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Bilayer is an effective structure to enhance magnetic properties of films. This study employs high magnetic field (HMF) and amorphous Fe–Sm under-layer to tune the magnetic properties of evaporated Co–Sm/Fe–Sm bilayer films. Various analysis methods are used to explore the relation of microstructure evolution under above conditions with magnetic performance. The results show that both the amorphous Fe–Sm under-layer and the HMF can decrease surface roughness. Further, the HMF exhibits other effects that reduces column size, increases interplanar spacing and affects interface at atomic scale. The structural variation has effect on magnetic properties of bilayer films. The amorphous Fe–Sm under-layer increases magnetization, coercivity and squareness through changing the amount of non-magnetic structure at atomic scale. Meanwhile, the HMF decreases coercivity by changing pinning via the interface variation. Both the HMF and amorphous under-layer have no influence on the anisotropy of bilayer films. These results present an effective method to tune the magnetic properties of films through amorphous under-layer and HMF. • Amorphous FeSm under-layer has effect on microstructure and magnetic performance. • High magnetic field improves magnetization by affecting non-magnetic structure. • High magnetic field decreases coercivity by changing interface pinning. • Effect of high magnetic field on squareness is smaller than that of amorphous layer. [ABSTRACT FROM AUTHOR]

• Annealing and high magnetic fields (HMFs) adjusted growth structure of Fe films. • Different-stage HMFs and annealing suppressed strain and roughness of Fe films. • 10% larger M s than Fe bulk was obtained by combined film-growth HMF and annealing. • HMF and annealing decreased coercivity but increased remanence ratio of Fe films. • Film-growth HMF and annealing effectively adjust structure and improve properties. To improve the magnetic properties of films applied in spintronic devices, this article explored the microstructure and magnetic properties of Fe nanocrystalline films via annealing and applying high magnetic field (HMF) during different film-formation stages. The results indicate that both annealing and HMF inhibited the sloping and overlapping of the columnar grains in the as-deposited film. Annealing promoted the formation of nanoparticles, while annealing with HMF arrayed the columnar grains along the direction of HMF. A chain arrangement with mixture columnar grains and nanoparticles was observed by combined film-growth HMF and annealing. Different-stage HMFs and annealing improved the particle size but suppressed the stain and surface roughness of the Fe films. The film-growth HMF and annealing both enhanced the saturation magnetization (M s) of the Fe films. Especially, combined film-growth HMF and annealing obtained 10% larger M s than Fe bulk. The low disordered structure, average grain size and grain shape anisotropy under film-growth HMF and annealing remarkably decreased the coercivity (by 91%) but increased the remanence ratio (by 67%) of films. However, annealing with HMF did not obviously improve the magnetic properties of Fe films. These indicated that film-growth HMF and annealing provide useful ways to adjust structure and enhance properties. [ABSTRACT FROM AUTHOR]

Position of impurities at point defects of a compound have an important role in determine the physical or chemical properties of semiconductor materials. Hence, an accurate and efficient theoretical tool is needed in order to have a deep understanding and logic explanation for the physical phenomenon observed. Therefore, first principles calculation was used to investigate the effect of impurities position at point defects of Au atom in the ZnO semiconductor material on thermoelectric and magnetic performance. In this work, density functional theory based on the generalized-gradient-approximation (GGA) and the Boltzmann transport theory have been used to calculate the structural, electronic, magnetic and thermoelectric properties of Au doped ZnO at different point defect's position (interstitial and substitutional). The obtained results give a hexagonal wurtzite structure with the space group of P 63 mc and the formation energy at the interstitial model indicated 0.2331 eV lower rather than the substitution model. This indicated more stable structure at the interstitial sites with n -type degenerated semiconductor characteristic and behaves as a diamagnetic material with highest electronic thermal conductivity. Whereas, the substitution of Zn by Au produces p -type semiconductor characteristics with the presence of magnetism properties (0.916 μ b of total magnetic moment) and enhance the electrical conductivity properties. The Seebeck coefficient obtained is in excellent accord with the experimental data of Au doped ZnO. The result shows that Au doped ZnO can be used in the thermoelectric power generated in magnetic tunnel junction (MTJ) applications. • Magnetic and thermoelectric properties of Au doped ZnO at different point defects are investigated with DFT. • Substitution model show that Au doped ZnO is ferromagnetic, interstitial show paramagnetic behavior. • Hybridization between p-d states are responsible for electrical transport properties and magnetic properties. [ABSTRACT FROM AUTHOR]

