XANES investigations of interatomic interactions in multilayered nanostructures (Co45Fe45Zr10/a-Si)40 and (Co45Fe45Zr10/SiO2)32

The electronic structure and phase composition of amorphous multilayered nanostructures (Co₄₅Fe₄₅Zr₁₀/a-Si)₄₀ and (Co₄₅Fe₄₅Zr₁₀/SiO₂)₃₂ have been investigated by means of the X-ray absorption near-edge structure (XANES) technique, which is the most sensitive and useful in investigation of the chemical environment of elements in multicomponent nanostructures. The fact of interatomic interactions leading to the formation of composite “nanoferrite”-like FeO · Fe₂O₃ · ZrO₂(CoO) was established. Also it was shown that in the mentioned nanoferrite there is an exchange interaction which involves not only two- and three-charged ions of iron (Fe²⁺ and Fe³⁺) but also ions like Zr⁴⁺ and, partially, Co²⁺. The transformation of the thin structure of L _2,3-ranges for the iron component of multilayered nanostructures in XANES spectra reflects on the change of the ratio of di- and trivalent ions in iron oxides as a part of the composite “nanoferrite.”     

X-Ray photoelectron spectroscopy investigations of atomic interactions in surface layers of multilayered nanostructures (Co45Fe45Zr10/a-Si)40 and (Co45Fe45Zr10/SiO2)32

The interatomic interaction and chemical state of elements in amorphous multilayered (Co₄₅Fe₄₅Zr₁₀/a-Si)₄₀ and (Co₄₅Fe₄₅Zr₁₀/SiO₂)₃₂ nanostructures with different interlayers have been investigated by X-ray photoelectron spectroscopy using synchrotron radiation. The results of X-ray photoelectron spectroscopy investigations have demonstrated that, in surface layers of all the studied multilayered structures, the metallic layer components Co, Fe, and Zr are in the oxidized state. The silicon state is found to be identical and close to the state of nonstoichiometric silicon oxide, regardless of the presumed compositions of SiO₂ and a-Si interlayers. After the removal of surface layers of the multilayered structures in the sample preparation chamber by ion etching, the metallic layer components Co, Fe, and Zr are predominantly in the elemental state.     

Planar Hall effect and anisotropic magnetoresistance in layered structures Co0.45Fe0.45Zr0.1/a-Si with percolation conduction

Magnetic and magnetotransport properties of multilayered nanostructures Co_0.45Fe_0.45Zr_0.1/a-Si obtained by ion-beam sputtering are investigated. The temperature dependence of the resistance obeys a law of the form R _xx ∝-logT, which is typical of metal-insulator nanocomposites on the metal side of the percolation transition. The magnetoresistance anisotropy effect, as well as the planar Hall effect, is observed for the first time for this type of nanocomposites in the vicinity of the percolation transition. The correlation of these two effects with the transverse (between Hall probes) magnetoresistive effect, which may reach 6–9%, is revealed. A weak negative magnetoresistance of the order of 0.15%, which is observed for subnanometer amorphous silicon layer thicknesses, is attributed to spin-dependent electron transitions between adjacent ferromagnetic layers in the case when the exchange interaction between these layers is of the antiferromagnetic type.     

Preparation and characterization of the ZnO:Al/Fe65Co35/ZnO:Al multifunctional films

The ferromagnetic transparent conducting film is a multifunctional film which has high visible transmittance, low resistivity and room-temperature ferromagnetism, simultaneously. In this article, ferromagnetic transparent conducting ZnO:Al/Fe₆₅Co₃₅/ZnO:Al multilayer films were fabricated by inserting a middle magnetic Fe₆₅Co₃₅ layer into aluminum-doped zinc oxide (ZnO:Al) matrix using a magnetron sputtering apparatus at substrate temperature ranging from room temperature (RT) to 400^∘C. The total film thickness was about 400 nm and the middle Fe₆₅Co₃₅ alloy layer was 4 nm. The influences of substrate temperature (T _s ) on the structural, electrical, optical and magnetic properties of the multilayer films were systemically investigated. The results showed that the microstructure and performance of the composite multilayer films strongly depended on the substrate temperature. The present results also showed that the inserted middle Fe₆₅Co₃₅ alloy thin layer played an important role in providing the RT ferromagnetism and decreasing the resistivity of the multilayer films. Therefore, it is possible to obtain a multifunctional film material with the combination of good optical transparency, high electrical conductivity and RT ferromagnetism.     

