Magnetic Properties Of CoFe Research Articles

Characterization and magnetic properties of CoFe2O4 nanoparticles synthesized by the co‐precipitation method

AbstractIn this study, the characterization and magnetic properties of CoFe2O4 nanoparticles synthesized by co‐precipitation method were investigated. The calcined products obtained were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X‐ray (EDAX), Fourier transformed infrared (FTIR) spectroscopy, and vibrating sample magnetometer. Crystallite size and phase composition were analyzed by X‐ray diffraction. Crystallite size and phase composition were analyzed by X‐ray diffraction. The average crystallite size of CoFe2O4 nanoparticles increased in the range of 15.85–32.14 nm with an increase in temperature from 500 to 700°C. It was observed that spherical CoFe2O4 nanoparticles were produced. Synthesis of CoFe2O4 nanoparticles was confirmed using XRD, SEM‐EDAX, and FTIR analyses. The effect of crystallite size, calcination temperature, and lattice parameter on saturation magnetization, remanent magnetization, coercivity, and magnetocrystalline anisotropy were investigated by vibrating sample magnetometer. As the crystallite size value increased, magnetocrystalline anisotropy also increased.

Tuning the microstructural and magnetic properties of CoFe2O4/SiO2 nanocomposites by Cu2+ doping.

Co–Cu ferrite is a promising functional material in many practical applications, and its physical properties can be tailored by changing its composition. In this work, Co1−xCuxFe2O4 (0 ≤ x ≤ 0.3) nanoparticles (NPs) embedded in a SiO2 matrix were prepared by a sol–gel method. The effect of a small Cu2+ doping content on their microstructure and magnetic properties was studied using XRD, TEM, Mössbauer spectroscopy, and VSM. It was found that single cubic Co1−xCuxFe2O4 ferrite was formed in amorphous SiO2 matrix. The average crystallite size of Co1−xCuxFe2O4 increased from 18 to 36 nm as Cu2+ doping content x increased from 0 to 0.3. Mössbauer spectroscopy indicated that the occupancy of Cu2+ ions at the octahedral B sites led to a slight deformation of octahedral symmetry, and Cu2+doping resulted in cation migration between octahedral A and tetrahedral B sites. With Cu2+ content increasing, the saturation magnetization (Ms) first increased, then tended to decrease, while the coercivity (Hc) decreased continuously, which was associated with the cation migration. The results suggest that the Cu2+ doping content in Co1−xCuxFe2O4 NPs plays an important role in its magnetic properties.

Structure, microstructure and magnetic properties of pulse electrodeposited CoFe–Cu granular thin films

In this paper, we have investigated structural and magnetic properties of CoFe–Cu granular thin films as a function of ferromagnetic layer pulse time (tCoFe). These films were electrodeposited on Au-coated Si substrate from an aqueous solution containing boric acid and ascorbic acid as additives. Deposition potential for Cu layer was − 0.5 V and − 0.9 V for CoFe layer with respect to (AgCl/Ag) electrode. EDX analysis has shown that ferromagnetic material concentration increases with increase in ferromagnetic layer pulse time (tCoFe). The presence of (110) (200) (211) (311) and (220) XRD reflections observed at 2θ ~ 45°, 52°, 83°, 93°, and 99° indicate that these films have mixture of body-centered cubic and face-centered cubic structure. Magnetic measurements revealed that the easy axis of magnetization lies along the in-plane direction. Magnetic properties of granular films are explained by considering the changes in the elemental composition, deposition time, dynamics of the surface roughness, and anisotropy.

