Magnetic properties of Fe–∼30 at% Pd films

Fe–Pd alloys with about 30 at% of Pd belong to the group of alloys exhibiting a thermoelastic martensitic transformation. The magnetic properties of the Fe–∼30 at% Pd thin films with the disordered FCC structure were examined. A relatively high coercive force of the films was measured. In one of the film samples, a case of out-of-plane magnetization occurred.     

Magnetic properties,microstructure, and phase evolution of PrxFebal.TiyB20−x (x=4–9; y=2.5–5) nanocomposites

Magnetic properties, microstructure, and phase evolution of Pr lean and boron-enriched Pr_xFe_bal.Ti_yB_20−x (x=4–9; y=2.5–5) melt-spinning ribbons with nanostructures have been investigated. Based on thermal magnetic analysis (TMA), for y=2.5, two phases, namely Pr₂Fe₁₄B and α-Fe, were found for ribbons with x=9, while additional two metastable phases, Pr₂Fe₂₃B₃ and Fe₃B, existed for x=4, 7 and 8. With the decrease of Pr content, the remanence increases but coercivity decreases. The optimal properties of B_r=9.5 kG, _iH_c=10.7 kOe, and (BH)_max=17.8 MG Oe are achieved in Pr₉Fe_bal.Ti_2.5B₁₁ nanocomposites. On the other hand, higher Ti substitution for Fe in Pr₇Fe_bal.Ti_yB₁₃ ribbons could refine the grain size and suppress the metastable Pr₂Fe₂₃B₃ and Fe₃B phases effectively. The excellent permanent magnetic properties are mainly dominated by the nanoscaled microstructures and the coexistence of sufficient magnetically soft phases, Fe₃B, Pr₂Fe₂₃B₃ and α-Fe, with magnetically hard Pr₂Fe₁₄B phase.     

Magnetic properties of Fe–Ti–O composite films obtained via solid-phase synthesis

The results from investigating the magnetic and magneto-optical properties of Fe–Ti–O composite films with compositions above the percolation threshold, prepared via a solid-phase reaction with oxygen exchange in layered FeO/Ti structures, are presented. Features of the magneto-optical spectra of prepared films are compared to the spectra of continuous metal films.     

Electrical and switching properties of the Se90Te10−xAgx (0?x?6) films

Amorphous Se₉₀Te_10−xAg_x (0?x?6) films are obtained by thermal evaporation technique under vacuum from the synthesized bulk materials on pyrographite and glass substrates. X-ray analysis shows the amorphous nature of the obtained films. The dc electrical conductivity was studied for different thicknesses (165-711 nm) as a function of temperature in the range (298-323 K) below the corresponding T_g for the studied films. The obtained results show that the conduction activation energy has a single value through the investigated range of temperature which can be explained in accordance with Mott and Davis model. The I-V characteristic curves for the film compositions are found to be typical for a memory switch. The mean value of the threshold voltage increases linearly with increasing film thickness (165-711 nm), while it decreases exponentially with increasing temperature in the investigated range for the studied compositions. The results are explained in accordance with the electrothermal model for the switching process. The effect of Ag on the studied parameters is also investigated.     

Investigation of dielectric properties of newly prepared β-phase polyvinylidene fluoride–barium titanate nanocomposite films

In the present investigation nanocomposite films were prepared by solution casting method with β-phase Polyvinylidene fluoride (PVDF) as a polymer matrix and barium titanate as a filler which was prepared using Ti(IV) triethanolaminato isopropoxide and hydrated barium hydroxide as precursors and tetra methyl ammonium hydroxide (TMAH) as a base. The XRD, FTIR, SEM shows that the fillers in nanocomposites were homogeneous and well dispersed. The dielectric constant and dissipation factors studied in the experimental range of nanocomposites were found to be around 7 and 0.03 respectively which may be very good material to be explored for novel capacitors.     

Correlation between structural and giant magnetoresistance properties of Fe–Ag nanogranular films

Fe _x Ag_1?x granular thin-films, with the atomic Fe concentration, x, ranging from 0 up to 0.5, were deposited by dc magnetron co-sputtering. The giant magnetoresistance (GMR) intensity is maximum at x _I  = 0.32, while the maximum of GMR efficiency, γ, i.e., the change of GMR intensity for a unit change of reduced squared magnetization, is observed at x _γ = 0.26. Owing to the spin-dependent scattering features, the GMR intensity and γ depend on both the concentration and the arrangement of the magnetic material. Therefore, to explain the difference between x _I and x _γ and to understand how the structural properties affect the magnetoresistive behaviour, we performed magnetization, Mössbauer and X-ray diffraction measurements as a function of x. X-ray data indicate that the granular films exhibit three different regimes: for x < 0.2, they can be described as a Fe–Ag solid solution; for 0.2 < x < 0.32 the Fe–Ag solid solution is still observed and very small Fe precipitates are found; finally, for x > 0.32, a Fe–Ag saturated solid solution is detected, containing bcc Fe clusters whose size is about 10 nm. Differently, for all the concentrations, magnetization data show the presence of Fe precipitates, whose size increases with x, and the Mössbauer investigation confirms this picture. We find that the samples grown at x = x _γ display the finest Fe dispersion within the Ag matrix, as the Fe–Ag solid solution is nearly at saturation and the Fe cluster size is of the order of a few nanometers; this arrangement possibly maximizes the magnetic/non-magnetic interface extension thus enhancing the GMR efficiency. If x is slightly increased, the increase in total Fe content compensates the GMR efficiency reduction, so the GMR intensity maximum is observed.     