Thickness-dependent magnetic properties of Ni81Fe19, Co90Fe10 and Ni65Fe15Co20 thin films

We present results of magnetization and magnetic anisotropy measurements in thin magnetic films of the alloys Ni₈₁Fe₁₉, Co₉₀Fe₁₀ and Ni₆₅Fe₁₅Co₂₀ that are commonly used in magnetoelectronic devices. The films were sandwiched between layers of Ta. At room temperature the critical thickness for all the films to become ferromagnetic is in the range 11–13 Å. In Co₉₀Fe₁₀ the coercivity and the anisotropy field both depend strongly on layer thickness.     

The piezoelectric effect in Pb[(Fe1/3Sb2/3) x Ti y Zr z ]O3 ceramics

The piezoelectric properties of Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃ with x + y + z = 1, x = 0.1, y = 0.43–0.48 ceramics have been investigated over a broad temperature range using a resonance technique. The influence of modification of PZT normal ferroelectric synthesized near the morphotropic phase boundary by a relaxor Pb(Fe_1/3Sb_2/3)O₃ compound on its physical properties was studied. The coefficients s ₁₁, k ₃₁, and d ₃₁ were calculated from the parameters characterizing the behavior of damped harmonic oscillator in the vicinity of the piezoelectric resonance. Several anomalies of the piezoelectric coefficients have been found in the temperature range 300–600 K. Two diffuse phase transitions were observed in Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃. The anomaly near 530 K for y = 0.43 is responsible for the transition from the rhombohedral phase to the tetragonal one. For y > 0.44 this transition is found to be very diffuse and the coexistence of rhombohedral and tetragonal phases occurs. The observation of low piezoelectric activity confirms the existence of polar regions in Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃ above T _m.     

Electrical transport in ferroelectric Pb[(Fe1/3Sb2/3) x Ti y Zr z ]O3 ceramics

In this article, the studies of the polarization currents and current–voltage characteristics (J–V) are presented. The measurements of the J–V in low and high temperatures as well as at low and high voltages have permitted to recognize certain details of local energy levels in forbidden gap. It has been possible to calculate energy trap levels and their concentration. Calculated trap energy and concentration, under the condition of single trap energy levels, are equal: E _t = 0.55 eV, N _t = 2.97 · 10²³ m^?3 for the sample y = 0.44 and E _t = 0.59 eV, N _t = 1.5 · 10²³ m^?3 for the sample y = 0.47. Knowing the J–V characteristic and the Seebeck coefficient the carriers concentration and their mobility can also be calculated. The carriers concentration and their mobility are equal: n = 3.8 · 10¹⁸ m^?3, µ = 1.4 · 10^?12 m² V^?1 · s^?1 for sample y = 0.44 and n = 6.9 · 10¹⁶ m^?3, µ = 1.3·10^?11 m² V^?1 · s^?1 for the sample y = 0.47.     

Structural,magnetic, and electrical properties of thin film Pd/Co layered structures

We report on properties of layered coherent structures of Pd and Co, prepared by RF sputtering. X-ray diffraction analysis characterizes these films as having a well-ordered periodic structure (periods λ in the range 10A < λ < 80A) of stacked (111) planes of fcc Co and Pd. Room temperature magnetic properties were measured with a vibrating sample magnetometer. All films are ferromagnetic, with a magnetic moment in excess of that attributable to Co. This excess, which increases as λ decreases, is interpreted as induced ferromagnetism in the Pd layers. The in-plane magnetization is harder for smaller values of λ and appears to depend mainly on the thickness of the Co layers. The in-plane electrical resistivity was measured in the range 2K–300K by a four-electrode method. Below 40K, the resistivity is dominated by residual resistivity; above this temperature, its rise is attributed mainly to the resistivities of bulk Pd and Co. The λ-dependence of the resistivity is described by a model of interfacial scattering of electrons. Evidence for the presence of coherency strains at small λ is present in the x-ray data, the magnetization behavior, as well as in the interfacial scattering mechanism deduced from the analysis of the resistivity.     

Structure and magnetic properties of magnetron-sputtered [(Fe/Pt/Fe)/Au]n multilayer films

Using dc magnetron sputtering, Fe/Pt/Au multilayer films were prepared, and the effects of Au layer thickness and annealing temperature on structure and magnetic properties of the Fe/Pt/Au multilayer films were investigated. The as-deposited Fe/Pt/Au multilayer films have good periodic structure with composition modulation along the growth direction. The stress stored in the as-deposited films promoted the ordering of the films annealed at 400 °C. When the films were annealed at 500 °C, the thicker Au layer could restrain the order-disorder transformation region volume and lead to the decrease of the ordered volume fraction with Au layer thickness increasing.     