Magnetic Properties of CoFe2O4 Thin Films Synthesized by Radical-Enhanced Atomic Layer Deposition

A radical-enhanced atomic layer deposition (RE-ALD) process was developed for growing ferrimagnetic CoFe2O4 thin films. By utilizing bis(2,2,6,6-tetramethyl-3,5-heptanedionato) cobalt(II), tris(2,2,6,6-tetramethyl-3,5-heptanedionato) iron(III), and atomic oxygen as the metal and oxidation sources, respectively, amorphous and stoichiometric CoFe2O4 films were deposited onto SrTiO3 (001) substrates at 200 °C. The RE-ALD growth rate obtained for CoFe2O4 is ∼2.4 Å/supercycle, significantly higher than the values reported for thermally activated ALD processes. Microstructural characterization by X-ray diffraction and transmission electron microscopy indicate that the CoFe2O4 films annealed between 450 and 750 °C were textured polycrystalline with an epitaxial interfacial layer, which allows strain-mediated tuning of the magnetic properties given its highly magnetostrictive nature. The magnetic behavior was studied as a function of film thickness and annealing temperature: saturation magnetization (Ms) ranged from 260 to 550 emu/cm3 and magnetic coercivity (Hc) ranged from 0.2 to 2.2 kOe. Enhanced magnetic anisotropy was achieved in the thinner samples, whereas the overall magnetic strength improved after annealing at higher temperatures. The RE-ALD CoFe2O4 thin films exhibit magnetic properties that are comparable to both bulk crystal and films grown by other deposition methods, with thickness as low as ∼7 nm, demonstrating the potential of RE-ALD for the synthesis of high-quality magnetic oxides with large-scale processing compatibility.

Ferroelectric and Magnetic Properties of CoFe 2 O 4/BaTiO 3 Prepared by Microwave-Assisted Sol-Gel Method

The xCoFe 2O4/(1 −x)BaTiO 3 (x= 0.1 ∼ 0.5) multiferroic composites were prepared by microwave-assisted sol-gel method. The theoretical densities and actual densities of CoFe 2O4/BaTiO 3 were compared. The structural, ferroelectric, and magnetic properties were studied. At room temperature, the multiferroic composites exhibited good ferroelectric and magnetic properties. The maximum polarization 2.52 μC/cm 2 was obtained at x= 0.1 and the minimum polarization 1.21 μC/cm 2 was achieved at x= 0.5. The maximum saturation magnetization 35.020 emu/g and remnant magnetization 15.587 emu/g were obtained at x= 0.5.

Erratum to: Structural and Magnetic Properties of CoFe 2−x Gd x O4(0.0 ≤ x ≥ 0.1) Spinel Ferrite Nanoparticles Synthesized by Starch-Assisted Sol-Gel Auto-combustion Method

Acknowledgment This work was supported by Project Excellent Teams (CZ.1.07/2.3.00/30.0005) and Sustainability and Development, REG LO1211, National Programme for Sustainability I (Ministry of Education, Youth and Sports) at the Materials Research Centre, Brno University of Technology, and Project Centre of Polymer Systems (Reg. Number: CZ.1.05/2.1.00/03.0111) at Tomas Bata University in Zlin, Czech Republic.

Effects of Ultrasonic Agitation on the Structural and Magnetic Properties of CoFe2O4 Nanocrystals

AbstractCobalt ferrite nanocrystals (CoFe2O4) were synthesized by means of ultrasonic agitation and afterward subjected to different annealing temperatures. The structural and morphological properties of the nanocrystals were investigated by means of X‐ray diffraction and scanning electron microscopy. The results showed that the samples were composed of CoFe2O4 monophase nanocrystals. The particle size increased with increasing annealing temperatures. Infrared spectroscopy and magnetization showed that the samples exhibited the usual features of CoFe2O4 nanocrystals. Superparamagnetism was not observed at room temperature. However, the results indicated that the samples could be considered single‐domain particles with blocking temperatures greater than 300 K. Both infrared and magnetic results indicated possible diffusion of cobalt ions from tetrahedral to octahedral sites as a function of the annealing temperature.

