Effects of layering and magnetic annealing on the texture of CoPt films

The effect of magnetic field annealing of magnetron sputtered CoPt alloy films and Co/Pt bilayers on the crystallographic texture of the obtained chemically ordered (L1₀) CoPt films is presented. In CoPt alloy films the main effect of the magnetic field is to suppress (1 1 1) growth in the early stages of L1₀ formation whereas the development of (0 0 1) versus (1 0 0) texture is related to chemical ordering strain. A higher degree of (0 0 1) texture is obtained by magnetically annealing Co/Pt bilayers since the initial (1 1 1) texture in the as-sputtered films is avoided and Co-Pt alloying occurs in the presence of the magnetic field.     

Effect of magnetic field annealing on microstructure and magnetic properties of FePt films

FePt (20 nm) films were annealed in a magnetic field (along the normal direction of the films) at a temperature around the Curie temperature of L1₀ FePt. The influence of magnetic filed annealing on texture and magnetic properties of FePt films were investigated. The results indicate that preferential (0 0 1) orientation and perpendicular anisotropy can be obtained in L1₀ FePt films by using magnetic field annealing around the Curie temperature of L1₀ FePt. This is one of the potential methods to obtain (0 0 1) orientation and thus to improve the perpendicular anisotropy in FePt films.     

Effect of high magnetic field annealing on the microstructure and magnetic properties of Co-Fe layered double hydroxide

The effects of high magnetic field (10 T) on the products obtained by calcination of Co-Fe LDH precursors at different temperatures were investigated. The XRD results indicated that Fe^III substituted for Co^III in Co₃O₄ to yield Co^IICo^IIIFe^IIIO₄ under the calcination of Co-Fe LDH precursors at 400 °C. The products obtained by magnetic field annealing at 400 °C had a porous plate-like morphology, whereas the products without magnetic field annealing were composed of nanoparticles. It was seen that CoFe₂O₄ phase could be formed at low temperature (about 500 °C) under the magnetic field annealing. The grain size of products obtained by magnetic field annealing at 800 °C was larger than that of zero magnetic field. It was found that the saturation magnetization was significantly enhanced after magnetic field annealing, especially at lower temperature (≤600 °C). The possible reason for the effects on the microstructure and magnetic properties of products obtained by magnetic field annealing was discussed.     

Effect of magnetic annealing on phonon behaviors of nanocrystalline BiFeO3

Influence of magnetic annealing at 823 K up to 10 T (T) on the phonon behaviors of nanocrystalline BiFeO₃ was investigated by Raman spectroscopy. The frequencies of fundamental Raman modes increase obviously with increasing annealing magnetic field, and the intensity of the 1260 cm⁻¹ two-phonon mode decreases. The pronounced anomalies of Raman phonon modes under magnetic annealing are attributed to the change of the spin-phonon coupling due to the modulation of spiral spin order. Furthermore, the temperature dependence of Raman peak positions, for the two prominent modes (147 and 176 cm⁻¹), show no notable anomaly around T_N except the sample annealed under 10 T magnetic field; meanwhile, in this sample, another obvious phonon anomaly occurs at ∼150 K (another magnetic phase transition point), which indicate that stronger magnetic annealing with 10 T intensely enhances the spin-phonon coupling, and possibly increases magnetoelectric coupling of nanocrystalline BiFeO₃ due to severely modulation of spiral spin order.     

Developments in the production of grain-oriented electrical steel

The quality and production technology of grain-oriented electrical steel have been improved over the past 70 years. Firstly, through the improvement of {1 1 0} 〈0 0 1〉 alignment, development of thinner-gauge material, and establishment of magnetic domain refining techniques, magnetic properties of the material have been improved dramatically. Secondly, many mechanisms have been proposed for the reason why Goss texture develops selectively during the final annealing stage. Thirdly, to reduce manufacturing costs, many new techniques have been developed. The most advanced in commercial realization is the application of low-temperature slab-reheating techniques. Despite these achievements, the mechanisms of texture selection are not yet clear in all their details. Further improvement of magnetic properties and the application of compact production process for grain-oriented electrical steels in commercial production are needed to be realized.     

