Ilker Dincer

Gold-Coated Iron Composite Nanospheres Targeted the Detection of Escherichia coli

We report the preparation and characterization of spherical core-shell structured Fe3O4–Au magnetic nanoparticles, modified with two component self-assembled monolayers (SAMs) consisting of 3–mercaptophenylboronic acid (3–MBA) and 1–decanethiol (1–DT). The rapid and room temperature synthesis of magnetic nanoparticles was achieved using the hydroxylamine reduction of HAuCl4 on the surface of ethylenediaminetetraacetic acid (EDTA)-immobilized iron (magnetite Fe3O4) nanoparticles in the presence of an aqueous solution of hexadecyltrimetylammonium bromide (CTAB) as a dispersant. The reduction of gold on the surface of Fe3O4 nanoparticles exhibits a uniform, highly stable, and narrow particle size distribution of Fe3O4–Au nanoparticles with an average diameter of 9 ± 2 nm. The saturation magnetization value for the resulting nanoparticles was found to be 15 emu/g at 298 K. Subsequent surface modification with SAMs against glucoside moieties on the surface of bacteria provided effective magnetic separation. Comparison of the bacteria capturing efficiency, by means of different molecular recognition agents 3–MBA, 1–DT and the mixed monolayer of 3–MBA and 1–DT was presented. The best capturing efficiency of E. coli was achieved with the mixed monolayer of 3–MBA and 1–DT-modified nanoparticles. Molecular specificity and selectivity were also demonstrated by comparing the surface-enhanced Raman scattering (SERS) spectrum of E. coli-nanoparticle conjugates with bacterial growth media.

Inverse magnetocaloric effect of epitaxial Ni-Mn-Sn thin films

Epitaxial Ni-Mn-Sn thin films of 200 nm thickness were prepared by magnetron sputtering and deposited onto MgO(100) substrate. They reveal an inverse magnetocaloric effect with a martensitic phase transition around 260 K. The resulting magnetocaloric properties of these films have been determined performing magnetization measurements in the temperature range between 10 and 330 K applying different magnetic fields. The maximum values of entropy change and relative cooling power are 1.6 J kg−1 K−1 and 36.5 J kg−1 for cooling and 1.5 J kg−1 K−1 and 33.9 J kg−1 for heating in μ0ΔH=1 T, respectively. These data are comparable with bulk values of Ni-Mn-Sn Heusler alloys.

Magnetic properties of Pr1−xGdxMn2Ge2

The structural and magnetic properties of Pr1−xGdxMn2Ge2 were studied by x-ray diffraction and magnetization measurements. The substitution of Gd for Pr leads to a linear decrease in the lattice constants and the magnetic interactions in the Mn sublattice cross over from a ferromagnetic character to an antiferromagnetic one. At low temperatures, the rare-earth sublattice also orders and reconfigures the ordering in the Mn sublattice. The spins in the Mn sublattice are arranged parallel to the Pr sublattice and antiparallel to the Gd sublattice. The results are collected in a phase diagram.

Magnetic phase transitions in PrMn2-xCrxGe2

Abstract The structural and magnetic properties of PrMn 2− x Cr x Ge 2 (0⩽ x ⩽1.0) were studied by X-ray diffraction and magnetization measurements. The powder samples crystallize in the ThCr 2 Si 2 -type structure, and the lattice constants at room temperature show almost no variation as Cr substitutes Mn. The observed phase transitions are summarized in a proposed magnetic x − T phase diagram and compared with previous Moessbauer spectroscopy and neutron diffraction results for x =0.

Magnetic interactions in PrMn2−xCoxGe2

Abstract The structure and magnetic properties of PrMn 2− x Co x Ge 2 (0.0≤ x ≤1.0) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr 2 Si 2 -type structure with the space group I4/mmm . Substitution of Co for Mn led to a linear decrease in the lattice constants a and c and the unit cell volume. For samples with x ≤0.7, the ferromagnetic interlayer alignment of the Mn sublattice occurs below the Curie temperature. At low temperatures, the rare earth sublattice also orders and rearranges the ordering in the Mn sublattice. By comparing our results to earlier neutron diffraction and Mossbauer studies, it is concluded that the features observed in the temperature dependence of the magnetization above the Curie temperature is related to antiferromagnetic coupling within each Mn layer. For samples with x ≥0.8, the antiferromagnetic intralayer alignment of the Mn sublattice occurs below the Neel temperature. The results lead to the construction of the magnetic phase diagram.

