MnxCo1-xFe2O4 nanoparticles were successfully synthesized by polyethylene glycol (PEG)-assisted hydrothermal route. XRD, FT-IR, SEM and VSM were used for the structural, morphological, and magnetic investigation of the products, respectively. Average particle sizes of the nanoparticles were estimated using the line profile fitting and found between 43-55 nm. Magnetization measurements have shown that the particles have varying blocking temperatures depending on Mn concentration. While the nanoparticles indicate a superparamagnetic behavior above the blocking temperature they show ferromagnetic behaviors at temperatures lower than the blocking temperature. Magnetization and the coercive field of the samples increase by decreasing the temperature. It is observed that the dc conductivity increases with increasing temperature indicating the semiconducting nature of the samples. Dielectric properties of the samples show the frequency-dependent phenomena i.e. the dielectric constant decreases with increasing frequency which is a normal behavior observed in most of the ferrimagnetic materials, which is attributed to the interfacial polarization as predicted by Maxwell–Wagner.
Nanosized spinel ferrites are interesting materials and have attracted considerable interest, and efforts in the last decades because of the large number of applications where they can be used: ferrofluids, magnetoptics, spintronics, microwave industries, disk recording, refrigeration systems, electrical devices, anodes for batteries, etc. [1-5]. The magnetic and dielectric properties of spinel ferrites can be varied systematically by changing the identity of the divalent Me2+ cations (Me=Co, Mn, Ni, Zn, etc.) without changing the spinel crystal structure [6-8]. The magnetic and dielectric properties of nanosized particles show large differences when compared to bulk materials and they are widely studied because of the demanding increase in miniaturization and data storage densities. When the particle size is reduced, the surface-to-volume ratio becomes larger and the magnetic characteristics are strongly affected due to the inﬂuence of thermal energy over the magnetic moment ordering, originating the superparamagnetic phenomenon [5, 7-9].
Cobalt ferrite, CoFe2O4, is a well-known hard magnetic material, which has been studied in detail due to its high coercivity (5400 Oe) and moderate saturation magnetization (*80 emu/g) at room temperature. However, in the case of nanosized CoFe2O4 particles, different values of coercivity and saturation magnetization have been reported [9-12]. The reason is that the magnetic properties of nanosized particles depend on the particle size and the preparation method. Coey (1971) explained the reduction of saturation magnetization of nanosized ferrites by considering a spin conﬁguration that differs from the Neel type found in large particles. He proposed that the spins are canted at the surface of the nanoparticles; i.e., the ions in the surface layer are inclined at various angles respect to the direction of the net moment. In this way, the particle magnetization cannot be seen as uniform through the nanoparticle and it is the result of a magnetic ordered core and a surrounding surface shell of disordered spins [5, 8, 13].
In the present study, we have successfully synthesized Mn doped CoFe2O4 (MnxCo1-xFe2O4 x= 0-1) nanoparticles by using polyethylene glycol (PEG)-assisted hydrothermal route in order to investigate effect of Mn doping on magnetic and dielectric properties of CoFe2O4 nanoparticles. Then we used XRD, FT-IR and SEM for structural characterization. From magnetization measurements it is observed that the particles exhibit superparamagnetic and ferromagnetic behaviors depending on the Mn concentrations and the blocking temperatures decrease by Mn concentration. While the coercive field of the samples decrease by the Mn concentration the magnetization increase. They also increase by decreasing the temperature. DC conductivity increases with increasing temperature which indicates the semiconducting nature of the samples. Dielectric properties of the samples also show the frequency-dependent phenomena i.e. the dielectric constant decreases with increasing frequency which is a normal behavior observed in most of the ferrimagnetic materials, which is attributed to the interfacial polarization as predicted by Maxwell–Wagner.
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1992, B.Sc. Physics Education, Middle East Technical University
1997, M.Sc. Physics, Fatih University
2003, Ph.D. Physics, Gebze Institute of Technology
* Sokrates/Erasmus Faculty Coordinator Fatih Üniversitesi, Nov. 2007-now
* Deputy Dean. Fatih Üniversitesi, Sep. 2007-now
* Assoc. Prof. Dr. Interuniversity Council, Jan. 2007
* Coordinator of General Physics Courses, Fatih University, Oct. 2006- Sep. 2009
* Asst. Prof. Dr. Fatih Üniversitesi, Apr. 2004- Jan. 2007
* Lecturer, Fatih University, Oct. 1999- Nov. 2003
* Research assistant, Fatih University, Oct. 1997- Oct. 1999
Electron Paramagnetic Resonance(EPR), Ferromagnetic Resonance(FMR), Dielectric Spectroscopy, Synthesis and characterizations of Magnetic nanopowders nanoparticles, and quantum dots (Me doped ZnO), Coated magnetic nanoparticles of spinel ferrites, Dielectric properties of spinel ferrites, Magnetic gas sensors,