Magnetic field annealing effects on self-oriented BiFeO3 thin films prepared by chemical solution deposition

Self-oriented BiFeO₃ (BFO) thin films are prepared via chemical solution deposition method with magnetic field in-situ annealing process. The effects of magnetic annealing on the microstructure, magnetic and dielectric properties as well as magnetoelectric coupling effect of the BFO thin films are investigated. With increasing the annealing magnetic field, the crystallization quality, texture, grain boundary connectivity and densification of the films are enhanced, which is attributed to the improvement of connection and diffusion of components. The magnetization of the field-annealing films and dielectric constant as well as remanent polarization increases with increasing the strength of annealing magnetic field. In addition, it is observed that magnetocapacitance value of the magnetic-field-annealing BFO thin film is higher than the non-field-annealing one. Moreover the BFO thin films annealed at 3 kOe magnetic field show the magnetoelectric effect with 4% under 2 kOe at room temperature.     

Microstructure and magnetic properties of FePt:Ag nanocomposite films on SiO2/Si(1 0 0)

FePt:Ag nanocomposite films were prepared by pulsed filtered vacuum arc deposition system and subsequent rapid thermal annealing on SiO₂/Si(1 0 0) substrates. The microstructure and magnetic properties were investigated. A strong dependence of coercivity and ordering of the face-central tetragonal structure on both Ag concentration and annealing temperature was observed. With Ag concentration of 22% in atomic ratio, the coercivity got to 6.0 kOe with a grain size of 6.7 nm when annealing temperature was 400 °C.     

Dependence of microstructure and magnetic properties of FePt/B nanocomposite films on boron content

Compared with previous work, FePt/B nanocomposite films with larger B content in a wide range were prepared by magnetron sputtering plus subsequent annealing on Si (1 0 0) substrates. When the volume percentage is no less than 12%, both interstitial incorporation and intergranular segregation of the B are found, resulting an enlargement of the FePt lattice and a decrease of the FePt grain size. Effect of B content on magnetic properties, such as magnetization, switching field and exchange coupling of the FePt based films, is also discussed.     

Temperature dependence of the stability of written bits in a magnetic hard-disk medium investigated by magnetic force microscopy

The thermal stability of written bits in a magnetic hard-disk medium has been investigated with a magnetic force microscope (MFM), which was equipped with an in situ heating system capable of heating the medium up to 300 °C. It is shown that both the annealing temperature and the duration have significant effect on the decay of the MFM signal. No signal decay is observed when annealing for 30 min up to temperatures of 200 °C. The MFM signal decays rapidly with increasing temperature, for temperatures over 200 °C. Repeated annealing at 280 °C with a duration below 10 min does not cause any signal decay.     

Magnetic nanocomposite spinel and FeCo core-shell and mesoporous systems

The fabrication of condensed silica and mesoporous silica coated spinel CoFe₂O₄ and FeCo alloy magnetic nanocomposites are reported. The encapsulation of well-defined 5 nm thick uniform silica layer on CoFe₂O₄ magnetic nanoparticles was performed. The formation of mesopores in the shell was a consequence of removal of organic group of the precursor through annealing. The NiO nanoparticles were loaded into the mesoporous silica. The mesoporous silica shells leads to a larger coercivity than that of pure CoFe₂O₄ magnetic nanoparticles due to the decrease of interparticle interactions and magneto-elastic anisotropy. In addition, the FeCo nanoparticles were coated by condensed and mesoporous silica. The condensed silica can protect the reactive FeCo alloy from oxidation up to 300 °C. However, saturation magnetization of FeCo nanoparticles coated by silica after 400 °C annealing is dramatically decreased due to the oxidation of the FeCo core. The mesoporous silica coated magnetic nanostructure loaded with NiO as a final product could be used in the field of biomedical applications.     

Hydrothermal synthesis and Magnetocaloric effect of La0.5Ca0.3Sr0.2MnO3

The hydrothermal synthesis and magnetic entropy change for the perovskite manganite La_0.5Ca_0.3Sr_0.2MnO₃ have been studied. The La_0.5Ca_0.3Sr_0.2MnO₃ can be produced as phase-pure, crystalline powders in one step from solutions of metal salts in aqueous potassium hydroxide solution at a temperature of 513 K in 72 h. Scanning electron microscopy shows that the materials are made up of cuboid-shaped particles in typical dimension of 4.0×2.5×1.6 μm. Heat treatment can improve the magnetocaloric effect for the hydrothermal sample. The maximum magnetic entropy change ΔS_M for the as-prepared sample is 0.88 J kg⁻¹ K⁻¹ at 315 K for a magnetic field change of 2.0 T. It increases to 1.52 J kg⁻¹ K⁻¹, near its Curie temperature (317 K) by annealing the sample at 1473 K for 6 h. The hydrothermal synthesis method is a feasible route to prepare high-quality perovskite material for magnetic refrigeration application.     

