Ferromagnetic and transport properties of highly Mn-doped ZnSnAs2 epitaxial layers on InP substrates

Ternary ZnSnAs₂ thin films heavily doped with nominal 10 and 20% Mn content on InP (001) substrates are grown using low-temperature molecular beam epitaxy and their magnetic and transport properties are investigated for the first time. It is found that the Mn-doped ZnSnAs₂ thin films are pseudomorphically grown on nearly lattice-matched InP (001) substrates, and a trace amount of secondary phase MnAs formation is observed by high-resolution X-ray diffraction (HR-XRD) measurements. Magnetization measurements on Mn-doped ZnSnAs₂ thin films reveal that the Curie temperature is around 334 K. Nominal magnetic moments per Mn atom measured from the saturation magnetization of hysteresis loops at 5 K have been estimated as 5.28 and 4.17 μ_B for 10% and 20% Mn-doped ZnSnAs₂ thin films, respectively. We have found from Hall effect measurements that the 10% and 20% Mn-doped ZnSnAs₂ films exhibit n-type conduction, in contrast to p-type conduction in ZnSnAs₂ doped with less than 10% Mn. This is likely related to the presence of a certain amount of Mn interstitials or Mn³⁺ substitution on Zn site in the samples.     

Effect of Mn doping concentration on structural,vibrational and magnetic properties of NiO nanoparticles

The Ni_1?xMn_xO (x?=?0.00, 0.02, 0.04 and 0.06) nanoparticles were synthesized by chemical precipitation route followed by calcination at 500?°C for 4?h. The prepared samples were characterized by energy dispersive analysis of X-rays (EDAX), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). Rietveld refinement of XRD data confirms the structural phase purity and XRD patterns are well indexed to NaCl like rock salt fcc crystal structure with Fm-3m space group. The particle size of Mn doped samples is found to be less than that of pure NiO sample. However, the particle size increases slightly on increasing the Mn concentration due to surface/grain boundary diffusion. The vibrational properties of the synthesized nanoparticles were investigated by Raman and FT-IR spectroscopy. The results of room temperature magnetization (M-H) and temperature dependent magnetization (M-T) measurements are explained with a core-shell model. The synthesized nanoparticles show weak ferromagnetic and super-paramagnetic like behavior at room temperature.     

Structural,optical and magnetic characterizations of Mn-doped MgO nanoparticles

Structural, optical and room temperature magnetic properties of Mn-doped MgO nanoparticles with Mn fractions (5–50 at.%), were investigated. The as-prepared pure MgO, with grain size of about 15 nm, exhibits two magnetization components, one is diamagnetic and another is superparamagnetic. After removing the diamagnetic contribution, the magnetization curve exhibits superparamagnetic behavior which may be attributed to vacancy defects. As the Mn content increases, the lattice parameter decreases, the ferromagnetism appears and the emission bands were considerably blue shifted. First principle electronic structure calculations reveal the decrease of both the gap and the Curie temperature with increasing Mn concentration. The obtained results suggest that both Mn doping and oxygen vacancies play an important role in the development of room temperature ferromagnetism.     

Sol-gel synthesis, structure and magnetic properties of Mn-doped ZnO diluted magnetic semiconductors

2.5, 5, 10 and 15% Mn-doped ZnO diluted magnetic semiconductors (DMSs) were prepared via an ethyl acetoacetate-aided sol-gel process. The 5% Mn-doped ZnO consists of 20-50 nm spheroid-like particles and has a wurtzite phase. Existence of nanoscale ZnMnO₃ clusters in this sample is confirmed by HRTEM analysis. Vegard's law calculation reveals that about 2.6% Mn atoms have been incorporated into ZnO lattice. Besides major wurtzite phase, ZnMnO₃ secondary phase is observed in the 10% and 15% Mn-doped samples. The Mn-doped ZnO shows red shift of photoluminescence (PL), which arises from defects caused by Mn incorporation. The magnetic measurements confirm that the 2.5% and 5% Mn-doped ZnO samples display room-temperature ferromagnetism as well as paramagnetism, while the 10% and 15% samples exhibit paramagnetic effects. The as-observed ferromagnetic behaviors likely originate from cooperative effect of intrinsic and extrinsic magnetisms.     