Magnetic CoFe2O4/carbon nanotubes composites: fabrication, microstructure and magnetic response

By combining the unique microstructure of carbon nanotubes (CNTs) with the good magnetism of CoFe 2 O 4 ferrites, CoFe 2 O 4/CNTs nanocomposites were prepared by the solvothermal method for the application of targeting therapy and tumor hyperthermia. X-ray diffraction (XRD), thermal gravity analysis (TGA), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) were introduced to study the influence of the solvothermal temperature, time and the CNTs content on the microstructure and magnetic properties of CoFe 2 O 4/CNTs nanocomposites. The diameter of CoFe 2 O 4 nanoparticles coating on the surface of CNTs and the saturation magnetization (Ms) increased with the solvothermal temperature. CoFe 2 O 4/CNTs nanocomposites prepared at 180°C, 200°C and 220°C exhibited superparamagnetism at room temperature, while the samples prepared at 240°C and 260°C presented ferromagnetism. And the solvothermal time and CNTs content slightly affected the microstructure and magnetic properties, Ms and coercivity (Hc) increased slightly with the increasing solvothermal time and the decreasing CNTs content.

XPS and Magnetic Properties of CoFe<sub>2</sub>O<sub>4</sub> Nanoparticles Synthesized by a Polyacrylamide Gel Route

Cobalt ferrite CoFe2O4 nanoparticles were prepared via a polyacrylamide gel route and were characterized by XRD, SEM, XPS and VSM. It is demonstrated that the sample (designated S1) prepared without using the cross-linking agent bis-acrylamide has an average grain size of 45nm, while the sample (designated S2) prepared by introducing an amount of bis-acrylamide which is about 1/5 times the amount of acrylamide has an average grain size of 23nm. The two kinds of particles are shaped like spheres. The cation distribution is determined, from Co 2p3/2 and Fe 2p3/2 XPS spectra, to be (Co0.4Fe0.6)[Co0.6Fe1.4]O4 for both the samples, where (Co0.4Fe0.6) and [Co0.6Fe1.4] represent cations in the tetrahedral and octahedral sites, respectively. Magnetic measurement reveals a saturation magnetization of 67.3A·m 2 ·kg ¹1 for sample S1 and 62.3A·m 2 ·kg ¹1 for sample S2, but a similar coercivity of about 87.5kA·m ¹1 for both the samples. [doi:10.2320/matertrans.M2012151]

Effect of High Magnetic Field Annealing on Magnetic Properties of CoFe$_{2}$O$_{4}$ Nanowire Arrays

Cobalt ferrite (CoFe2O4) nanowire arrays with different diameters were prepared in porous anodic aluminum oxide (AAO) template by a sol-gel template method. A magnetic field annealing procedure was performed in the direction along wire axis (out of sample planes) at 600°C under 10-T applied magnetic field to orient the spinel CoFe2O4 crystalline. The morphology was studied by scanning electron and transmission electron microscope. X-ray diffraction (XRD) patterns show that samples performed by the magnetic field annealing procedure have a 〈110〉 texture along the nanowire axis, while those annealed without applied magnetic field show a nonoriented polycrystalline phase of spinel type structure. Vibration sample magnetometer (VSM) test shows the difference between CoFe2O4 nanowire arrays samples annealed with or without applied magnetic field. This difference shows the magneto-crystalline anisotropy with the easy magnetization direction along the nanowire axis, and is caused by the resultant effect of the easy magnetization direction distribution of the crystalline.

Controlling the electronic structure of Co1−xFe2+xO4thin films through iron doping