Magnetization of epitaxial MnGe alloys on Ge(1 1 1) substrates

The structural and magnetic properties of an Mn rich solid phase epitaxy Mn_xGe_1−x alloy grown on a clean 2 × 8-Ge(1 1 1) surface, with a Curie temperature of about 300 K are investigated. Magneto-optical  Kerr effect infers the existence of in-plane easy magnetization direction. We describe the epitaxial registry condition, the room temperature—zero field magnetic structure observed by magnetic force microscopy and the magneto-optical properties. The observations are consistent with the formation of epitaxial Mn₅Ge₃ alloy, with a modulated magnetic structure characterized by asymmetric 180° Bloch walls consisting of a vortex-like configuration of the local magnetization.     

Influence of ternary addition of transition elements (Cr,Si and Mn) on the microstructure and magnetic properties of nano-structured CuCo alloy

The current state of studies presents the effect of ternary addition of transition elements such as Mn, Cr and Si (10 wt%) on the mechanically driven non-equilibrium solubility of 40 wt% Co containing Cu–Co alloy. X-ray powder diffraction analysis indicates that addition of Mn has been found to be the most effective in enhancing the solubility and formation of a complete solid solution between Co and Cu in a short duration (30 h) of ball milling. The microstructure of the ball milled CuCoMn alloy was found to be stable after the isothermal annealing up to a temperature of 450 °C for 1 h. The magnetic properties such as magnetic saturation, coercivity and remanence of ball milled CuCo alloy in the presence of Mn significantly altered after annealing in the temperature range 350–650 °C for 1 h. The best combination of magnetic properties of CuCoMn alloy has been found after annealing at 550 °C for 1 h.     

Structure and magnetic properties of LaFe11.5−xCoxSi1.5C0.2 compounds for magnetic refrigeration near room temperature

The influence of cobalt on the microstructural, magnetic and magnetocaloric properties of LaFe_11.5−xCo_xSi_1.5C_0.2 (x=0.50–0.85) compounds was investigated. The ingots were prepared by using a vacuum induction melting furnace. Before annealing, a large amount of 1:13 phase was distinctly observed. Nearly single 1:13 phase was obtained after annealing at 1353 K for only 3 days. The easy formation of 1:13 phase in the annealing process could be attributed to carbon doping. The Curie temperature (T_C) increases linearly with increasing the cobalt content. Although the maximum magnetic entropy changes of the compounds decrease rapidly when T_C rises from 275 to 298 K, and it decreases mildly when T_C continues to rise. Two composite refrigerants based on the compounds are proposed. Their entropy changes remains approximately constant over the temperature range from 266 to 292 K and 289 to 309 K.     

Effect of magnetic annealing on magnetostrictive performance of a 〈1 1 0〉 oriented crystal Tb0.3Dy0.7Fe1.95

A 〈1 1 0〉 oriented rod of the alloy Tb_0.3Dy_0.7Fe_1.95 was subjected to a magnetic heat treatment, cooling through its Curie temperature under 240 kA/m. Besides the improved magnetostriction under free conditions, the magnetically annealed rod still exhibited an obvious magnetostriction “jump” effect when subjected to a uniaxial compressive pre-stress. A giant magnetostriction of 2680×10⁻⁶ was achieved under 640 kA/m and 30 MPa, which became 67% larger than before magnetic annealing. The optimum magnetostrictive strain coefficient d₃₃ was also dramatically enhanced. Magnetic force microscopy images show magnetic domain configurations that contribute to the improved magnetostrictive performance. The effect of induced additional anisotropy by magnetic annealing on the improvement of the magnetostriction is also discussed.     

Microstructural and magnetic properties of CoPt nanowires

In this work, the magnetic and microstructural properties of CoPt nanowires are presented as a function of the electrolyte pH and current density during electrodeposition into anodized alumina templates. CoPt nanowires of high aspect ratio have been prepared using electrolyte pH values in the range from 2 to 6. The as-made samples exhibit a face centered cubic (fcc) structure with soft magnetic properties which transform into the face centered tetragonal (fct) L10 phase after thermal treatment. Different pH values of the electrolyte during electrodeposition lead to significantly different microstructures and, therefore, different magnetic properties. The CoPt nanowires prepared at high pH value are composed of fcc nanorods of about 25 nm in length. Thermal annealing of these samples leads to a preferred (0 0 1) orientation (along the direction perpendicular to the direction of nanowires) which increases with annealing time. On the other hand, the CoPt nanowires prepared at lower pH value are composed of uniform fcc nanograins with the size ∼2−3 nm. Magnetization curves for the later sample are virtually identical in both directions indicating an isotropic behavior.     