Thin films containing Mn-doped ZnS nanocrystals synthesised by chemical method and study of some of their optical properties

In this article, we present the optical properties of thin films containing Mn-doped ZnS nanocrystals synthesised by the chemical method. The ZnS nanoparticles within the polymer matrix (polyvinyl alcohol) were investigated by SEM and TEM images and analysed by X-ray diffraction. The effect of polymer concentration on the direct band gap of Mn-doped ZnS thin films was calculated from the data for absorption measurements. The values of the band gap are in the range of 3.73–3.90?eV. In addition, we discuss the photoluminescence of these films.     

Structural and magnetic properties of Mn nanoparticles prepared by arc-discharge

Mn nanoparticles are prepared by arc discharge technique. MnO, α-Mn, β-Mn, and γ-Mn are detected by X-ray diffraction, while the presence of Mn₃O₄ and MnO₂ is revealed by X-ray photoelectron spectroscopy. Transmission electron microscopy observations show that most of the Mn nanoparticles have irregular shapes, rough surfaces and a shell/core structure, with sizes ranging from several nanometers to 80 nm. The magnetic properties of the Mn nanoparticles are investigated between 2 and 350 K at magnetic fields up to 5 T. A magnetic transition occurring near 43 K is attributed to the formation of the ferrimagnetic Mn₃O₄. The coercivity of the Mn nanoparticles, arising mainly from Mn₃O₄, decreases linearly with increasing temperature below 40 K. Below the blocking temperature T_B ≈ 34 K, the hysteresis loops exhibit large coercivity (up to 500 kA/m), owing to finite size effects, and irreversibility in the loops is found up to 4 T, and magnetization is not saturated up to 5 T. The relationship between structure and the magnetic properties are discussed.     

具有多层结构的聚合物复合薄膜的介电和磁性能

采用旋涂法制备了 Fe3 O4/聚偏氟乙烯(PVDF)复合薄膜(A)、多壁碳纳米管(MWCNT)/PVDF复合薄膜(B)以及纯PVDF薄膜(P)。利用热压法制备具有3层结构的AAA、ABA及APA 复合薄膜。为了探究层状结构对复合薄膜介电和磁性能的影响,制备了单层膜A作为对比(厚度与AAA复合薄膜相同)。分别研究了薄膜的介电和磁性能。结果表明：由于界面效应,同等厚度的AAA复合薄膜较A膜而言具有较高的介电常数;以B和P薄膜替代AAA结构中间层薄膜后,其中ABA复合薄膜的介电常数高于AAA及APA复合薄膜,同时保持较低的介电损耗。对于磁性能,层状结构对复合薄膜的饱和磁化强度及矫顽力均无明显的影响,而ABA复合薄膜的饱和磁化强度高于AAA及APA复合薄膜,且ABA和APA复合薄膜的矫顽力增加。层状结构设计不仅能够调节复合材料的介电性能和磁性能,而且有利于不同纳米填料的分散,为制备多功能聚合物复合材料提供了一定的借鉴作用。     

Peculiarities of formation and luminescence of ZnS nanoparticles modified with amino acids

Surface modification of ZnS nanoparticles with various amino acids leads to dramatic changes in luminescence: 30-40-fold increase in the case of glycine and methionine and almost total disappearance of luminescence in the case of cysteine. The study of formation of “nacked” and surface-modified ZnS revealed two main stages: quite rapid process of generation of ZnS nanoparticles and relatively slow process of the formation of the luminescent centers. The last are the surface defected zinc ions, capped with amino acid in the case of modified species.     

