Fabrication and magnetic properties of Fe<Subscript>3</Subscript>Co<Subscript>7</Subscript> alloy nanowire arrays

Fe₃Co₇ alloy nanowire arrays have been fabricated by direct current electrodeposition of Fe²⁺ and Co²⁺ into anodic aluminum oxide (AAO) templates. The phase structure and magnetic properties of the nanowires were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). Magnetic measurements show that the coercivity and remanence of the as-deposited Fe₃Co₇ Alloy nanowires increase dramatically after heat-treatment at 773 K for 2 h, and the nanowire arrays exhibit uniaxial magnetic anisotropy with easy magnetization direction along the nanowire axes owing to the large shape anisotropy. The great difference between practical coercivity and ideal coercivity was also discussed in detail.     

Structural and magnetic properties of Co and Co71Ni29 nanowire arrays prepared by template electrodeposition

A comparative study on the structural and magnetic properties of Co and Co₇₁Ni₂₉ nanowire arrays prepared by AC electrodeposition in alumina templates has been presented. The Co and Co₇₁Ni₂₉ nanowires observed by SEM and TEM have a 45 nm diameter and exhibit high aspect ratio. Also, the nanowires of both Co and Co₇₁Ni₂₉, determined by XRD, have an identical crystallographic structure. The Co₇₁Ni₂₉ nanowires exist in a cobalt solid solution. Both the as-obtained Co and Co₇₁Ni₂₉ nanowire arrays measured by VSM show obvious magnetic anisotropy, dominated by shape anisotropy. Compared to the Co nanowire arrays, Co₇₁Ni₂₉ nanowire array shows an enhanced coercivity Hc (⊥) and approximate square ratio Mr/Ms(⊥).     

Electrochemical fabrication and magnetic properties of Fe<Subscript>7</Subscript>Co<Subscript>3</Subscript> alloy nanowire array

A new type of magnetic material, Fe₇Co₃ nanowires, was successfully synthesized for the first time via a simple electrodeposition method. Highly uniform, self-ordered porous anodic aluminum oxide (AAO) membranes were prepared by the way of electrochemical. Fe₇Co₃ alloy nanowire arrays were fabricated in the porous alumina template in an aqueous solution of FeCl₂ and CoCl₂ by direct current electrodepositing. The microstructures of nanowires and AAO template were characterized by XRD, SEM, and TEM. The results show that a single Fe₇Co₃ nanowire is 40 nm in width and 2.5 μm in length with a preferred crystal face (110) during growing. The Fe₇Co₃ nanowire arrays have uniaxial magnetic anisotropy with easy magnetization direction along the nanowire axis due to the large shape anisotropy. It also shows that Fe₇Co₃ nanowire is a well-soft magnetic phase compared with Fe nanowires. It illustrates that Fe₇Co₃ possess higher saturation magnetization.     

Hydrothermal synthesis and magnetic properties of CoxFe1−x/CoyLazFe3−y−zO4 composites

A series of iron–cobalt alloy and cobalt–ferrite composites doped with La³⁺ (Co_xFe_1−x/Co_yLa_zFe_3−y−zO₄) in which the Fe–Co alloy has either a bcc or a fcc structure and the oxide is a spinel phase, have been synthesized by using the disproportionation of Fe (OH)₂ and the reduction of Co (II) by Fe⁰ in a concentrated and hot KOH solution. when x ≤ 0.1, the structures of the Fe_xCo_1−x alloy and cobalt–ferrite are fcc structure; and when x ≥ 0.25, the structures of the Fe_xCo_1−x alloy is bcc structure. The fcc structure of alloy is favored for [KOH] close to 9 N, Co(II)/Fe(II) ratios between 0.5 and 0.9 and short reaction time of synthesis. And the bcc structure of the alloy is favored for [KOH] close to 1 N, Co(II)/Fe(II) ratios between 0.1 and 0.5 and long reaction time of synthesis. A low [KOH] favors nucleation leading to octahedral of 1 μm. And [KOH] of 9–12 N favors particle growth. The metal occurs in square particles of 100–150 nm included within the spinel. Powder X-ray diffraction (XRD), thermal gravity analysis (TGA) and different thermal analysis (DTA), scanning electron microscope (SEM), transmission electron micrograph (TEM) and vibrating sample magnetometer (VSM) were employed characterize the crystallite sizes, structure, morphology and magnetic properties of the composites. And the effect of the Co(II)/Fe (II) ratio (0 ≤ Co/Fe ≤ 1), concentration of KOH, reaction time and substitution Fe³⁺ ions by La³⁺ ions on structure, magnetic properties of the composites were investigated.     

