Room temperature ferromagnetism of amorphous MgO films prepared by pulsed laser deposition

Amorphous MgO thin films were prepared by pulsed laser deposition (PLD) under various oxygen pressures. The structural, magnetic, and optical properties of the films were investigated. All as-deposited samples exhibit room temperature ferromagnetism, which depend strongly on oxygen pressure. It is found that the saturation magnetization (M _s) initially increases with the oxygen pressure, the maximum M _s of 8.57 emu/cm³ is obtained for the MgO film deposited under an oxygen pressure of 2 mTorr. However, the M _s significantly reduces at higher oxygen pressures. Further X-ray photoelectron spectroscopy and photoluminescence demonstrate that the long-range magnetic order in amorphous MgO films can be attributed to the nonstoichiometry effect and the presence of Mg vacancies.     

Studies of the magnetic and reversal properties for thin CoCrTa films

The effects of magnetic layer thickness on film structural and magnetic properties were studied systematically with emphasis on the thermal effects on thin recording media films. X-ray diffraction measurements reveal structural changes as thickness decreases, and the existence of a “Cr enriched phase” associated with the interface. The saturation magnetization M_s decreases with thickness and the thickness of the “dead layer” was found to be ∼23 Å. Systematic measurements of effective anisotropy, coercivity and saturation magnetization as functions of temperature have been carried out. Magnetic viscosity measurements reveal that thermal stability is affected not only by grain sizes but also by anisotropy reduction associated with nanostructure evolution, as the film thickness decreases.     

The effect of different chemical compositions caused by the variation of deposition potential on properties of Ni-Co films

The magnetic and microstructural properties of Ni-Co films electrodeposited at different cathode potentials were investigated. The compositional analysis revealed that the Ni content increases from 13 at.% to 44 at.% in the films with increasing deposition potential. Magnetic measurements showed that the saturation magnetization, M_s of the films decreased with increase of Ni content as the deposition potential increased. M_s values changed between 1160 emu/cm³ and 841 emu/cm³. The X-ray diffraction revealed that the crystalline structure of the films is a mixture of the predominant face-centered cubic (fcc) and hexagonal closed packed. However, the mixture phase turns to the fcc because of increasing Ni content up to 44 at.% at the highest (−1.9 V) potential by enhancing the intensity of reflections from the fcc phase. The changes observed in the magnetic and microstructural properties were ascribed to the changes observed in the chemical composition caused by the applied different deposition potentials.     

Microwave-induced combustion synthesis of Ni–Zn ferrite powder and its characterization

Ni–Zn ferrite powders were successfully synthesized by microwave-induced combustion process. The process takes only a few minutes to obtain calcined Ni–Zn ferrite powders. The resultant powders were investigated by XRD, SEM, VSM, TG/DTA and surface area measurements. The as-received product shows the formation of cubic ferrite with saturation magnetization (M_s)≈23 emu/g, whereas upon annealing at 850°C for 4 h, the saturation magnetization (M_s) increased to ≈52 emu/g.     

Structural, microstructural and magnetic properties of NiFe2O4, CoFe2O4 and MnFe2O4 nanoferrite thin films

The structural, microstructural and magnetic properties of nanoferrite NiFe₂O₄ (NF), CoFe₂O₄ (CF) and MnFe₂O₄ (MF) thin films have been studied. The coating solution of these ferrite films was prepared by a chemical synthesis route called sol-gel combined metallo-organic decomposition method. The solution was coated on Si substrate by spin coating and annealed at 700 °C for 3 h. X-ray diffraction pattern has been used to analyze the phase structure and lattice parameters. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used to show the nanostructural behavior of these ferrites. The values of average grain's size from SEM are 44, 60 and 74 nm, and from AFM are 46, 61 and 75 nm, respectively, measured for NF, CF and MF ferrites. At room temperature, the values of saturation magnetization, M_s∼50.60, 33.52 and 5.40 emu/cc, and remanent magnetization, M_r∼14.33, 15.50 and 1.10 emu/cc, respectively, are observed for NF, CF and MF. At low temperature measurements of 10 K, the anisotropy of ferromagnetism is observed in these ferrite films. The superparamagnetic/paramagnetic behavior is also confirmed by χ′(T) curves of AC susceptibility by applying DC magnetizing field of 3 Oe. The temperature dependent magnetization measurements show the magnetic phase transition temperature.     