Room temperature optical and magnetic properties of polyvinylpyrrolidone capped ZnO nanoparticles

Defect induced room temperature ferromagnetic properties of polyvinylpyrrolidone (PVP) capped nanocrystalline ZnO samples have been studied. Crystal phase and the lattice parameter of the synthesized nanocrystalline samples have been determined from X-ray diffraction spectra (XRD) and high-resolution transmission electron micrographs (HR-TEM). Room temperature photoluminescence (PL) spectrum for the bare ZnO sample shows a strong band at ~ 379 nm and another band at ~ 525 nm. The PL spectra also revealed that the number of oxygen vacancies in the uncapped sample is more than the PVP capped sample. Both sample exhibit ferromagnetic property at room temperature when annealed at 500 °C for 3 h, due to the formation of adequate oxygen vacancy related defects. The saturation magnetization for the annealed PVP capped sample is found to be larger compared to that for the uncapped sample.     

Structural and magnetic properties of Co-Ga co-doped ZnO thin films fabricated by pulsed laser deposition

Co-Ga co-doped ZnO films were fabricated by pulsed laser deposition on quartz substrates. The obtained films exhibited a wurtzite structure with c-axes growth preference. Optical measurements showed the presence of the cobalt ions in a tetrahedral crystal field, which proved that the Co ion substitution in the ZnO lattice, acting as magnetic cation. Hall measurements indicated that the films were n-type conductive with the electron concentrations of ~ 10²⁰/cm³. This value was much higher than that of the Co-doped films, suggesting the effective incorporation of Ga in the films. Room temperature ferromagnetism was observed for the Ga-Co co-doped thin films.     

Structure and luminescence properties of Mn-doped Zn2SiO4 prepared with extracted mesoporous silica

Zn₂SiO₄:Mn powders were prepared by solid-state reaction using extracted SBA-15 as silica source. The well crystalline willemite Zn₂SiO₄:Mn can be obtained at 800 °C, much lower than the conventional solid-state reaction temperature and lower than using the calcined SBA-15. This can be attributed to the high reactive activity of the extracted SBA-15 due to its high density silanol groups, large surface areas, and non-crystalline structure. Ultraviolet (UV) and vacuum ultraviolet (VUV) excitation spectra reveal the host lattice absorption band around 162 nm and the charge transfer transition band around 245 nm. The Zn₂SiO₄:Mn phosphor exhibits a strong green emission around 527 nm. The Zn₂SiO₄:Mn phosphor with an Mn doping concentration of 0.06, i.e., Zn_1.94Mn_0.06SiO₄, shows the highest relative emission intensity. Upon 147 nm excitation, the luminescence decay time of the green emission of Zn_1.94Mn_0.06SiO₄ around 527 nm is 8.87 ms.     

Cu-doping effect on structure and magnetic properties of Fe-doped ZnO powders

Fe-doped and Cu, Fe co-doped ZnO diluted magnetic semiconductors powders were synthesized by sol–gel method. The x-ray diffraction (XRD) results showed that Zn_0.97−xFe_0.03Cu_xO (x ≤ 0.02) samples were single phase with the ZnO-like wurtzite structure. X-ray photoelectron spectroscopy (XPS) showed that Fe²⁺ and Fe³⁺ existed in Zn_0.97Fe_0.03O, while Fe²⁺, Fe³⁺and Cu⁺, Cu²⁺ were found in Zn_0.95Fe_0.03Cu_0.02O. Both Zn_0.97Fe_0.03O and Zn_0.95Fe_0.03Cu_0.02O exhibited ferromagnetic performance at room temperature. But the Cu incorporation reduced the saturation magnetization of Fe-doped ZnO diluted magnetic semiconductors.     

Structural,optical, and magnetic properties of polycrystalline Co-doped TiO2 synthesized by solid-state method

We have used a solid-state method to synthesize polycrystalline Co-doped TiO₂ diluted magnetic semiconductors (DMSs) with Co concentrations of 0, and 0.5 at.%. X-ray diffraction patterns reveal that Co doped TiO₂ crystallizes in the rutile tetragonal structure with no additional peaks. Transmission electron microscopy (TEM) did not indicate the presence of magnetic parasitic phases and confirmed that Co ions are uniformly distributed inside the samples. Optical absorbance measurements showed an energy band gap which decreases after doping with the Co atoms into the TiO₂ matrix. Magnetization measurements revealed a paramagnetic behavior for the as-prepared Co-doped TiO₂ and a ferromagnetic behavior for the same samples after annealed under a mixture of H₂/N₂ atmosphere.     