The influence of alloying Fe<Subscript>59</Subscript>Pt<Subscript>41</Subscript> thin films with Co on their magnetic and microstructural properties

This study investigates how the addition of Co to a Fe₅₉Pt₄₁ alloy with compositions in the range of Fe₅₉Pt₄₁–Co₅₉Pt₄₁ affects the crystallographic ordering temperatures and magnetic properties of sputter-deposited films. Introducing Co into the (Fe_1−x Co _x )₅₉Pt₄₁ film affects the activation energy of atomic migration and grain growth, thus leading to a higher annealing temperature of the L1₀ phase formation. At a Co concentration of x = 0.2, the saturation magnetization was maximum, at 1,480 emu/cm³, and the (Fe_0.8Co_0.2)₅₉Pt₄₁ film exhibited a coercivity of about 4 kOe.     

Effect of composition on the crystallization and magnetic properties of Fe–Co–Si–B–Nb amorphous alloys

The crystallization behavior and magnetic properties of Fe₆₂Co₁₀Si_15−x B_18−y Nb_{(x + y)−5} amorphous alloys with x = 0–5 and y = 0–5 were examined. Primary crystallization temperature of Fe₆₂Co₁₀Si_15−x B₁₃Nb _x and Fe₆₂Co₁₀Si₁₀B_18−y Nb _y alloys increased with the addition of Nb. The primary and secondary crystallization temperatures were well separated when the Nb content is above 4 at%. The alloys with 15–18 at% B showed a distinct supercooled region. The Nb addition decreased the Curie temperature as well as room temperature saturation magnetization. The glassy-type Fe₆₂Co₁₀Si₁₀B₁₈ alloy exhibited good soft magnetic properties as well as a supercooled liquid region of 39 K. The finding of the glassy-type Fe-based alloy without Nb element exhibiting high Bs above 1.4 T is promising for future use as a soft magnetic glass material.     

Electrical and Magnetic Properties of Zr4+ and Ni2+ Ions Substituted Mn–Cu Spinel Ferrites

The Mn–Cu nanoferrites of composition Mn_0.5Cu_0.5Fe_2−2x Ni _x Zr _x O₄ (0.00≤x≤0.80) were synthesized by incorporating dopant Zr⁴⁺ and Ni²⁺ cations via a chemical coprecipitation technique. The single phase of the prepared spinel nanoferrites with particle sizes 15–31 nm was confirmed by XRD. Both electrical and magnetic properties are found to depend on the x contents and explained by considering the Zr⁴⁺ and Ni²⁺ cations distribution, displacement of the Fe³⁺ ions by dopants, changes in magnetic moment at tetrahedral A site and octahedral B site, Fe³⁺(A)–O₂–Fe³⁺ [B] linkages and extent of the primary superexchange interactions (A)–O–[B] of the Fe³⁺ ions on the A and B-sites. DC resistivity, saturation magnetization (M _s), remanence (M _r) and Bohr magneton (n _B) are observed to increase up to x≤0.40, while these parameters fall at relatively higher value of x≥0.60.     

The synthesis and the magnetic properties of Sm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BiY<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>5</Subscript>O<Subscript>12 </Subscript>nanoparticles

Sm _x BiY_2–x Fe₅O₁₂ (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8) nanocrystals were fabricated by sol–gel method. Samples were characterized by powder X-ray diffraction (XRD), thermal gravity analysis (TGA) and differential thermal analysis (DTA), transmission electron microscopy (TEM), vibrating sample magnetometer(VSM). The samples were calcined at 850 °C and 1000 °C and the average size of the particles were determined by Scherrer’s formula . In this paper, we discussed the effect of Sm³⁺ substitution for Y³⁺ on magnetic properties of BiY₂Fe₅O₁₂. The magnetic properties of Sm _x BiY_2−x Fe₅O₁₂ are decreased with increasing content of Sm ion.     