Control and improvement of the magnetic and electrical properties of magnetic nanocrystalline films are very essential for their applications in spintronics and magnetic storages. This paper studies the effects of high magnetic field (HMF) on the microstructure, soft magnetic and electrical transport properties of the Co nanocrystalline films. It was found that the Co films without HMF were disordered stack of spherical nanoparticles. The stack changed to columnar structure with the HMF application. Furthermore, this columnar crystal changed to columnar stack of spherical nanoparticles with the increase of evaporation temperature under HMF. HMF induced a part of the c-axis preferred orientation in the Co films aligning along the direction of HMF. The varied growth structure and preferred orientation led to the change from the in-plane magnetic anisotropy (without HMF) to isotropy in the Co films due to the application of HMF at a higher evaporation temperature. The saturation magnetization of the Co films with columnar crystals obtained by HMF was much larger than that of the films composed of spherical nanoparticles because of the dense atom arrangement. The decrease of the grain boundaries due to the changed growth structure under HMF remarkably reduced the coercivity and resistivity of the Co films. The changed growth structure under HMF also induced and improved the in-plane anisotropic magnetoresistance of the Co films. These results indicate that the adjustment of columnar growth structure by HMF effectively control and improve the soft magnetic and electrical transport properties of the Co films. [ABSTRACT FROM AUTHOR]

In order to distinguish the contribution of various chemical states in the Co-doped ZnO film on the ferromagnetism, the films were prepared by oxidizing as-deposited Co-Zn films fabricated by molecular beam vapor deposition method. Different growth modes of multilayer, co-deposition, and bilayer of the Co-Zn films and oxidization temperature of 300 or 600 °C were used to control the cobalt states of Co metal, cobalt oxide, Co ion in the ZnO lattice and the defects of oxygen vacancy in the films. The insufficient oxidization at 300 °C leads to the aggregation of Co metal. The Co metal features ferromagnetism in the films of the three growth modes. After the films oxidized at 600 °C, the Co ions are predominant in the co-deposition film. The oxygen vacancies are predominant for the bilayer film. Meanwhile, a small amount of cobalt oxide is formed in the co-deposition films. However, no ferromagnetism is observed at room temperature for all the films oxidized at 600 °C. This means that the cobalt oxide, Co ion, and oxygen vacancy cannot improve the RT ferromagnetism. When the measurement temperature decreases to − 150 °C, the ferromagnetism appears in the bilayer film due to the oxygen vacancy. The weak magnetism presents in the co-deposition film because of the Co ions indicating that the oxygen vacancy is more significant in obtaining ferromagnetism than the Co ions. [ABSTRACT FROM AUTHOR]

Room temperature ferromagnetism (RTFM) is detected in the Co doped ZnO films, which are formed via the thermal oxidation of electrodeposited Co/Zn bilayers. The effect of oxidation temperature on the origin of RTFM is examined. Results indicate that various contents of Co 2+ dopants, Zn x Co 3−x O 4 clusters, O vacancy and Zn interstitial are achieved in the films oxidized at 400 and 550 °C. The amount of O vacancy decreases sharply with increasing oxidation temperature. This leads to the saturation magnetization of films oxidized at 400 °C is higher than that of films oxidized at 550 °C. This indicates that the effect of O vacancy on ferromagnetism is more prominent in the Co doped ZnO films. [ABSTRACT FROM AUTHOR]

In this work, structural, electronic and magnetic properties of Ni doped ZnO nanoparticles (NP's) synthesized via the sol-gel method have been investigated. Different techniques of characterization have been applied to study the Ni dependence of the microstructural, morphological, compositional and magnetic properties. As a result, X-ray diffraction analysis indicates that the obtained samples have a hexagonal Wurtzite structure with preferential orientation along (101). The increase of Ni concentration leads to a size reduction of the nanoparticles. Also segregated Ni clusters have been observed by SEM/EDX. The magnetization field (M − H) curves reveal the existence of ferromagnetism in Ni-doped ZnO at room temperature. First principle calculations based on density functional theory are applied to study the effect of Ni doping on the structural, electronic and magnetic properties of ZnO, allowing for a deeper understanding for the experimental findings. The obtained results indicate that Ni doped ZnO with less than 8.33% Ni present long-range ferromagnetic ordering. Furthermore, Ni doped ZnO is antiferromagnetically stable at 12.5%. Monte Carlo simulation based on heat bath algorithm coupled with DFT results have been used to validate the proposed explanation for the magnetic behavior of the experimental part. Therefore, the obtained results indicate that Ni doped ZnO is a good candidate as a diluted magnetic semiconductor due to its high exchange coupling interaction that leads to a high Curie temperature. • Magnetic properties of Ni doped ZnO NP's have been explored experimentally and theoretically. • Reduction of the crystallite size has been observed. • Ni doped samples exhibit ferromagnetic properties at room temperature. • Ni doped ZnO with less than 8.33% of dopant presents a long-range magnetic ordering. • Monte Carlo simulation shows that Ni doped ZnO presents a Curie temperature above the room temperature. [ABSTRACT FROM AUTHOR]