Synthesis & Characterization Of Magnesium Ferrite and Exploring its Microwave Application

An Overview Of Ferrites In 1950’s Magnetite (Fe3 O4 ), - lodestone, the first

magnetic material was known . Ferrites are iron containing complex oxides that

crystallize in the form of a cubic structure composed of different transition metals ( d-block elements ; group 3 to 12).

Each corner of a ferrite unit cell consists of a ferrite molecule .

Normally there are two types of structures in ferrites.Regular spinel Inverse spinel

Crystal Structure Of Ferrites

A Sublattice = Tetrahedral Site & B Sublattice = Octahedral Site .

8 divalent metal ions, 16 ferric ions and 32 Oxygen ions.Every 4 O2 ions = 2 octahedral sites + 1 tetrahedral site

(Types Of Ferrites)There are two types of ferrites :

Soft ferrites Low Coercivity means the material's magnetization can easily reverse direction without dissipating much energy (hysteresis losses), while high resistivity prevents eddy currents in the core. Hard ferrites High Coercivity means the materials are very resistant to becoming demagnetized, as in Permanent Magnet. Due to high magnetic permeability , these are called Ceramic magnets .

Alignment Of Domains In M-H Loop

Magnesium Ferrite

Crystalline magnesium ferrite is an n-type semiconducting material.

A soft magnetic material ( easy to magnetize & demagnetize). Low magnetic and dielectric losses. High resistivity, magnesium ferrite is used in microwave devices such as phase shifters,

circulators etc.

Stability over wide range of temperature.

Excellent magnetic behavior due to strong exchange interactions & ordering of magnetic moments of ferric ions.

High permeability and time/temperature stability have expanded the usage of soft ferrites in high frequency and delay lines, broadband transformers, adjustable inductors.

Synthesis Of MgF using Co-Precipitation

Formation Of Nanosized FerritesFormation of Nanosized ferritesM2+ + 2Fe3+ + 8OH¯ → MFe2O4 + 4H2Oprecipitation in the form of metal hydroxides at a pH between 8 and 14 by adding a precipitating agent such as NaOH, NH4OH , with a stoichiometric ratio of 2:1 (Fe3+/M2+) in a non-oxidizing oxygen environment .

Hydroxides are annealed after filtration and washing to get the final oxide powder. Due to ferrimagnetic nature, the magnetic properties of spinel ferrites depend strongly on the distribution of cations between the A-and B-sites.

Size ,Shape & Composition Of magnetic nanoparticles depend on the type of salts used (e.g. Chlorides, sulfates, nitrates), the Fe2+/Fe3+ ratio, the reaction temperature, the pH value and Ionic strength of the media.

Sample Preparationa) The desired metallic salts (Precursors) i.e. 1M of Mg(NO3)2.6H2O (i.e. 4.04gm in 10ml

water) and 1M of Fe(NO3)3.9H2O (i.e. 2.56gm in 10ml water), are dissolved in de-ionized water and mix together in an appropriate stoichiometric ratio in a beaker.

b) 0.2M Ammonium hydroxide solution is added for the precipitation at pH 9-10. The mixture is stirred for 3 hrs with a slight warming followed by an overnight aging.

c) The collected precipitates comprising of hydroxides of metal ions, ammonium nitrates and some water contents , have been repeatedly washed with de-ionized water and ethanol in order to remove the excess ammonia, any un-reacted species.

d) After that dried at 403 K in an oven to remove the water contents, followed by grinding the dry precipitate to powder form , in order to break coarse particles uniformly.

e) The dried product obtained is sintered at 300 degrees for 2 hrs, followed by sintering at 850 degrees for 4 hours.

f) The grinding is done using an Agate mortar-pestle

g) After this the powdered ferrite is made in to pellets of size 22.8mm X 10.13mm for X-Band Microwave Frequency .

h) The powdered samples are also pressed at 10Kn to form pellets of 13 mm in diameter and ~2 mm thickness and have been used in microwave measurements .

i) Then pellets are annealed at 850 degrees where it achieved the maximum magnetization of 20.18Amu/gm in a set temperature tube furnace at a heating rate of 5 Kmin-1. The following reaction may occur: Mg(NO3)2 (aq) + 2Fe(NO3)3 (aq) + yNH4OH------ 6NH4NO3 [Mg2+Fe3+.OH-]m + yNH4NO3 [Mg2+Fe3+.OH-]m͢͢MgFe2O4

j) Structural characterization of samples was carried out by X-ray diffraction (XRD Rigaku MinifleXII , Step size=0.02). k) The Ferrite sample was inserted in to a standard coaxial sample holder and the Reflection Coefficient (S11 parameter) and Transmission Coefficient (S21 parameter) were measured by an Agilent E836B Vector Network Analyzer(VNA) in frequency range of 8-12Ghz.. l) Magnetic measurements were performed at room temperature by plotting M-H curves for the samples using VSM(Lakeshore 7304).