Optimization of spin-valve parameters for magnetic bead trapping and manipulation

Magneto-optic Kerr effect (MOKE) and magnetoresistance (MR) measurements were used to measure the switching characteristics of spin-valve (SV) arrays currently being developed to trap and release superparamagnetic beads within a fluid medium. The effect of SV size on switching observed by MOKE showed that a 1 μm×8 μm SV element was found to have optimal switching characteristics. MR measurements on a single 1 μm×8 μm SV switched with either an external applied magnetic field or a local magnetic field generated by an integrated write wire (current density ranging from 10⁶ to 10⁷ A/cm²) confirmed the MOKE findings. The 1 μm×8 μm SV low field switching was observed to be +8 and −2 mT with two stable states at zero field; the high field switching was observed to be −18 mT. The low switching fields and the large magnetic moment of the SV trap along with our observation of minimal magnetostatic effects for dense arrays are necessary design characteristics for high-force, “switchable-magnet,” microfluidic bead trap applications.     

The effects of annealing at 1000 °C for 24 h on the extrinsic properties of Pr-Fe-B and Nd-Fe-B-type sintered magnets

Recent studies have shown the effects of a post sintering heat treatment at 1000 °C for 24 h on the microstructure and magnetic properties of Pr-Fe-B/Nd-Fe-B magnets based on Nd₁₆Fe₇₆B₈ and Pr₁₆Fe₇₆B₈. In an attempt to understand the influence of environmental factors, an investigation into the effects of annealing under different degrees of vacuum for both types of sintered magnets has been carried out. The effect of annealing the Pr-Fe-B magnets at 1000 °C for 24 h resulted in a general increase in the magnetic properties, especially the intrinsic coercivity, although the degree of improvement appeared to be dependent on the initial annealing conditions (ambient pressure). Oxygen analysis of sintered and annealed magnets indicates a change in the nature of the grain boundary phases after the annealing treatment. The effect of annealing the Nd-Fe-B magnets at 1000 °C for 24 h resulted in a general decrease in the magnetic properties, especially the intrinsic coercivity.     

Optical sensing characteristics of the photonic crystal fiber filled with magnetic fluid

A novel photonic crystal fiber sensing theory filled with magnetic fluid is proposed based on the change of the MF refractive index under varied magnetic field. The magnetically induced tuning of the magnetic fluid filled PCF propagation properties were investigated by the full-vector finite element method with a perfectly matched layer. Theoretical calculations show that both the effective refractive index and the effective mode area increase vs. the increased magnetic field, and the PCF filled MF with larger d/Λ is more sensitive to magnetic field. When the wavelength λ = 1550 nm, the duty ratio d/Λ = 0.9, d/Λ = 0.6, the effective refractive indexes increase respectively from 1.598279 to 1.617572, from 1.61948 to 1.632484, and the effective mode areas increase respectively from 3.561115 μm² to 7.052360 μm², from 6.167494 μm² to 37.221998 μm² as the magnetic field changes from 25 Oe to 175 Oe. This scheme provides theoretical foundation to use magnetic field to control light in photonic crystal fiber and also offers a potential method for magnetic field sensing based on the TIR-PCF.     

Effects of annealing temperature on structure and magnetic properties of CoAl0.2Fe1.8O4/SiO2 nanocomposites

CoAl_0.2Fe_1.8O₄/SiO₂ nanocomposites were prepared by sol–gel method. The effects of annealing temperature on the structure and magnetic properties of the samples were studied by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and Mössbauer spectroscopy. The results show that the CoAl_0.2Fe_1.8O₄ in the samples exhibits a spinel structure after being annealed. As annealing temperature increases from 800 to 1200 °C, the average grain size of CoAl_0.2Fe_1.8O₄ in the nanocomposites increases from 5 to 41 nm while the lattice constant decreases from 0.8397 to 0.8391 nm, the saturation magnetization increases from 21.96 to 41.53 emu/g. Coercivity reaches a maximum of 1082 Oe for the sample annealed at 1100 °C, and thereafter decreases with further increasing annealing temperature. Mössbauer spectra show that the isomer shift decreases, hyperfine field increases and the samples transfer from mixed state of superparamagnetic and magnetic order to the completely magnetic order with annealing temperature increasing from 800 to 1200 °C.