Anomalous Hall effect in sputter-deposited CoxTi1−xO2–δ films

Hall effect measurements were performed on epitaxial Co_xTi_1−xO_2–δ thin films grown on (0 0 1) LaAlO₃ by reactive RF magnetron co-sputter deposition. Magnetization measurements reveal ferromagnetic behavior in M–H loop at room temperature for Co_xTi_1−xO_2–δ thin films for which x?0.02. An anomalous Hall effect was observed for Co_0.10Ti_0.90O_2−δ films grown with the partial pressure of water P(H₂O)=4×10⁻⁴ Torr or less. These films exhibit a positive ordinary Hall coefficient and a positive magnetoresistance. X-ray diffraction on films grown under these conditions shows evidence for Ti_nO_2n−1 phase due to the deficiency of oxygen. In contrast, Hall measurements taken for undoped and Co-doped TiO₂ thin films grown under more oxidizing conditions show only the ordinary Hall effect with a negative Hall coefficient consistent with n-type conduction. For these films, the magnetoresistance was positive and increased monotonically with increasing magnetic field. The results suggest that Co-doped Ti_nO_2n−1 may be a dilute magnetic semiconducting oxide for which the carriers couple to the spin polarization.     

Magnetic properties of anisotropic Pr–Fe–B films with different deposition rates and pressures

Anisotropic Pr–Fe–B films with hard magnetic properties have been prepared by DC magnetron sputtering on heated Si (100) substrates. The influences of thickness, deposition rate and sputtering gas pressure on the magnetic properties of Pr–Fe–B films were investigated. It is found that the magnetic properties are sensitive to deposition rate and sputtering gas pressure. High deposition rate and argon pressure result in a high coercivity and a low remanence.     

Magnetic properties of low-doped bulk Sr(Ti, Co)O3−δ perovskites

Magnetic properties of bulk SrTi_1−xCo_xO_3−δ solid solutions (for x from 0 to 0.05), prepared in air as those partially reduced, were studied by following the influence of the dopant concentration and valence. A strong paramagnetic and/or diamagnetic contribution and an extremely weak ferromagnetic contribution maintained up to room temperature is observed for all the studied compositions, including the undoped samples. While the paramagnetic contribution shows a classical evolution with cobalt concentration and valence, the ferromagnetic part of the magnetization seems to be independent of the doping process. While some of the observations can support the assumption of an intrinsic property of the SrTiO₃ matrix, the hypothesis of a ferromagnetism associated to some contamination with external magnetic impurities cannot be completely discarded and will be retained here.     

Optical properties of polysiloxane hybrid thin films containing nano-sized Ag–As–Se chalcogenide clusters

Chalcogenide glasses are attractive for all-optical signal processing due to their outstanding optical properties, including large optical nonlinearity, a high refractive index and high photosensitivity. In device fabrication, a challenge lies in the difficulty of obtaining thin films with a high stability and good uniformity. In this paper, optical thin films containing nano-sized chalcogenide clusters in polysiloxane matrices are fabricated by a modified plasma deposition process. The optical absorption and luminescence emission properties of the hybrid thin films were characterized by UV-Vis-NIR and fluorescence spectroscopy. Luminescent emission from Ag–As–Se nano-sized clusters was observed for the first time in these nano-hybrid thin films, and the mechanism was discussed.     

Structure and magneto-optical properties of (CoPt3)1−xNix alloy films

The effect of the Ni addition on the structure and magneto-optical (MO) properties is investigated with (CoPt₃)_1−xNi_x alloy films. The result shows that, lower T_c and higher H_c could be simultaneously obtained in the Ni range of 0.43–0.7. <111>> texture is not the only reason for perpendicular magnetic anisotropy in the present system. Although Ni addition reduces the Kerr rotation angle value in the blue-wave range, it slightly enhances the value in the red-wave range. The films investigated can be considered as suitable for perpendicular magnetic recording applications if the proper Ni addition range (0.43–0.5) is selected. Received: 2 June 1999 / Accepted: 27 October 1999 / Published online: 23 February 2000     

Magnetic properties of (Nd,Pr)–Fe–B nanocomposite over quenched and annealed ribbons

