Hakan Kockar

A Simple Way to Synthesize Superparamagnetic Iron Oxide Nanoparticles in Air Atmosphere: Iron Ion Concentration Effect

We have synthesized iron oxide nanoparticles in air atmosphere by coprecipitation. The ratio of was fixed at 2/3. The total amount of iron ions in the solution was varied from 250 mmol to 12.5 mmol. X-ray diffraction (XRD) patterns showed the characteristic peaks of iron oxide phases. We observed that the crystallinity reduced and particle sizes calculated from XRD patterns decreased as the iron ion concentration in the solution decreased. Fourier transform infrared spectroscopy analysis exhibited the Fe-O vibration band at 560-580 confirming the iron oxide formation. The mean physical sizes obtained from a transmission electron microscope are around 8 nm. According to the magnetic measurements, all samples are superparamagnetic at room temperature showing an increase in saturation magnetization up to 63.71 emu/g. Magnetic sizes of the particles vary from 7.45 nm to 4.88 nm with the change of iron ion concentration.

Iron Oxide Nanoparticles Co-Precipitated in Air Environment: Effect of [Fe

Iron oxide nanoparticles (IONs) were synthesized from ferrous aqueous solutions in air atmosphere by co-precipitation. The effect of [Fe+2]/[Fe+3] ratio on the properties of the nanoparticles were investigated. X-ray diffraction (XRD) patterns showed the charac- teristic peaks of iron oxide for all samples. Fourier transform infrared spectroscopy analysis also confirmed the iron oxide formation. According to magnetic measurements, saturation magnetization, Ms of the nanoparticles increased from 37.6 emu/g to 59.4 emu/g with the increase of [Fe+2]/[Fe+3] ratio from 1/2 to 6/6 and the samples are superparamagnetic with zero coercivities. However, with the increase of the ratio above 6/6 the samples start to show coercivities (8 Oe, 22 Oe and 33 Oe) and Ms increases up to 74.3 emu/g. Particle sizes calculated from the XRD patterns, the images of the transmission electron microscope and magnetic data are consistent with each other and increased with the increase of [Fe+2]/[Fe+3] ratio. It is revealed that the particle size, Ms and magnetic character of IONs were significantly influenced by [Fe+2]/[Fe+3] ratio. Below the critical size of ~11 nm it is seen that IONs showed superparamagnetic character with zero coercivity.

^{+2}

A series of CoNiCu/Cu multilayers was potentiostatically electrodeposited on strong 100 textured Cu substrates from electrolytes with different Ni concentrations. X-ray diffraction patterns showed that all studied samples exhibited a face-centered cubic structure. From scanning electron microscopy images, it was observed that the surface morphology of the films is affected by their Ni content. The compositional analysis by energy-dispersive X-ray spectroscopy demonstrated that as the Ni ion concentration in the electrolyte is increased, the Ni content of the film increases. Magnetoresistance MR measurements were carried out at room temperature in the magnetic fields of 12 kOe. The samples grown from the electrolytes with the Ni concentration of up to 0.3 M exhibited giant magnetoresistance GMR. For the samples grown from 0.3 M Ni, anisotropic magnetoresistance AMR begins to appear as well as GMR. As the Ni concentration in the electrolytes is increased, the AMR effect enhances, whereas the GMR effect weakens. For the 2.0 M Ni concentration, the MR behavior of multilayers converts from GMR to AMR. Furthermore, the magnetization measurements made by a vibrating sample magnetometer showed that the antiferromagnetic coupling between ferromagnetic layers weakens with increasing the Ni concentrations.