Effect of the Electrodeposition Frequency,Wave Form,and Thermal Annealing on Magnetic Properties of [Co0.975Cr0.025]0.99Cu0.01 Nanowire Arrays

Highly ordered [Co _0.975Cr _0.025]_0.99Cu _0.01 nanowire arrays were electrodeposited by conducting alternating current (AC) conditions from sulfate-based electrolyte into nanopores of anodic aluminum oxide (AAO) template with 37 nm pore diameter and the interpore distances of almost 50 nm. Fabricated nanowire arrays were characterized using scanning electron microscopy, alternating gradient force magnetometer, and X-ray diffraction. The results illustrated that varying frequency, wave form, and annealing procedure had influence on magnetic properties of as deposited nanowires. The nanowire arrays electrodeposited at different electrodeposition frequencies show remarkably different magnetic behaviors. Due to increasing of the electrodeposition frequency, the rate of ions for reduction was decreased. The nanowires prepared at various wave form illustrated insignificant impact on magnetic properties. X-ray diffraction patterns display that both as-deposited and annealed nanowire arrays expose the same structure. The raised value of coercivity has been determined in annealed nanowire arrays. Magnetization measurements show that the maximum value of coercivity for [Co _0.975]_0.99Cu _0.01 nanowires is observed at high temperature.     

Non-equilibrium crystallization diagram for the Co75.26−xFe4.74(BSi)20+x amorphous metal alloys

A non-equilibrium crystallization diagram for Co sub-surface layers of the Co_75.26–x Fe_4.74(BSi)_20+x amorphous alloy for x > 1 during magnetic field annealing is determined using Transmission Electron Microscopy (TEM). The diagram shows that, depending on the composition and temperature, the Co sub-layer exhibits five distinctively different microstructures when the metallic glass is heat treated below its bulk crystallization temperature. At high boron content, the structure is dominated by the FCC structure with a high degree of oxygen impurity faulting regardless of the annealing temperature. At low concentration, the Co sub-layer exhibits FCC or HCP structures, depending on the temperature. Also found was a two-phase region in which FCC and HCP Co co-existed. Such a diagram serves as a useful guide to obtaining the desired properties as the microstructure is closely linked to the magnetic properties of the material.     

Electrical conductivity of LaCoxFe1 ? xO3 ? δ and LaLi0.1CoxFe0.9 ? xO3 ? δ (0 ≤ x ≤ 0.4) oxides

We have studied the effect of Co and Li concentrations on the phase composition and electrical conductivity of LaCo _x Fe_{1 − x} O_{3 − δ} and LaLi_0.1Co _x Fe_{0.9 − x} O_{3 − δ} perovskite-like oxides synthesized in air at 1470 K. Single-phase materials with an orthorhombic crystal structure were obtained in the range 0 ≤ x ≤ 0.3. The composition dependences of conductivity have a minimum at x _c = 0.1 and 0.2, respectively. In the range x > 0.1, the conductivity of LaCo _x Fe_{1 − x} O_{3 − δ} increases with increasing Co concentration for T > 700 K and decreases for T < 600 K. The conductivity of La(Li_0.1Co _x Fe_{0.9 − x} )O_{3 − δ} in the range 0 ≤ x ≤ 0.1 and for x ≥ 0.2 increases with Co concentration throughout the temperature range studied.     

Magnetic properties of Bi(Fe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>M<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)O<Subscript>3</Subscript> (M = Mn,Ti)

The magnetic properties of Bi(Fe_{1 − x} M _x )O₃(M = Mn, Ti) solid solutions have been studied in magnetic fields of up to 11.2 × 10³ kA/m, and the composition stability range of the R3c ferroelectric phase has been determined. The results indicate that partial Ti⁴⁺ substitution for Fe³⁺ leads to a transition from a modulated antiferromagnetic state to a homogeneous weakly ferromagnetic ferroelectric state (x = 0.08), whereas the Bi(Fe_1−x ³⁺Mn _x ³⁺)O₃ solid solutions do not exhibit weak ferromagnetism. Charge compensation in is assumed to be ensured by cation vacancies.     