The electronic, magnetic and transport properties of iron-doped cobalt ferrite (Co${}_{1\ensuremath{-}x}{\mathrm{Fe}}_{2+x}$O${}_{4}$) thin films grown epitaxially on MgO (001) substrates are investigated by soft x-ray absorption and photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, superconducting quantum interference device magnetometry, and resistivity measurements. The crystal structure for Co${}_{1\ensuremath{-}x}$Fe${}_{2+x}$O${}_{4}$ is determined to be nearly inverse spinel, with the degree of inversion increasing for increased doping until it becomes fully inverse spinel for Fe${}_{3}$O${}_{4}$. The doped iron cations have a valency of 2$+$ and reside solely on octahedral sites, which allows for conduction owing to hopping between Fe${}^{2+}$ and Fe${}^{3+}$ octahedral cations. The addition of Fe${}^{2+}$ cations increases the electron density of states near the Fermi energy, shifting the Fermi level from 0.75 to 0 eV with respect to the top of the valence band, as the doping increases from $x$ $=$ 0.01 to 1. This change in electronic structure results in a change in resistivity by over two orders of magnitude. In contrast, the magnetic properties of CoFe${}_{2}$O${}_{4}$ thin films, characterized by a significantly reduced saturation magnetization compared to the bulk and large magnetic anisotropies, are affected less significantly by doping in the range from 0 to 0.63. These results show that Co${}_{1\ensuremath{-}x}$Fe${}_{2+x}$O${}_{4}$ has tunable electronic properties while maintaining magnetic properties similar to CoFe${}_{2}$O${}_{4}$.

The Effect of Surface Modification on the Magnetic Properties of CoFe2O4 Nano-Particles Synthesized by the Hydrothermal Method

Cobalt ferrite (CoFe2O4) nano-particles were synthesized by the hydrothermal method with the addition of a surfactant sodium bis(2-ethylhexyl) sulphosuccinate (AOT). Characterization measurements including X-ray diffraction, transmission electron microscopy and Fourier transform infrared spectroscopy showed that all the final products were single-phase CoFe2O4 nano-crystals with AOT molecules bonding to the surfaces, the average crystallite sizes were all near 25 nm, and the lattice constant increased with the increasing mass of AOT. The magnetic hysteresis loops measured at room temperature indicated that the bonding of the AOT to the surfaces led to an increase of the saturation magnetization (Ms), the coercivity (Hc) and the remanence ratio (Mr/Ms). Furthermore, as the concentration of AOT reached the critical micelle concentration (CMC), turning points were observed in the the curves of Hc, Mr/Ms and K(eff) (effective magnetic anisotropy constants) versus. the mass of AOT due to the formation of the AOT micelles.

SSG or SFM state in [formula omitted] nano-agglomerates fabricated by micro-emulsion method

We report on magnetic properties of CoFe 2 O 4 nano-agglomerates obtained by micro-emulsion technique under specific conditions. The samples form a unique morphology as observed by transmission electron microscopy and scanning electron microscopy investigations. Concerning magnetic properties, they exhibit a considerable coercivity of almost 1 T at 2 K, which continuously decreases up to the characteristic temperature, T g = 350 K . The temperature dependence of the zero-field cooled (ZFC) and field cooled (FC) magnetization, respectively, is furcated at the T g , and the temperature dependencies of the a.c. susceptibility exhibit a frequency-dependent maximum at ∼ T g . The observed behavior is discussed in terms of the super-spin-glass (SSG) and the super-ferromagnetic (SFM) regime considering the morphology of the nano-agglomerates.

Magnetic properties of CoFe 1.9RE 0.1O 4 nanoparticles (RE=La, Ce, Nd, Sm, Eu, Gd, Tb, Ho) prepared in polyol

Highly crystalline CoFe 1.9RE 0.1O 4 ferrite nanoparticles, where RE=La, Ce, Nd, Sm, Eu, Gd, Tb, and Ho, have been synthesized by forced hydrolysis in polyol. X-ray diffraction (XRD), transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), 57Fe Mössbauer spectrometry, Co K-edge X-ray absorption spectroscopy and magnetic measurements using a SQUID magnetometer were employed to investigate the effect of the substitution RE 3+ ions for Fe 3+ ones on the structure, the microstructure, the chemical homogeneity, and the magnetic properties of the cobalt ferrite system. All the produced particles are superparamagnetic at room temperature. Nevertheless, the substitution causes reduction of the blocking temperature which is mainly ascribed to partial cation exchange among the spinel-like sublattices of CoFe 2O 4 induced by the insertion of the relatively large RE 3+ ions. The low-temperature saturation magnetization and coercivity appear to be greatly affected by the nature of RE 3+ ions—maxima values were found for Gd 3+ and Eu 3+, respectively.