Effects of the stacking levels on permeability characteristics and soft magnetic properties in FeCoHfAlO/AlOx multilayered films

In the communication industry, miniaturization is highly required for inductor devices. In order to miniature the dimension of inductors, high inductance is necessary. For this purpose, to employ high-permeability magnetic films enhances the inductance of inductors. For high-permeability, in-plane uniaxial anisotropy is a critical demand. The FeCoHfAlO/AlO_x multilayered films were fabricated by dc reactive magnetron sputtering. Due to the insertion of AlO_x layers, the out-of-plane uniaxial anisotropy of the FeCoHfAlO magnetic films is reduced and their resistivity is also raised. Therefore, the permeability of the FeCoHfAlO/AlO_x multilayers will be increased further. With the optimum configuration of a seven-layer structure [FeCoHfAlO (171 nm)/AlO_x (10 nm)]₇, high resistivity (ρ ~ 7490 μΩcm) and high-permeability (μ′ > 90 at 30-50 MHz) were obtained. The permeability increased nearly ten times from 9 (3 layers) to 98 (7 layers).     

Improvement of magnetic characteristics and electrical properties of FeCoHfO/AlOx multilayered films

High permeability magnetic films can enhance the inductance of thin-film inductors in DC-DC converters. In order to obtain high permeability, effective uniaxial anisotropic field should be as low as possible. A multilayered technique (laminating the magnetic layers with oxide spacers) was exploited to improve the magnetic properties of thick films. The FeCoHfO/AlO_x multilayered films were fabricated by dc reactive magnetron sputtering. Inserting an insulator (AlO_x) layer can decrease the magneto-elastic anisotropy by reducing the residual stress of the FeCoHfO magnetic films. The anisotropic field and resistivity of the FeCoHfO/AlO_x multilayered films were evidently improved by multilayered coating. With this optimum configuration of 9 layers structure [FeCoHfO (133 nm)/AlO_x (10 nm)]₉, low anisotropic field (H_K = 65 Oe) and high resistivity (ρ ∼ 1350) μΩ cm were achieved.     

多元醇法制备CoNi纳米粒子的形成机制,尺寸控制及磁性能

采用多元醇法在150～190℃合成了CoNi合金纳米粒子,利用SEM-EDX,XRD和VSM对所制备的CoNi纳米粒子形貌、成分、结构以及磁性能进行了研究,并进一步探讨了形核剂K2PtCl4对CoNi纳米粒子形貌及磁性能的影响。结果表明,在180℃用多元醇法制备的Co40Ni60(inat%)纳米粒子为FCC结构,Co2+要易于Ni2+被还原,导致最初10min内合成的CoNi纳米粒子中含有约78%(原子分数)Co,表现为高饱和磁化强度和高矫顽力,随着反应时间的延长,CoNi纳米粒子的Co含量、饱和磁化强度及矫顽力逐步下降。在150～190℃范围内,随着反应温度的提高,Ni2+的被还原能力增强,高温下合成的CoNi纳米粒子具有较低的饱和磁化强度和较小的矫顽力。形核剂K2PtCl4的加入,并不影响CoNi合金纳米粒子的成分和晶体结构。但是,随着形核剂浓度的增加,CoNi纳米粒子平均直径明显减小,其矫顽力有所增大。通过设计形核剂的浓度,CoNi纳米粒子的直径可以在96～580nm范围内任意控制。     

Characterization and magnetic properties of Sm- and Gd-substituted CoFe2O4 nanoparticles prepared by forced hydrolysis in polyol

