Model of Electrons Jonker (1959) has observed in cobalt ferrites that the transport properties differ considerably from those of normal semiconductors, as the charge carriers are not free to move through the crystal lattice but jump from ion to ion. It is suggested that in materials like ferrites there is a possibility of exchanging the valence of a considerable fraction of metal ions and especially that of iron ions. In the presence of lattice vibration however the ions occasionally come close together for transfer to occur with a high degree of probability. Thus only the lattice vibration induces the conduction and in consequence the carrier mobility shows temperature dependence characterized by activation energy. For such a process of jumping of electrons and holes, the mobility are given by ( E1) K BT 1 el1f1e KT (1.7) ( E 2 ) K BT 2 el2f 2e KT (1.8) where the subscripts 1 and 2 represent the parameters for electrons and holes, l represents the jumping length, f 1 and f 2 represents lattice frequencies active in the jumping process, E 1 and E 2 are activation energies involved in the required lattice deformation.

17 17 The general expression for the total conductivities in this case where we have two types of charge carriers can be given as n (1.9) 1e 1 n 2e 2 The temperature dependence of conductivities arises only due to mobility and not due to the number of charge carriers in the sample Small Polaron Model Small polaron model was introduced by Haubenreisser (1961). A small polaran is a defect created when an electronic carrier becomes trapped at a given site as a consequence of the displacement of adjacent atoms or ions. The entire defect (carrier plus distortion) then migrates by an activated hopping mechanism. Small polaron formation can take place in materials whose conduction electrons belong to incomplete inner (d or f) shells which due to small electron overlap, tend to form extremely narrow bands. The migration of small polaron requires the hopping of both the electron and the polarized atomic configurations from one site to an adjacent site. Thus if the hopping electron becomes localized by virtue of its interaction with phonons, then a small polaron is formed and the electrical conduction is due to hopping motion of small polarons. 1.7 FERRITE NANOMATERIALS The unusual magnetic properties exhibited by ferrite nanoparticles and their promising technological applications have attracted much interest in recent years. Rapid advances in information, telecommunication and energy technology coupled with the need to reduce the size and cost of device drive this field of research. Ferrites nonoparticles are also regarded as important magnetic material because of their high electrical resistivity. The

18 18 nanostrcutured ferrites materials made of nanosized grains as building blocks, have a significant fraction of grain boundries with a high degree of disorder of atoms along the grain boundries. These act as scattering centers for the flow of electrons and therefore the resistivity increases. With improvement in synthesis and characterization techniques in nanometric range, there is a tremendous growth in the field of ferrites. Super paramagnetisim, spin canting, core/shell structure, metastable cation distribution etc. are some of the phenomena, which have been observed in nano particles of various ferrites. These phenomena depend on number of factors such as composition, grain size, surface morphology, anisotropy and interparticle interactions (Coey and Khalafella 1972; De Heer 2000; Nalwa 2002).The magnetic and the electrical properties of ferrites are reported to be highly sensitive to the cation distribution, which in turn depend on the material of synthesis and sintering conditions. Various preparation techniques have been used for synthesis of fine particles of ferrites, which exhibit novel properties when compared to their properties in bulk. Physical methods like mechanical milling present a high degree of crystalline defects. Goya and Rechenberg (1999) have reported that oxygen ions escape from the spinel structure, thereby creating anion vacancies during milling. Non-conventional methods such as co-precipitation, thermal decomposition, sol gel and hydrothermal methods have been widely used. Co-precipitation is an attractive method of producing ferrites because of increased homogeneity, purity and reactivity. They are relatively simple, low cost and particle size control can be easily achieved. Ferrite nanoparticles find application in the field of ferrofluids. Ferrofluids are used as liquid heat carriers in different heat exchange device (Auzans et al 1999). Ferro fluids retain the properties of liquid even in the presence of high magnetic fields, in which particles do not separate from the carrier liquid. These fluids are used in variety of applications such as targeted

19 19 drug delivery (Alexiou et al 2002; Voltairas et al 2002) and magnetocytolysis agent for treatment of localized cancerous cells. Hyperthermia is a therapeutic procedure, which is used to raise the temperature of region of the body affected by cancer 40 C to 46 C. Cancer cells are considered to be more sensitive to heat than normal cells. Higher temperature weakens cancer cells and enhances their sensitivity to chemotherapy and radiation therapy (Akin 2009). This method involves the introduction of ferromagnetic nanoparticles into tissues and their subsequent irradiation with an alternating electromagnetic field. Hyperthermia is an promising approach in cancer therapy. The challenge in this method is to restrict the local heating of the tumor surrounding. When exposed to alternating magnetic field, magnetic particles can generate heat via four different mechanism. They are a) by generation of eddy currents in magnetic particles, b) by the hysteresis losses in magnetic particles, c) by the relaxation losses in superparamagnetic singledomain magnetic particles and d) by the frictional losses in viscous suspensions. The main focus of research in the 21st century is towards the formation of smaller magnetic particles. So processing of ferrites has gained tremendous importance in recent times to meet the high performance demands of ferrites. The performance of ferrites is known to be sensitive to their processing technique (Parvatheeswara Rao et al 2006). Manganese Zinc ferrites and Nickel Zinc ferrites are still by far the most important ferrites for high permeability and low loss applications. Manganese Zinc ferrites have been widely used in electronic applications such as transformers, coils, recording heads etc. Nickel Zinc ferrites have been extensively used in large number of devices and component such as phase shifters, circulators, isolators, inductors and transformers. Verma et al (2006) have developed a new soft ferrite core for power applications using manganese substituted nickel zinc ferrite. Synthesis of nano sized Mn (1-x) Cd x Fe 2 O 4 at low temperature have been reported in the literature (Rajesh Iyer et al 2009).

20 20 Ferrofluids of Co 0.5 Zn 0.5 Fe 2 O 4 and Mn 0.5 Zn 0.5 Fe 2 O 4 nanoparticles have been prepared by co-precipitation method and characterized by X-ray diffraction, Vibrating sample magnetometer and Mossbauer studies (Arulmurugan et al 2006). 1.8 AIM OF THE PRESENT WORK With a view to understand the effects of nickel, cadmium and bismuth on the properties of nanosized manganese zinc ferrites, we have undertaken the preparation of Mn-Ni-Zn ferrite, Mn-Zn-Cd ferrite and bismuth substituted Mn ferrite by co-precipitation method. The main objective of the present work 1. To synthesis a single phase spinel ferrite nanoparticles. 2. To study the relationship between structural parameters and different concentration of the substituted magnetic and non magnetic ions like Ni and Cd in Mn-Zn ferrites. 3. To study the effect of cation distribution on the structural, magnetic and dielectric properties. 4. To study the variation of saturation magnetization, coercivity and curie temperature with different concentration. 5. To study the variation of dielectric constant, dielectric loss and dc resistivity with different concentration. 6. To study the substitution effect of bismuth on the properties of Mn ferrite.

21 21 The outcome of the research can be applied to fabricate quality microwave and magnetic storage devices leading to better life style. In addition to the above mentioned application, ferrites also have the following potential applications in the field of ferrofluids, drug delivery system, magnetic resonance imaging (MRI), hyperthermia and nano sensors.