Transport,magnetic and spectroscopic studies of nickel-gallium ferrites

X-ray, electrical conductivity, magnetic hysteresis and infrared spectroscopic studies for the system NiGa_2−2xFe_2xO₄ were carried out. All the compounds, 0 x⩽1 showed cubic symmetry. The activation energy, thermoelectric coefficient values decreased with increasing Fe³⁺ concentrations but with increasing number of Fe³⁺ ions, the values of lattice constant and magnetic moment increased. Compounds with x⩽0.5 are p-type while those with x⩾0.75 are n-type semiconductors. Magnetic hysteresis loops indicated that the compounds with x⩾0.25 are ferrimagnetic while the compound NiGa₂O₄ (x=0.0) is anti-ferromagnetic. Constant and low values of coercive force indicated that the compounds with x⩾0.50 exhibit multidomain behaviour. X-ray intensity calculations, electrical conductivity, magnetic hysteresis and infrared studies indicate the presence of Ga³⁺ ions at the tetrahedral site, Ni²⁺ ions at the octahedral site and Fe³⁺ ions are present in both tetrahedral and octahedral sites. The probable ionic configuration for the system NiGa_2−2xFe_2x O₄ is suggested to be Ga _1−x ³⁺ Fe _x ³⁺ [Ni²⁺ Fe³⁺ O ₄ ²⁻ .     

Effect of cobalt substitution on magnetic and transport properties of Nd0·5Sr0·5Mn1?xCoxO3 (x = 0·1, 0·3 and 0·5)

The magnetic and transport properties of the compounds Nd_0·5Sr_0·5Mn_1-x_{{\rm 1}-{x}}Co_x_{{x}}O₃ (x = 0·1, 0·3 and 0·5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The double exchange interaction is stronger between Mn^3 +–O^2 −–Mn^4 + as compared to Co^3 +–O^2 −–Co^4 + pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting features due to localization of charge carriers (mobile e_g{e}_{\rm g} electrons).     

Observation of the Onset of Magnetic Clustering in Superparamagnetic Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O Films

A series of high quality Zn_1−x Co _x O thin films were obtained by UHV-magnetron reactive sputtering. Detailed X-ray diffraction, X-ray absorption near edge spectra, and X-ray linear dichroism measurements were used for analyzing the long- and short-range crystalline structure, respectively. These techniques reveal excellent crystalline ordering on both scales for films with oxygen-rich conditions and indicate that Co²⁺ ions are located on substitutional Zn sites without detectable phase separation. Interestingly, decreasing the structural quality of such Zn_1−x Co _x O films leads to altered magnetic properties as measured by SQUID magnetometry, ranging from paramagnetism to the emergence of magnetic clustering exhibited by superparamagnetism. In some cases, a small shift of the hysteresis loop is visible after field cooling indicating weak exchange bias typical for the AFM/FM (CoO/Co) system. In the light of detailed structural investigations, the transition regime from paramagnetic to superparamagnetic behavior is discussed.     

From Magnetite to Cobalt Ferrite

We synthesized Fe_3–x Co _x O₄ (x = 0–1) using the hydrothermal method in order to demonstrate the compositional modulation of magnetite to cobalt ferrite. Our Mössbauer spectroscopy results provided direct evidence for the presence of the Co substitution in the B sublattice, which was found to be accompanied by a systematic increase of the hyperfine magnetic field at these sites. The mechanism we propose relies on the substitution of Fe²⁺ by Co²⁺ in the B sublattice and is supported by the observed dependence of the populations of the (A) and (B) sites on content x of cobalt substitution. The X-ray diffraction (XRD) determinations demonstrated a linear increase in the lattice parameter when going from magnetite to cobalt ferrite. For the particular value x = 0.1, we report that the two sublattices of magnetite become equally populated with Fe. For this particular value of the cobalt content, we obtained a thin film sample by laser ablation deposition and characterized its properties by XRD and conversion electron Mössbauer spectroscopy (CEMS).     

Effect of iron doping on magnetic properties of Sr0.78Y0.22CoO2.625+δ-layered perovskite

The Sr_0.78Y_0.22Co_1−x Fe _x O_2.625+δ (x = 0 and 0.12) system has been studied using neutron diffraction technique, magnetization, and elastic properties measurements. Undoped sample exhibits superstructure with 2√2a _p  * 2√2a _p  * 4a _p metrics and structural phase transition at T = 360 K. Magnetic ordering starts to develop below 360 K. Spontaneous magnetization shows anomalous behavior and reaches maximal value nearly room temperature. A magnetic structure of the both compounds has been described assuming G-type antiferromagnetic ordering. There are two different magnetic moment values for Co ions in CoO₆ and CoO_4.5 layers. Magnetic moments in CoO_4.5 layers are larger than those for octahedrons. The refined values of magnetic moments indicate a mixed low–high spin state of Co³⁺ for the both layers. There is no evidence for any change of the magnetic structure type with temperature lowering despite the anomalous magnetization behavior. Iron doping (x = 0.12) leads to a suppression of the small ferromagnetic component, disappearance of the 2√2a _p  * 2√2a _p  * 4a _p metrics, and strong increase of the average magnetic moment for Co_4.5 layer. It is suggested that the ferromagnetic component in the undoped samples is a result of non-collinearity of the magnetic moments within CoO_4.5 layers.     

