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Arshi, Nishat,Ahmed, Faheem,Kumar, Shalendra,Anwar, M.S.,Lu, Junqing,Koo, Bon Heun,Lee, Chan Gyu Elsevier 2011 Current Applied Physics Vol.11 No.1
<P><B>Abstract</B></P><P>We report a simple one step microwave irradiation method for the synthesis of gold nanoparticles using citric acid as reducing agent and cetyl trimethyl ammonium bromide (CTAB) as binding agent. The reaction was completed under two different microwave irradiation times (40 s and 70 s) for the production of two types of gold nanoparticles. The synthesized nanoparticles were characterized using UV–Vis absorption spectroscopy and transmission electron microscopy (TEM) measurements. UV–Vis study revealed the formation of gold nanoparticles with surface plasmon absorption maxima at 590 and 560 nm for 40 and 70 s irradiation time respectively. From TEM analysis, it is observed that the gold nanoparticles have spherical shape with particle size distribution in the range 1–10 nm and 1–2 nm for 40 s and 70 s irradiation time respectively. Antibacterial activity of gold nanoparticles as a function of particle concentration against gram-negative bacterium <I>Escherichia coli</I> (<I>E. coli</I>) was carried out in solid growth media. The two types of gold nanoparticles show high antibacterial activity with zone of inhibition of about 22 mm against <I>E. coli</I> (ATCC 25922 strain). Very small difference in the antibacterial activity for the two types of gold nanoparticles were observed. Though nanoparticles synthesized for 70 s irradiation time show slightly better antibacterial activity.</P> <P><B>Highlights</B></P><P>► Gold nanoparticles have been successfully synthesized using microwave irradiation technique. ► The mean diameter was ∼ 4.05 nm for 40 s and ∼1.05 nm for 70 s. ► Characteristic absorption peak was found to be 590 nm for 40 s and 560 nm for 70 s. ► The zone of inhibition for the two types of nanoparticles was almost similar (22 mm). ► Smaller size nanoparticles synthesized for 70s showed a slightly better antibacterial action.</P>
Anwar, M.S.,Ahmed, F.,Koo, B.H. Elsevier Science 2014 Acta materialia Vol.71 No.-
We report on a detail study of the structural, magnetic and magnetocaloric properties of Zn-doped nickel-zinc ferrites with different Zn concentrations. Polycrystalline Ni<SUB>1-x</SUB>Zn<SUB>x</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> (0.0≤x≤0.7) ferrite samples were prepared using the conventional solid-state reaction method. The X-ray diffraction results indicate that the ferrite samples have a cubic spinel type structure without any impurity phase. Temperature-dependent magnetization measurements and Arrott analysis reveal second-order ferromagnetic transition in all samples, with the Curie temperature decreasing progressively with increasing Zn concentration, from ~845K for x=0.0 to 302K for x=0.7. An increase in magnetization at low temperature was observed for Zn doping up to x=0.5. A maximum in magnetic entropy change, |ΔS<SUB>M</SUB><SUP>max</SUP>| (~1.39Jkg<SUP>-1</SUP>K<SUP>-1</SUP> at 2.5T), was observed in the Ni<SUB>0.7</SUB>Zn<SUB>0.3</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> sample. The width of magnetic entropy curve was found to increase with the Zn concentration. Also, the |ΔS<SUB>M</SUB><SUP>max</SUP>| and relative cooling power were found to increase with increasing applied magnetic field, which indicates much greater cooling power is expected with a larger magnetic field. This investigation suggests that Ni<SUB>1-x</SUB>Zn<SUB>x</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> (0.0≤x≤0.7) ferrite samples are possible candidates for magnetic refrigeration across a wide range of working temperatures.
Anwar, M. S.,Cho, Hyeon Ji,Hussain, Imad,Koo, Bon Heun American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.11
<P>The structural, magnetic and magnetocaloric properties of (1-y)LSMO/(y)Mn0.5Zn0.5Fe2O4 (y = 0.00, 0.03, 0.05, 0.10) composite samples have been studied. All samples show mainly pervoskite phase with rhombohedral crystal lattice. The XRD peaks of Mn0.5Zn0.5Fe2O4 phase were not observed because of its very low concentration in the composite sample. The magnetization measurement reveals that the Curie temperature, T-C decreases significantly with increasing the Mn0.5Zn0.5Fe2O4 concentration in the composite samples. On the other hand, the temperature range of paramagnetic-ferromagnetic transition becomes broader in case of composite samples. The magnetic entropy evaluation shows that the Delta S-M(max) decreased in case of composite samples as compared to that of pure LSMO sample. In addition, an enhanced relative cooling power of 57 J/kg (at 1 T) was observed for the (0.97) LSMO/(0.03)Mn0.5Zn0.5Fe2O4 composite sample, which is due to the increased partial derivative T-FWHM over 62 K around room temperature.</P>
Magnetization and Magnetocaloric Effect in Sol-Gel Derived Nanocrystalline Copper-Zinc Ferrite.
Anwar, M S,Ahmed, Faheem,Koo, Bon Heun American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.2
<P>We report the sol-gel synthesis and magnetocaloric effect in nanocrystalline copper-zinc ferrite (Cu0.5Zn0.5Fe2O4). The synthesized powder was characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and magnetization measurements. The XRD results confirm the formation of single phase spinel structure. The average particle size was found to be ~58 nm. FE-SEM results suggested that the nanoparticles are agglomerated and spherical in shape. Magnetization measurement reveals that Cu0.5Zn0.5Fe2O4 nanoparticles exhibit transition temperature (Tc) above room temperature. The maximum magnetic entropy change (??SM)max shows interesting behaviour and was found to vary with the applied magnetic field. This nanopowder can be considered as potential material for magnetic refrigeration above room temperature.</P>
Anwar, M.S.,Ahmed, F.,Koo, B.H. Elsevier Sequoia 2014 JOURNAL OF ALLOYS AND COMPOUNDS Vol.617 No.-
Polycrystalline La<SUB>0.65-x</SUB>Pr<SUB>x</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> (0.0≤x≤0.3) manganite samples were prepared using the conventional solid-state reaction method. The X-ray diffraction result indicates that the all samples have rhombohedral (R-3c) structure without any impurity phase. The field-cooled magnetization M(T) of all samples show the ferromagnetic behavior below Curie temperature (T<SUB>C</SUB>). Also, the saturation magnetization and T<SUB>C</SUB> of the samples decreases and the transition become broader with increasing the Pr concentration. The Arrott plot analysis reveals the second order of ferromagnetic transition at T=T<SUB>C</SUB> for all samples. Magnetic entropy change was evaluated from magnetization isotherms. The magnitude of the isothermal magnetic entropy change is nearly composition independent (1.1+/-0.15Jkg<SUP>-1</SUP>K<SUP>-1</SUP> for ΔH=1T) and relative cooling power lies between 48.85 and 33.10J/kg for 0.0≤x≤0.3. The phenomenon of reversible entropy change and the convenient adjustment of the Curie temperature by Pr doping, make these samples as a possible candidate for magnetic refrigeration at room temperature.