2,3-二羟基萘钼多酸有机衍生物的合成及1H NMR和IR谱学研究

本文对二种新合成的2，3－二羟基萘二钼和四钼多酸有机衍生物[n-Bu)4N]2[Mo2O5(OC10H6O)2](Ⅰ）和[n-Bu)4N]2[Mo4O10(OC10H6O)2(OCH3)2](Ⅱ)进行了红外光谱与核磁共振波谱研究，发现[Mo2O5]^2 中钼氧多桥键的红外振动频率较[Mo4O10(OCH3)2]^2 中钼氧多桥键的红外振动频率红移，而在配合物Ⅱ中2，3－二羟基中芳环的^1H化学位移较配合物Ⅰ中向低场移动。同时还发现含二钼配位中心[Mo2O5]^2 的[Mo2O5(OC10H6O)2]^2-与含四钼配位中心[Mo4O10(OCH3)2]^2 的[Mo4O10(OC10H6O)2(OCH3)2]^2-生成条件的差异仅仅只在反应体系的pH值的微小变化，说明钼多酸有机衍生物阴离子是对体系酸碱度极为敏感的物质。     

Microfabrication and magnetoelectric properties of amorphous magnetic-tunnel-junctions with Co–Fe–B/Al–O/Co–Fe–B hardcore structure

Both single-barrier magnetic tunnel junctions (SBMTJs) and double-barrier magnetic tunnel junctions (DBMTJs) with an amorphous hardcore structure of Co₆₀Fe₂₀B₂₀/Al–O/Co₆₀Fe₂₀B₂₀ were microfabricated. A high TMR ratio of 102.2% at 4.2 K was observed in the SBMTJs after annealing at 265 °C for 1 h. High TMR ratio of 56.2%, low junction resistance-area product RS of 4.6 kΩ μm², small coercivity H_C=25 Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V_1/2 greater than 500 mV at room temperature (RT) had been achieved in such Co–Fe–B SBMTJs. Whereas, high TMR ratio of 60% at RT and 89% at 30 K, low junction resistance-area product RS of 7.8 kΩ μm² at RT and 8.3 kΩ μm² at 30 K, low coercivity H_C=8.5 Oe at RT and H_C=14 Oe at 30 K, and relatively large bias-voltage-at-half-maximum TMR with the value V_1/2 greater than 1150 mV at RT had been achieved in the Co–Fe–B DBMTJs. Temperature dependence of the TMR ratio, resistance, and coercivity from 4.2 K to RT, and applied voltage dependence of the TMR ratio and resistance at RT for such amorphous MTJs were also investigated.     

Thermal stability,magnetic and magnetocaloric properties of Gd55Co35M10 (M = Si,Zr and Nb) melt-spun ribbons

The thermal stability, magnetic and magnetocaloric properties of Gd₅₅Co₃₅M₁₀ (M = Si, Zr and Nb) melts-pun ribbons were studied. The relatively high reduced glass transition temperature (T_x1/T_m > 0.60) and low melting point (T_m) resulted in excellent glass forming ability (GFA). The Curie temperatures (T_C) of melt-spun amorphous ribbons Gd₅₅Co₃₅M₁₀ for M = Si, Zr and Nb were 166, 148 and 173 K, respectively. For a magnetic field change of 2 T, the values of maximum magnetic entropy change (−ΔS_M)^max for Gd₅₅Co₃₅Si₁₀, Gd₅₅Co₃₅Zr₁₀ and Gd₅₅Co₃₅Nb₁₀ were found to be 2.86, 4.28 and 4.05 J kg⁻¹K⁻¹, while the refrigeration capacity (RC) values were 154, 274 and 174 J kg^–1, respectively. The RC_FWHM values of amorphous alloys Gd₅₅Co₃₅M₁₀ (M = Si, Zr and Nb) are comparable to or larger than that of LaFe_11.6Si_1.4 crystalline alloy. Large values of (−ΔS_M)^max and RC along with good thermal stability make Gd₅₅Co₃₅M₁₀ (M = Si, Zr and Nb) amorphous alloys be potential materials for magnetic cooling operating in a wide temperature range from 150 to 175 K, e.g., as part of a gas liquefaction process.     

Surface vs. bulk magnetic properties of Co/Fe(0 0 1) and Fe/Co/Fe(0 0 1) as probed by linear magnetic dichroism in photoemission

The atomic-like behavior of the photoionization cross-section of core levels in solids is remarkably displayed in the observation of linear magnetic dichroism in the angular distribution (LMDAD) of photoelectrons. Nevertheless, structure-related effects are clearly visible as modulations of the dichroism signal, induced by photoelectron diffraction (PED). In this paper a comparison between the PED and LMDAD behaviours is presented for Fe 3p in Fe(0 0 1). In order to separate experimentally the surface and bulk contributions, ultrathin Co/Fe pseudomorphic overlayers were grown on the Fe(0 0 1) surface. Results confirms the PED nature of LMDAD modulations, which can be used as an estimate of the bulk sensitivity of the experiment.     