]/[Fe

Co-Fe films were electrodeposited on Titanium substrates at the cathode potentials changing from - 1.8 to - 2.7 V with respect to saturated calomel electrode (SCE). The structural analysis by X-ray diffraction revealed that all films have a mixed phase of face centered cubic and body centered cubic structure, but the phase ratios change depending on the cathode potentials. The compositional analysis, which was made using an energy dispersive X-ray spectrometry, demonstrated that the Co content of the films slightly increases as the deposition potential increases. The morphological analysis of the films grown at high deposition potential (-2.7 V versus SCE), studied by scanning electron microscopy, indicate that they have larger grains. All Co-Fe films showed anisotropic magnetic resistance up to 4% and its magnitude was affected by the cathode potentials. Magnetic measurements carried out by the vibrating sample magnetometer indicated that the saturation magnetization varied and the coercivity decreased from 46.98 to 31.74 Oe as the cathode potential increased. The easy axis of magnetization was found to be in the film plane for all films. The variation in magnetoresistance and magnetic properties may be related to the structural changes in the films.

^{+3}

We have investigated the effect of fabrication conditions on the magnetic anisotropy of iron films produced by a novel rotating cryostat (RC) system. Clamped films exhibited uniaxial in-plane anisotropy with the easy axis in the film plane and perpendicular to the rotation direction of the RC system. An unclamped one showed no uniaxial magnetic anisotropy.

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Abstract A novel rotating cryostat vacuum system originally designed to fabricate organic layers has been used for the first time to evaporate 3% silicon–iron magnetic materials. Results of all films deposited on glass and silicon exhibit isotropic magnetic behaviour but the films produced on kapton generally show an in-plane magnetic anisotropy within the film plane. Results were also confirmed with the laser-ablated films.

Magnetoresistance of CoNiCu/Cu Multilayers Electrodeposited from Electrolytes with Different Ni Ion Concentrations

The structural and magnetic properties of Co-Cu films were studied in terms of Co content in the films. The surface morphology of the films showed that the film with the lowest Co content (3 wt. %) had dendritic structures, whereas the surface of the film containing the highest amount of Co (61 wt. %) was more uniform with acicular shapes in some parts. X-ray diffraction patterns of the films showed that their crystal structure is a mixture of dominantly face-centered cubic (fcc) and hexagonal close-packed phases. At the lowest Co content, separate fcc (111) peaks appear, whereas the increase of Co content converts the peaks to be a single broad Co-Cu peak. The vibrating sample magnetometer measurements revealed that the saturation magnetization increases and coercivity decreases due to the decrease of the grain size caused by the increase of the Co content in the film. The structural and magnetic properties of Co-Cu films can be tailored, since these properties are directly related to the ratio of Co to Cu in the film.

Properties of Co–Fe Films: Dependence of Cathode Potentials

Abstract The factors determining the magnetic properties of iron films evaporated from an evaporation source positioned around a novel rotating cryostat (RC) system have been discussed. Results show all films exhibit isotropic behaviour when the RC system is stationary irrespective of the types of substrates used. However, when the RC is rotated, the films produced on kapton™ generally show a slight in-plane anisotropy.

The rotation and clamping effect on the magnetic properties of iron films deposited onto a rotating substrate

A rotating cryostat vacuum system has been used to deposit Si3Fe97 magnetic films. Observations indicate that inplane magnetic anisotropyand coercivityis dependent on the ty pe of substrate and the deposition method used. The findings are discussed with concern to scaling up the technique for the production of strip shaped components. r 2002 Elsevier Science B.V. All rights reserved.

Characterisation of evaporated and laser-ablated 3% silicon–iron

Ternary NiCoFe films were potentiostatically electrodeposited from the electrolytes with low (3.0) and high (3.6) pH levels, and differences in their compositional, structural, magnetic and magnetoresistance properties were studied. The compositional analysis demonstrated that the Ni content in the films decreased, and Co and Fe content increased while electrolyte pH was changed from low to high level. The structural analysis of the films was carried out using the X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The XRD data revealed that the films have a strong (111) texture of the face-centred cubic (fcc) structure at low pH, while for the films at high pH a mixture of dominantly fcc and hexagonal closed packed structure was observed. The SEM studies showed that films grown at low pH level had comparatively larger grains than those at high pH. The magnetic characteristics studied by a vibrating sample magnetometer and magnetotransport properties were seen to be changed by the electrolyte pH. However, all films have in-plane magnetic anisotropy. The differences observed in the magnetic and magnetotransport properties were attributed to the microstructural changes caused by the electrolyte pH.