Dominancy of antiferromagnetism in Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O diluted magnetic semiconductors

The outline of magnetic interactions in DMSs was determined using Zn_1−x Co _x O particles, where “x” was changed as 0.01, 0.05, 0.10, 0.15, and 0.20. The syntheses were accomplished though mechanical milling and thermal treatment, known as solid state reaction. The formation of each synthesis was monitored by differential thermal and thermo gravimetric methods (DT-TGA). Substitution of Co²⁺ ions with Zn²⁺ host atoms in a ZnO lattice was analyzed using X-ray diffraction (XRD) patterns, Fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray spectrometry (EDS) data, transmission electron microscopy (TEM) figures, scanning area electron diffraction (SAED) patterns, and X-ray photo spectroscopy (XPS) spectrum. The measured Co contents in ZnO lattice were found to be ~0.7% less than the expected result. In addition to Zn_1−x Co _x O particles, tungsten (W) contaminations were noticed in the variations of 1.5 ± 0.2%, as originating from the abrasion between the miller and balls. The progressive replacement of Co²⁺ with Zn²⁺ host ions in ZnO lattice from 1% to 20% decreased the band edge from 3.03 ± 0.01 eV to 2.95 ± 0.01 eV, respectively. Co doping has also changed the magnetic nature of the ZnO. Although having both interactions (ferromagnetic and antiferromagnetic), dominance of ferromagnetic behavior was only observed for Zn_0.99Co_0.01O with the coercivity of ~154 ± 50 Oe and positive Curie–Weiss temperature as 79 ± 1 K. However, the calculated \frac2J_\textex k_\textB {\frac{{2J_{\text{ex}} }}{{k_{\text{B}} }}} values have proved that the higher Co²⁺ concentrations in ZnO lattice have increased the efficiency of antiferromagnetic interactions. Surprisingly, there was no rapid change at \frac2J_\textex k_\textB {\frac{{2J_{\text{ex}} }}{{k_{\text{B}} }}} values as mentioned in previous works.     

Oxygen condensation stacking faults in crystallized Co found during magnetic annealing of Co-rich amorphous alloy

Amorphous Co_75.26–x Fe_4.74(BSi)_20+x (0 < x) magnetic alloys were examined with Transmission Electron Microscopy (TEM) after magnetic field annealing. TEM analysis revealed that the crystallized Co layer under the surface oxide could be highly faulted with planar defects depending on the composition. Based on the electron diffraction, we have proposed a new form of stacking fault in which two oxygen atoms are substituted for FCC Co in the {111} planes to create randomly distributed clusters of oxygen atoms on the Co {111} planes. Such clusters would explain the absent {200} peak in the highly faulted composition of crystallized FCC Co and the streaks observed in the electron diffraction pattern of the material. The oxygen fault was also closely related to the magnitude of the induced magnetic anisotropy of the material, suggesting the Co–O bonds acting as the localized antiferromagnetic region.     

Synthesis and Properties Investigation of Non-equivalent Substituted W-Type Hexaferrite

A novel composed W-type hexaferrite Ba_1?x La _x Co₂Fe₁₆O₂₇ was rapidly synthesized via a sol–gel self-combustion reaction. The effects of lanthanum ions on the oxidation state of iron ions and cobalt ions in hexaferrite were explored by X-ray photoelectron spectroscopy. The changes of the Fe 2p X-ray absorption spectra indicated that the nonequivalent substitution can lead to the transition Fe³⁺→ Fe²⁺ in Ba_1?x La _x Co₂Fe₁₆O₂₇. However, the oxidation state of cobalt ions was maintained as Co²⁺. Moreover, the effects of La content on the phase composition, structural parameters, morphology, and static magnetic properties were also investigated in detail by using the X-ray diffractometer, scanning electron microscope, and vibrating sample magnetometer. The results indicated that the structural parameters decreased regularly with increasing the La content, and the magnetic properties were enhanced after substitution, which is beneficial for their application in various electrical devices employed for industrial and military applications.