Characterization TechniquesThe following characterizations have been potentially performed for the analysis of the synthesized samples. Powder X-ray diffraction technique (XRD)

o Phase identification

o Lattice parameters determination Field Emission Scanning electron microscopy (SEM)

o Surface morphological and microstructural analysis

Vibrating sample magnetometer (VSM)

Results For XRD• The XRD pattern of the Magnesium Ferrite sample after being annealed at 850 degrees

represents the typical Hexagonal Structure. The increasing curve base of the MgF sample exhibits Nanocrystalline behavior of pure phase MgF.

• According to Scherrer Formula, crystallite size of MgF is_________

Field Emission Scanning electron microscopy (FESEM)

FESEM AnalysisSAMPLE NUMBER MAGNIFICATION PARTICLE SIZE SE2 41.70KX 80-300nm grain

size

SE2 50.63KX Micropores & Nanopores of 100-50nm. Porous Structure with particle size 70-100nm.

SE2 500X Porous sample surface

SE2 100KX Uniformly distributed grains of MgF in the range of 100-300nm with less porosity.

•

As Prepared Sample Sintered At 750

degrees

RESULTS OF VIBRATING SAMPLE MAGNETOMETER

Pellet

SAMPLE

ANNEALING TEMPERATURE

MAGNETIZATION

COERCIVITY

MAGNETIC NATURE OF SAMPLE

SE1 As Prepared 0.696emu/g

- No Loop

SE1 750 Degrees 7.9062emu/g

117.10G Ferromagnetic

SE1 950 Degrees(Pellet)

20.805emu/g

63.567G Ferromagnetic with very small particle size & Low Coercivity.

Microwave Absorption When an electromagnetic wave propagates in free space in to the materials, some of the

energy in the wave is reflected and the rest is transmitted in to the material. If the internal impedance is closer and equal to the external impedance , the transmission coefficient increases and the reflection coefficient decreases.

The EMI shielding effectiveness(SE) of a material is defined as the ratio of transmitted power to incident power and is given by

SE(dB) = -10log(Pt/Po) Where Pt and Po are transmitted and incident electromagnetic powers respectively. For a

shielding material , total SE=Sum of SE of reflection, absorption and multiple reflections.

If the effect of multiple reflections between both interfaces of the material is negligible, the relative intensity of the effectively incident EM wave inside the material after reflection is treated equal to 1-R .

Hence, the effective absorbance (Aeff) can be described as Aeff=(1-R-T)/(1-R) with respect to the power of the effectively incident EM wave inside the shielding material.

The real part E is mainly associated with the amount of polarization occurring in the material and the imaginary partE” is related with the dissipation of energy in the form of dielectric losses.

MICROWAVE ABSORPTION MEASUREMENT USING VNA(VECTOR NETWORK ANALYZER)

FREQUENCY(Ghz) RETURN LOSS(db) PHASE MAGNITUDE(Degrees)

9 0.275 126.5

10 0.227 107.84

11 0.094 81.40

12 0.874 103.93

S11-(With Sample) Transmittance

S11-(without Sample) Transmittance

FREQUENCY(Ghz) RETURN LOSS(db) PHASE MAGNITUDE(Degrees)

9 0.336 129.08

10 0.248 111.10

11 0.171 89.70

12 0.815 111.95

S21-Reflectance(With MismatcH)

FREQUENCY(Ghz) RETURN LOSS(db) PHASE MAGNITUDE(Degrees)

9 -0.089 -76.08

10 -0.219 -94.35

11 -0.0143 -108.43

12 -0.108 -124.07

S21-Reflectance(With Sample)

FREQUENCY(Ghz) RETURN LOSS(db) PHASE MAGNITUDE(degrees)

9 -0.679 68.05

10 -0.675 44.94

11 -0.703 11.36

12 -1.668 17.88

Text & References• Safarik, I.; Safarikova, M. Magnetic Nanoparticles and Biosciences, Monotshefte fur Chemie, Frankfurt, 2002, 133,

737-759. • • Buzea, C.; Pacheco, I.; Robbie, K. Biointerphases, 2007, 2, MR17- MR71. • • Allhoff, F.; Lin, p.; Moore, D. What is Nanotechnology and why does it Matter? • • John Wiley and Sons, New York, 2010, pp. 3. • • Sohn, B.H.; Cohen, R.E. Chem. Mater. 1997, 9, 264-269. • • Klabunde, K.J. Nanoscale Materials in Chemistry, Wiley, New York, 2001, pp.1. • • Adams, D.M. Inorganic Solids, John Willey, London, 1974, pp. 68. • • Smyth, D.M. The Defect Chemistry of Metal Oxides, Oxford University Press, New York, 2000, Chap. 2, pp. 35. • • West, A.R. Solid State Chemistry and its Applications, John Wiley & Sons, Singapore, 1989, Chap.16, pp. 571. •