Magnetic and structural properties of nitrified FINEMET powder using mechanical milling method

The magnetic and structural properties of FINEMET [Fe_73.5Si_13.5B₉Nb₃Cu₁ wt%] amorphous powder were investigated after nitrification and mechanical milling. Fe-based amorphous powder were nitrified and crystallized simultaneously at 550 °C using by ammonia (NH₃) gas. Nitrified powder exhibited iron nitride phase such as γ′-Fe₄N, Fe₃N, and α″-Fe₁₆N₂. Nitrified particles were more brittle than raw particles. As a result, nanometer-sized nitride powder was fabricated by high-energy ball milling method. The saturation magnetization (M_s) and coercivity (H_c) of nitrified powder were increased due to nitride phase.     

Magnetization reversal in Fe48Pt34B34 magnetic foils

Exchange-spring magnet L1-FePt/(Fe₂B+α-Fe) is fabricated by flash annealing a melt-spun Fe₄₈Pt₃₄B₃₄ foil. A coercivity of 8500 Oe (1 Oe = 79.5775 A/m), squareness (M_r/M_s) of 0.70, saturation magnetization of 10.2 kGs (1 Gs = 10^-4 T) and an effective anisotropy K_eff =2.0 × 10⁷ ergs/cm³ are obtained. A two-step magnetization reversal feature is characterized in this paper. An exchange bias phenomenon is also observed in a low saturation field.     

Magnetic characterization of surface-hardened steel

Case depth measurements of surface-hardened steel parts are important for quality control. Here, the magnetic properties of two sets of carefully characterized 25-mm-diameter case-hardened steel rods were studied with the aim of developing new methods to evaluate the case depth nondestructively. Induction-hardened 4140 steel and carburized 8620 steel rods were studied. Each set contained control samples (heat-treated but not surface-hardened) and samples hardened to three different nominal depths. After fabrication, the microhardness profiles of the rods were measured and the data analyzed to obtain the mid-hardness depth in each case. These measurements were compared with optical micrographs that reveal the microstructure of the samples as a function of depth below the surface.By the analysis of measured magnetization curves and hysteresis loops, the differential permeability and saturation magnetization of the rods were extracted. It was found that differential permeability increases with increasing case depth at a certain strength of the applied field (1350-1450 A/m) for both hardening mechanisms, but only significantly for induction-hardened rods. Saturation magnetization M_s was evaluated using the ‘law of approach’ and was observed to decrease as the depth of case hardening increases, for both induction-hardened and carburized steel rods. The observed behavior is described adequately by a simple model in which M_s for the rod is represented as a volume-weighted sum of saturation magnetization values in the core and in the surface layer.     

Magnetic properties and domain structures of FeSiB thin films

Smooth Fe₇₈Si₁₀B₁₂ thin films were prepared by r.f. sputtering with the very slow deposition rate of 0.59 nm/min. The as-deposited films were not fully amorphous, instead α-Fe(Si) nanocrystallites were found to be embedded in the amorphous matrix. The saturation magnetostriction λ_s of the as-deposited film is about 6.5 × 10⁻⁶. After annealing at 540 °C for 1 h in an ultrahigh vacuum (4.5 × 10⁻⁵ Pa), the fraction of α-Fe(Si) crystalline phase largely increased, and correspondingly the λ_s decreased to 4.5 × 10⁻⁷. Ripple domain structures were observed in the as-deposited film, while dense stripe domains were observed in the annealed sample, characterized by a very narrow domain width of 80 nm. (1 1 0) texture and island-like configuration of α-Fe(Si) nanocrystallites formed by the annealing treatment are responsible for the perpendicular anisotropy. For the as-deposited film, the magnetization curves increased linearly with the increase of the magnetic field, and showed the very small hysteresis. On the other hand, the annealed sample clearly showed a very steep jump near the origin, which is due to the switch process of the dense stripe domain.     

Correlator of the quark scalar currents and Γtot(H → hadrons) at O(αs) in pQCD

We present the results of the analytical evaluation of the massless four-loop

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(α³_s) correction to the correlator of the quark scalar currents and the Higgs decay rate into hadrons. In numerical form we found (in

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scheme) that Γ (H →

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b ) = (3G_F/4

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π) M_Hm²_b (M_H) [1 + 5.667α_s/π + (35.94 − 1.359n_f) (α_s/π)² + (164.139 − 25.771n_f + 0.259n²_f) (α_s/π)³] where n_f is the number of quark flavour and α_s = α_s(M_H).     