The base alloys of nominal composition (Nd_0.75Pr_0.25)_yFe_balanceB_x (y=10−9.2 and x=6−19.2) were chosen to study the influence of RE/B ratio, smaller than stochiometric composition on magnetic properties of over quenched and annealed ribbons. From X-ray diffraction analysis of these ribbons, the α-Fe and Fe₃B phases were observed along with (Nd,Pr)₂Fe₁₄B major phase. The average grain size was calculated using these patterns as: 35 nm for α-Fe, 45 nm for (Nd,Pr)₂Fe₁₄B and 22 nm for Fe₃B particles. TEM analysis also supported the nano distribution of the above phases. These X-ray graphs support the idea of exchange coupling between hard and soft phases responsible for the observed magnetic properties. In these ribbons the saturation magnetization J_s and remnant magnetization J_r increases from 1.19 T to 1.66 T and from 0.65 T to 0.91 T, respectively as RE/B ratio increases. The increase in J_s and J_r may be attributed to the presence of exchange coupling between these phases. The corresponding coercivity _jH_c decreases from 673.33 to 271.33 k Am⁻¹. The maximum energy product (BH)_max initially increases from 72.42 kJ m⁻³to 109.85 kJ m⁻³ up to RE/B≈1 and then decreases to 58.5 kJ m⁻³, depending on the shape of second quadrant B–H loop. The coercivity mechanism observed from initial hysteresis curve was considered to be nucleation of domain wall.     

High-Jc GdBa2Cu3O7−δ films fabricated by the metal–organic deposition process

We report a successful fabrication of high-J_c GdBa₂Cu₃O_7−δ (GdBCO) films by the metal–organic deposition process on the LaAlO₃ (LAO) (0 0 1) substrates. The coating solution was prepared by mixing Gd, Cu fluorine-free sources with Ba trifluoroacetate. Samples were dip-coated, pyrolized within 3 h at the temperature up to 400 °C in a humid oxygen atmosphere, and finally fired at various high temperatures in 100 ppm Ar/O₂ atmosphere. The GdBCO films fired at 775 and 800 °C exhibited J_c values of ∼2.1 MA/cm² at 77 K in a self-field, which are attributable to both high T_c,zero values of ∼89 K and high in-plane textures of 1.3–1.4°. Above 800 °C, however, the superconducting properties of GdBCO films are degraded due to the thermal decomposition of GdBCO film in 100 ppm Ar/O₂ atmosphere.     

Magnetic properties of Co–Si alloy clusters

We have investigated the electronic structure and the magnetic properties of Co–Si alloy clusters using ab initio spin-polarized density functional calculations. The possible CoSi₂, CoSi, and Co₂Si phase clusters with oblique hexagon prism, icosahedron, and cuboctahedron structures are introduced. The CoSi phase cluster with icosahedron structure has the largest binding energy and amount of charge transfer. We found that HOMO-LUMO gap, magnetic moment, and spin polarization for the Co–Si alloy clusters with icosahedron structure increase with Co concentration. The Si atoms in the CoSi phase with icosahedron structure have negative magnetic moment.     

Magnetic properties of Zn-substituted Li–Cu ferrites

The magnetic properties of Zn-substituted Li–Cu ferrites having the general formula Li_xCu_0.4Zn_0.6−2xFe_2+xO₄ (where, x=0.0, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3) are investigated as a function of Zn content. The X-ray analysis confirms the formation of single-phase of the samples. The lattice parameter increased linearly with Zn content, which is attributed to ionic size differences of the cations involved. The bond lengths R_A and R_B are found to increase with increase in Zn content. The increase of R_A and R_B is attributed to the increase in lattice parameter. The magnetic moment increases with increase in zinc content up to 0.3 and then it decreases with further addition of Zn. The decrease in magnetic moment beyond Zn=0.3 is due to the presence of a triangular spin arrangement on B-site; the three sublattice model suggested by Yafet and Kittle. The initial permeability (μ_i) has been measured, and it is found that it decreases with increase in Zn content. The Curie temperatures also show a decreasing trend.     

High-temperature electronic transport properties of La1−xCaxMnO3+δ (0.0?x?1.0)

La_1−xCa_xMnO_3+δ (0.0?x?1.0) samples were prepared and their resistivity and Seebeck coefficients were measured in the high-temperature range. Ca doping changes the ratio of Mn³⁺/Mn⁴⁺ and influences the electronic transport behavior markedly. With the increase of Ca concentration, the samples change from a p-type semiconductor to an n-type one and Seebeck coefficient becomes increasingly negative. Low doping (x=0.2) and high doping (x=0.8) induces the drop of the resistivity compared with undoped LaMnO_3+δ and CaMnO_3+δ samples due to the rise of carrier concentration. However, the resistivity of moderate-doped samples (x=0.4, 0.6) is larger than low- and high-doped samples because dopant scattering decreases carrier mobility.