Pure nanoparticles of the CoFe_2−xRE_xO₄ (RE = Gd, Sm; x = 0.0, 0.1) system have been prepared by forced hydrolysis in polyol. The insertion of Sm³⁺ and Gd³⁺ cations into the cobalt ferrite structure has been investigated. X-ray micro-analysis (EDX) shows that the RE contents are close to the nominal ones. X-ray diffraction (XRD) evidences a cell size increase with slight distortions in the spinel-like lattice indicating the entrance of RE³⁺ ions. Micro-Raman spectroscopy confirms the cubic inverse-spinel structure and rules out the existence of impurities like hematite. Magnetic measurements (SQUID) show important differences in the magnetic properties of the unsubstituted and substituted particles. All the particles are superparamagnetic at room temperature and ferrimagnetic at low temperature. However, their main magnetic characteristics appear to be directly dependent on the RE content.     

Synthesis and photoluminescence properties of Cl-doped ZnS nanoparticles prepared by a solid-state reaction

ZnS:Cl⁻ nanoparticles with strong blue emission have been synthesized successfully by a solid-state reaction at low temperature. The dependence of photoluminescence (PL) properties of ZnS:Cl⁻ nanoparticles on the Cl⁻ contents was researched, and the influences of the annealing ambience and using polyvinyl alcohol (PVA) during the synthesis on the PL of ZnS:Cl⁻ (Cl/Zn = 0.35) nanoparticles were discussed. X-ray power diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and ultraviolet-visible spectroscopy were used to characterize their structure, chemical state, diameter, surface states, and PL properties. The results showed that ZnS:Cl⁻ nanoparticles had a cubic blende crystal structure and an average crystallite size of 17.40–19.16 nm. The most intensity blue emission peaking at about 425 nm was obtained when Cl/Zn = 0.35 under 330 nm excitation at room temperature. The emission intensity of ZnS:Cl⁻ (Cl/Zn = 0.35) was increased 3-fold than that of ZnS. The results showed that the PL of ZnS:Cl⁻ (Cl/Zn = 0.35) nanoparticles was enhanced after annealing or using PVA during the synthesis, and annealing in vacuum had a stronger effect in improving the luminescence properties of ZnS nanoparticles than in air. This work suggests that it is an effective method to improve the PL intensity of ZnS nanocrystals by doping with Cl⁻ in ZnS.     

Morphology control and luminescence properties of YAG:Eu phosphors prepared by spray pyrolysis

Starting from nitrate aqueous solutions with citric acid and polyethylene glycol (PEG) as additives, Y₃Al₅O₁₂:Eu (YAG:Eu) phosphors were prepared by a two-step spray pyrolysis (SP) method. The obtained YAG:Eu phosphor particles have spherical shape, submicron size and smooth surface. The effects of process conditions of the spray pyrolysis on the crystallinity, morphology and luminescence properties of phosphor particles were investigated. The emission intensity of the phosphors increased with increasing of sintering temperature and solution concentration due to the increase of the crystallinity and particles size, respectively. Adequate amount of PEG was necessary for obtaining spherical particles, and the optimum emission intensity could be obtained when the concentration of PEG was 0.10 g/ml in the precursor solution. Compared with the YAG:Eu phosphor prepared by citrate-gel (CG) method with non-spherical morphology, spherical YAG:Eu phosphor particles showed a higher emission intensity.     

Dielectric and magnetic properties of ZnCo-substituted X hexaferrites prepared by citrate sol-gel process

Ba₂Zn_2−xCo_xFe₂₈O₄₆ hexaferrites with x=2.0, 1.6, 1.2, 0.8, 0.4 and 0.0 were prepared by citrate sol-gel process. They were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetry-differential scanning calorimetry (TG-DSC). The frequency-response complex dielectric constant and complex permeability of Ba₂Zn_2-xCo_xFe₂₈O₄₆ sintered at 1000-1200 °C had been investigated in the range from 100 MHz to 6 GHz. The pronounced natural resonance phenomena were observed in μ″ spectrum for the samples annealed at 1100 and 1200 °C. The natural resonance frequency of Ba₂Zn_2−xCo_xFe₂₈O₄₆ ferrites was intensively affected by the substitution of Zinc ion and annealing temperature.