Magnetic properties of thin epitaxial Gd films on Nb

We investigated the magnetic properties of Gd films by magnetization measurements with the transverse magnetooptic Kerr effect in the temperature range from 2 to 295 K and for magnetic field up to 0.3 T. The thicknessd _Gd of the Gd films was varied between 11 and 1000 Å. For thick films (d _Gd500 Å) the form of the hysteresis curves and especially the nonmonotonic temperature dependence of remanence and coercivity can be qualitatively reproduced with a simple model employing theT dependence of the easy-axis direction. TheT dependence of the saturation magnetizationM _s of the thick films (d _Gd>=150 Å) strongly resembles the behavior of bulk crystals, whereas for the thinnest filmsM _s approximately depends linearly onT up to the Curie temperatureT _C . The thickness dependence ofT _C follows approximately a power law with an exponent 1.6 close to the theoretical value.     

Anomalous magnetization processes and non-symmetrical domain wall displacements in L10 FePt particulate films

Anomalous magnetization processes and non-symmetrical domain wall displacements in the minor loop of L1₀ FePt particulate films were investigated by magnetization measurements and in situ magnetic force microscopy. Magnetization (M) decreases dramatically on increasing the magnetic field to ∼3 kOe after which M becomes small and constant in the range of 5–20 kOe as observed in the successive measurement of minor loops. The domain wall displacement is non-symmetrical with respect to the field direction. The anomalous magnetization behavior was attributed to the non-symmetrical domain wall displacement and large magnetic field required for domain wall nucleation. Energy calculations from modeling suggest that non-symmetrical domain wall displacement is caused by the existence of metastable domains in which the domain edges are stuck to the particle boundaries.     

Preparation of magnetic FeCo nanoparticles by coprecipitation route

Magnetic FeCo nanoparticles with high saturation magnetization (M_s = 148 emu/g) at 15 kOe were prepared by a coprecipitation route. The value of M_s for FeCo nanoparticles depends on the ratio of Fe to Co components. The size of the nanoparticles was confirmed by transmission electron microscopy (TEM) images, and morphology of the nanoparticles was obtained by field emission scanning electron microscopy (FE-SEM) images. The crystal structure of the nanoparticles dependent on annealing was characterized by X-ray diffraction data. The magnetic properties were characterized by saturation magnetization from a hysteresis loop by VSM.     

Magnetic properties of single crystalline Zn1−xCoxO thin films

We report on the magnetic properties of single crystalline thin films of Zn_1−xCo_xO (x=0.003–0.14) grown by plasma-assisted molecular beam epitaxy. In order to understand the role of intermediate charge carriers in the magnetic properties of this material two types of films were fabricated, with and without Ga-codoping. Magnetic measurements were made between 2 and 300 K in fields up to 5 T with a Quantum Design SQUID magnetometer. We found that all the tested films exhibit paramagnetic behavior following the Curie–Weiss law, χ=C/(T−θ), with negative Curie–Weiss temperatures and that this behavior holds even under strong n-doping. We show that the magnetization data, M(H), in function of the Co content provide additional evidence in favor of the antiferromagnetic Co–Co interaction in this material. We also observe that these data exhibit an ‘easy plane’ magnetic anisotropy for all the studied Co concentrations. Finally, we develop a simple cluster model, in order to describe the magnetic properties of ZnCoO, which is found to be in good agreement with our experiments.     

Magnetic properties of CoFeP films prepared by electroless deposition

Structure and magnetization of CoFeP films prepared by the electroless deposition were systematically investigated by varying the bath composition and deposition parameters to optimize soft magnetic properties. The cobalt content in the CoFeP films varies from 40.4 to 94.9 wt% by controlling the bath composition. Increase of the metallic ratio FeSO₄·7H₂O/(CoSO₄·7H₂O+FeSO₄·7H₂O) affects the films’ microstructure, which switches from amorphous to crystalline structure. The magnetic properties of CoFeP films reveal that the coercivity (H_c) values range from 80 up to 185 A/m and the saturation magnetization (M_s) from 82 to 580 eum/g depending on the bath composition, deposition parameters and heat-treatment conditions. Increase of M_s and remanent magnetization (M_r) as well as decrease of H_c are observed for the CoFeP films with bath pH, temperature and the metallic molar ratio increasing. It is also found that the H_c is enhanced with the increase of NaH₂PO₂·H₂O concentration. CoFeP films showing good soft magnetic properties with coercivities less than 140 A/m and M_s close to 600 emu/g can be obtained in high pH bath and thereafter heat treatment. The deposit is found to be suitable as soft magnetic materials for core materials.     