Effect of cooling rate in [(Fe0.5Co0.5)0.75B0.2Si0.05]100-xNbx alloy system on magnetic properties

The effect of cooling rate on the thermal stability and soft magnetic properties of [(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]_100-xNb_x (x = 5, 6, 7, 8 at. %) system was investigated. The alloys were produced into the form of ribbon and cylindrical rod by melt-spinning and injection casting, respectively. Their structure, thermal, mechanical and soft magnetic properties were investigated by x-ray diffraction, differential scanning calorimetry, universal testing machine and vibrating sample magnetometer, respectively. All of the alloys were identified as fully amorphous by X-ray diffraction. It turned out that the rod samples had exceptionally high saturation fields reaching 3.0 kOe, which is key properties for sensor application. Also, among these Fe,Co-based samples, the Fe_35.25 Co_35.25 B_18.8 Si_4.70 Nb₆ ribbon exhibits the highest saturation magnetization with 142.1 emu/g.     

Growth,electronic properties and thermal stability of the Fe/Al2O3 interface

Soft X-ray photoelectron spectroscopy and resonant photoemission have been used to study the growth and electronic properties of Fe ultrathin films deposited on Al₂O₃ substrates. A simultaneous multilayer growth mode has been found for Fe growth at room temperature. For iron coverages below 1 ML, Fe²⁺ species are formed at the Fe/Al₂O₃ interface, followed by the formation of a metallic iron overlayer. The bonding of Fe at very low coverages occurs by charge transfer from Fe to surface oxygen atoms, and neither hybridisation of Fe and Al states nor reduction of the Al₂O₃ substrate are observed. The thermal stability of the interface has been also studied in the range 673–873 K. Annealing produces Fe agglomeration in such a way that some areas of the Al₂O₃ substrate become fully Fe-depleted. In these Fe-depleted areas, Fe²⁺ completely disappears and Al⁰ reduced species are formed. This behaviour would explain the decrease in the magnetoresistance performance of magnetic tunnel junctions after annealing above 573 K.     

Study of the [(Co45Fe45Zr10)x(Al2O3)100−x/a-Si:H]m multilayer nanostructure by polarized neutron reflectometry

Polarized neutron reflectometry was used to investigate the amorphous multilayer nanostructures [(Co₄₅Fe₄₅Zr₁₀)_x(Al₂O₃)_100−x/a-Si:H]_m, whose magnetic properties are dependent on the concentration of the magnetic constituent (x=34, 47 and 60 at%) as well as on the thicknesses of the metal-dielectric (Co₄₅Fe₄₅Zr₁₀)_x(Al₂O₃)_100−x and semiconductor a-Si:H layers. The average magnetization of the individual magnetic layer is found to be inhomogeneous with the magnetically active central part and two magnetically dead parts at the interfaces.     

Microstructure and magnetic properties of multilayered [Fe/Pt]n structures prepared by successive deposition

The structure and magnetic properties of multilayered [Fe/Pt]n structures prepared by successive magnetron sputtering of Fe and Pt plates and deposition of Fe and Pt layers on a preliminarily heated glass substrate have been studied as functions of the number n and thickness of the layers. Mössbauer studies and measurements of magnetic hysteresis loops (MH) have established that [Fe/Pt]n films for n = 16 exhibit primarily magnetic anisotropy normal to the film plane. Data obtained by X-ray photoelectron spectroscopy (XPS) strongly suggest that the films have an interface between the substrate and the multilayered structure. Our micromagnetic modeling leads to the conclusion that the magnetic anisotropy oriented normal to the [Fe/Pt]n film plane (for n = 16) is induced by formation of an anisotropic interface.     

The effect of the sputtering process ambient on the magnetic state and phase composition of the film nanocomposites (Fe0.45Co0.45Zr0.10) x (Al2O3)1−x

The effect of oxygen-containing ambient arising at sputtering of granular nanocomposites (Fe_0.45Co_0.45Zr_0.10) _x (Al₂O₃)_1−x (30 at.%≤x≤65 at.%) on their magnetic state and phase composition has been investigated. It was shown that the presence of oxygen resulted in the formation of oxide shells preventing the ferromagnetic interaction between Co_0.45Fe_0.45Zr_0.10 nanoparticles and also the formation of metallic percolative net beyond the percolation threshold (as opposed to the films prepared in pure argon atmosphere).