Effects of an Os layer on the magnetic properties of CoFe∕IrMn

The uses of Os as an antidiffusion and buffer layer in IrMn exchange coupled CoFe film were investigated. For the purpose of antidiffusion, the inserted Os layer showed a distinct improvement of S>0.9, with HC slightly increasing by 1.6 times for the CoFe∕Os∕MnOs multilayer after 400 °C annealing, even though the Os thickness was as thin as 0.3 nm. Furthermore, with a 0.3 nm Os barrier, the 350 °C annealed CoFe∕Os∕IrMn∕CoFe showed almost the same magnetic behavior as the as-deposited state, while the Hex of the upper part of the CoFe∕Os∕IrMn changed from 100 to 190 Oe. In addition, as a buffer layer, the Os buffer layer could enhance the diffraction peak intensities of IrMn(111)∕Os(002) and CoFe (111), and the Hex of CoFe∕IrMn was proportional to the Os thickness. A 120 Oe of Hex was achieved by using an 11 nm Os buffer layer in a CoFe10nm∕IrMn15nm bottom type film. These results show that Os has the potential to be an antidiffusion and buffer layer in a magnetic multilayer.

Structural and magnetic properties of CoFe 1.9RE 0.1O 4 (RE=Y, La) prepared by a sol–gel method

Ultrafine CoFe 1.9RE 0.1O 4 (RE=Y, La) powders have been fabricated by a sol–gel method. Structural and magnetic properties of the powders were investigated by X-ray diffractometer, Mössbauer spectroscopy, and vibrating sample magnetometer. The CoFe 1.9Y 0.1O 4 powders that were fired at and above 923 K contained only a single spinel phase and behaved ferrimagnetically. Powders fired at 723–823 K had a spinel structure and were mixed paramagnetic and ferrimagnetic in nature. Mössbauer spectra of the CoFe 1.9Y 0.1O 4 powder fired at 923 K were taken at various temperatures ranging from 18 to 865 K. The iron ions at both A (tetrahedral) and B (octahedral) sites were found to be in ferric high-spin states. The Néel temperature T N was found to be 865±2 K. Debye temperatures for A and B sites were found to be Θ A=695±5 K and Θ B=279±5 K, respectively. The magnetic behaviors of the CoFe 1.9Y 0.1O 4 powders fired at and above 1123 K and CoFe 1.9La 0.1O 4 powders fired at and above 923 K, respectively, showed that an increase of the firing temperature yielded a decrease in the coercivity and an increase in the saturation magnetization. The maximum coercivity and the saturation magnetization were H c=1208 Oe and M s=69 emu/g in the CoFe 1.9Y 0.1O 4 samples and H c=703 Oe and M s=72 emu/g in the CoFe 1.9La 0.1O 4 samples.

The effects of buffer layers on the crystalline structures and magnetic properties of Co-rich Co-Fe and Co-Fe-Al films

The crystalline structures and magnetic properties of Co-Fe and Co-Fe-Al films with various buffer layers (Cu, Permalloy and Zr), grown on glass or Si substrates, have been studied. It was found that the Co-Fe films on Zr underlayers exhibit very good FCC (111) orientation parallel to the film plane, whereas neither Cu nor Permalloy can suppress the intrusion of HCP phase in the Co-Fe films. Furthermore, the FCC (111) orientation is greatly enhanced by adding a small amount of Al to the Co-Fe films with Zr underlayers. The magnetic softness expected for the films with (111) orientation of the FCC phase was not attained for the Co-Fe films because of residual HCP phase and deterioration of the (111) orientation by annealing. On the other hand, the Co-Fe-Al films with Zr buffer layers, which have a single FCC phase with enhanced (111) orientation, are magnetically soft.