Effects of high-temperature annealing on magnetic ordering in thin films of Bi2O3-CaO-Fe2O3

Magnetic properties of rf sputtered (0.5–x) Bi₂O₃-x CaO-0.5 Fe₂O₃ (x=0–0.5) have been studied through magnetization and ferromagnetic resonance (FMR) measurements. Films prepared in a mixed oxygen-argon atmosphere are amorphous and paramagnetic. Samples annealed in air at temperatures of 700–1000 K show a ferrimagnetic behavior even though X-ray diffraction data for the films do not indicate the precipitation of any crystalline ferrimagnetic compounds. The room-temperature saturation magnetization 4M and the uniaxial anisotropy field H _u , decrease with increasing x. The Curie temperature and the gyromagnetic ratio increase with increase in the concentration of CaO. Studies on the effects of sputtering atmospheres on magnetic parameters show that films sputtered in oxygen-rich atmospheres have a large 4M and H _u , and a relatively small and FMR line-width. Ordered amorphous clusters are suggested to give rise to the observed ferrimagnetic character in the annealed films.     

复合薄膜NiFe2 O4-BiFeO3 中的磁电耦合

采用化学溶液沉积法(CSD)在Au/Ti/SiO₂/Si衬底上通过自组装生长制备了BiFeO₃-NiFe₂O₄ (BFO-NFO)多铁性复合薄膜.X射线衍射图谱(XRD)显示形成了分离的钙钛矿结构的铁电相BFO和尖晶石结构的铁磁相NFO. NFO的引入导致复合薄膜的泄漏电流减小,剩余极化强度增加.相比于纯BFO薄膜,0.25NFO-0.75BFO样品泄漏电流下降了约两个数量级,剩余极化强度( M _{关键词： 多铁性复合薄膜 磁电耦合 铁电性 铁磁性}     

Magnetic properties of a Pt/Co2FeAl/MgO structure with perpendicular magnetic anisotropy

Microstructures and magnetic properties of Ta/Pt/Co 2 FeAl（CFA）/MgO multilayers are studied to understand perpendicular magnetic anisotropy（PMA） of half-metallic full-Heusler alloy films.PMA is realized in a 2.5-nm CFA film with B2-ordered structure observed by a high resolution transmission electron microscope.It is demonstrated that a high quality interface between the ferromagnetic layer and oxide layer is not essential for PMA.The conversions between in-plane anisotropy and PMA are investigated to study the dependence of magnetic moment on temperature.At the intersection points,the decreasing slope of the saturation magnetization（M s） changes because of the conversions.The dependence of M s on the annealing temperature and MgO thickness is also studied.     

On the profile of temperature dependent electrical and dielectric properties of Au/SiO2/n-GaAs (MOS) structures at various frequencies

The temperature (T) dependence of electrical and dielectric characteristics such as series resistance (R_s), dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tan δ), and real and imaginary part of electrical modulus (M′ and M″) of the Au/SiO2/n-GaAs (MOS) structures have been investigated in the temperature range of 80–350 K at various frequencies by using experimental capacitance (C) and conductance (G/w) measurements. Experimental results show that both C and G/w characteristics were quite sensitive to frequency and temperature at especially high temperatures and low frequencies due to a continuous density distribution of interface states and their relaxation time, and thermal restructuring and reordering of the interface. Series resistance values of this device obtained from Nicollian method decrease with increasing frequency and temperature. The ε′, ε″, tan δ, and M′ and M″ were found a strong function of frequency and temperature. While the values of ε′, ε″, and tan δ decrease, M′ and M″ increase with increasing frequency. Also, while ε′ and ε″ increase, M′ and M″ decrease with increasing temperature. The tan δ and M′ values are almost independent temperature especially at high frequencies (f≥500 kHz).     

面内场和静态偏磁场作用下条畴和泡畴的稳定性

实验研究面内场H_in和静态偏磁场H_b作用下,(111)面磁泡膜内条畴的消失过程。保持H_b恒定,增加H_in,测量条畴消失场H_s^*和泡畴消失场H_k^*与面内场方向β的变化关系。计及立方磁晶各向异性的影响,建立H_in和H_b共同存在时的条畴稳定性理论。定性解释了实验的主要特点。导出黑、白条畴同时消失时的角度 β_n=1/3(2nπ±arc cos│3/(2^1/2)(M_sH_b)/K₁│)(n=0,±1,±2,…)与实验基本符合。 关键词：