Magnetic phase transitions in Pr1−xDyxMn2Ge2 and Ce1−xDyxMn2Ge2

The magnetic properties of the compounds Pr1−xDyxMn2Ge2 (0 ≤ x ≤ 1) and Ce1−xDyxMn2Ge2 (0 ≤ x ≤ 1) were investigated by means of temperature-dependent DC magnetization measurements in low external magnetic fields. The substitution of Dy for Pr or Ce leads to a linear decrease in the lattice parameters. Below about 330 K, the interlayer magnetic coupling in the Mn sublattice is ferromagnetic for Pr-rich and Ce-rich compounds and antiferromagnetic for Dy-rich compounds. At low temperatures, the Dy sublattice also orders and reconfigures the ordering in the Mn sublattice. This leads to ferrimagnetic ordering for Dy-rich compounds.

Magnetocaloric properties of the Gd5Si2.05–xGe1.95–xMn2x compounds

Abstract The influence of the manganese-alloying on the structure and magnetocaloric properties of the Gd5Si2.05Ge1.95 compound was studied by X-ray powder diffraction and magnetization measurements. The Gd5Si2.05–xGe1.95–xMn2x (2x=0, 0.03 and 0.08) compounds crystallized in the Gd5Si2Ge2-type monoclinic structure. In all X-ray powder diffraction patterns, a minor hexagonal Gd5Si3 phase was observed as a second phase. With increasing Mn content, the unit cell volume increased. For the compounds with x=0, 0.03 and 0.08, the first order phase transition was observed. The maximum isothermal magnetic entropy change of the Gd5Si2.05–xGe1.95–xMn2x compound with 2x=0.03 at 275 K was found to be −11.6 J/(kg·K) in an applied field of 5 T.

Structure and giant inverse magnetocaloric effect of epitaxial Ni-Co-Mn-Al films

In the ongoing search for magnetocaloric materials, Heusler compound based ferromagnetic shape memory alloys (FSMA) of the system Ni-Mn-Z (Z=Sb, Ga, In, Sn) turned out to be very promising due to low cost of the containing elements and sizable magnetocaloric effects (MCE).[1] Substitution of Ni against Co in Ni-Mn-Z is known to improve the metamagnetic behavior of the martensitic transition, and thus the magnetocaloric properties as it increases the austenite Curie temperature T C A and leads to a transition from weak magnetic martensite to ferromagnetic austenite. Off-stoi-chiometric Ni-Mn-Al also shows a martensitic transition but accompanied by only small changes in the magnetization and hence neglectable MCE.[2] Substitution of up to 10at.% Co for Ni strongly promotes the ferromagnetism in the austenite phase and leads to a metamagnetic martensitic transition.[3] The magnetization difference between austenite and martensite enables magnetic field induced reverse transition together with an inverse magnetocaloric effect.[4,5]

Magnetoresistance and magnetocaloric properties of the Pr0.1Gd0.9Mn2Ge2 compound

The magnetoresistance and magnetocaloric properties of the Pr0.1Gd0.9Mn2Ge2 compound have been investigated by resistance and magnetization measurements. This compound shows ferrimagnetism, antiferromagnetism, ferromagnetism, antiferromagnetism and paramagnetism with increasing temperature. The metamagnetic transition occurs from antiferromagnetism to ferrimagnetism and ferromagnetism at around TCR and TNinter, respectively. Magnetoresistance is observed at magnetic transition temperature, as expected. Normal and inverse magnetocaloric effects are observed at magnetic transition temperatures. Magnetic entropy changes are calculated from isothermal magnetization curves using Maxwells relation and Landau theory. Both the calculated magnetic entropy changes are in good agreement.

Inverse and conventional magnetic entropy change in La0.8Sm0.2Mn2Si2 and La0.775Gd0.225Mn2Si2 compounds

The magnetic and magnetocaloric properties of La0.8Sm0.2Mn2Si2 and La0.775Gd0.225Mn2Si2 compounds have been studied by temperature- and magnetic field-dependent magnetic measurements. Both compounds crystallize in the ThCr2Si2-type structure with the space group I4/mmm. Both compounds exhibit reentrant magnetic phase transitions and field-induced transitions from antiferromagnetic to ferromagnetic or ferrimagnetic state. The isothermal magnetic entropy change is estimated by using the Maxwell relation and Landau theory. Both compounds show inverse and conventional magnetocaloric effects around transition temperatures. Application of Landau theory on magnetic transitions shows good agreement with the result obtained by Maxwell theory.