Growth of crystalline/amorphous biphase Sm-Fe-Ta-N magnetic nanodroplets

Thin films of biphase (amorphous/crystalline) magnetic Sm-Fe-Ta-N nanodroplets were fabricated at room temperature with 157 nm pulse laser deposition in nitrogen from a Sm_13.8Fe_82.2Ta_4.0 target. The 50-100 nm biphase spherical nanodroplets consist of a 5-10 nm internal crystal portion surrounded by the external amorphous phase. Nitrogen fixation in the nanodroplets occurred in the plume. The films exhibit a ferromagnetic response of 2.5 kOe coercivity at room temperature. With further annealing and thermal treatment in nitrogen, the coercivity was increased to 5.0 kOe. The surrounding amorphous layer prevents post-ablation oxidization of the crystalline magnetic nucleus of the nanodroplet.     

Hyperfine interaction in amorphous ferromagnetic cobalt-phosphorous-alloys measured by inelastic scattering of neutrons

The hyperfine interaction at the cobalt nucleus in amorphous ferromagnetic cobalt-phosphorous-alloys CoP _x has been investigated by measuring the inelastic incoherent spin-flip scattering of neutrons. A neutron spectrometer of an extremely high energy resolution of 67 MHz full width at half maximum (FWHM) was used. It was found that the magnetic hyperfine splitting, in first order, is proportional to the magnetic moment of the cobalt atom and that there is a distribution of hyperfine fields of about 50 MHz around a mean value which depends on the phosphorous concentration.

     

SiOx precipitate composition in Si,revisited: Discussion closed?

The composition SiO_x of oxide precipitates in Si has been discussed for the past thirty years with experimentally estimated x ‐values ranging between 1 and 2. It is shown that this spread of x ‐values can be explained by calculating the average composition taking into account temperature and anneal time dependent size and shape of the precipitates and the limitations and probing volumes of the various characterization techniques. Hereby it is assumed that the oxygen‐rich (SiO₂?) core of the precipitates is surrounded by a 2 nm thin SiO layer as revealed by recent electron energy loss spectroscopy analyses. For plate‐like precipitates thinner than and for octahedral precipitates smaller than 6 nm, x ≈ 1. For larger precipitates, the central part of the precipitate consists of SiO_x with x close to 2 and the precipitate has an average x between 1 and 1.3 for plate‐like and up to 1.9 for octahedral precipitates. The predicted x ‐values for different precipitate sizes and morphologies, are compared with published experimental data. SiO_x precipitate nucleation and initial growth should be simulated assuming x = 1 and Fourier transform infrared spectra of precipitates assuming a mixture of SiO₂ and amorphous Si. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Anomalous ferromagnetic resonance in manganese- and aluminum-doped germanium layers deposited from the laser plasma

Ferromagnetic resonance (FMR) with an anomalous angular dependence has been observed in the Ge:(Mn, Al)/GaAs nanolayers deposited from laser plasma at a reduced temperature of 150°C. The resonance is associated with the needle-like inclusions of a high-temperature ferromagnetic phase with the Curie temperature T _C > 293 K. Such a magnetic anisotropy is confirmed by the atomicforce and magneticforce microscopy of a side chip. A low-temperature ferromagnetic phase with normal FMR and T _C < 212 K is formed between the needle-like inclusions. This phase manifests itself in the anomalous Hall effect at 77 K and probably is a solid solution of manganese in germanium.

     

Effective anisotropy field variation of magnetite nanoparticles with size reduction

Size effect on the internal magnetic structure has been investigated on weakly interacting magnetite (Fe₃O₄) nanoparticles by ferromagnetic resonance experiments at 9.5 GHz as a function of temperature (4–300 K). A set of three samples with mean particle size of 2.5 nm, 5.0 nm and 13.0 nm, respectively, were prepared by chemical route with narrow size distribution (σ < 0.27). To minimize the dipolar interaction, the particles were dispersed in a liquid and a solid polymer matrix at ∼0.6% in mass. By freezing the liquid suspension with an applied external field, a textured was obtained. Thus, both random and textured suspensions were studied and compared. The ferromagnetic resonance experiments in zero-field-cooled and field-cooled conditions were carried out to study the size effect on the effective anisotropy field. The dc magnetization measurements clearly show that the internal magnetic structure was strongly affected by the particle size.     

EPR/FMR Investigation of Mn-Doped SiCN Ceramics

SiCN magnetic ceramics doped with Mn²⁺ ions were synthesized at the pyrolysis temperature of 1,100° C, using CERASET™ as liquid polymer precursor and polymer manganese(II) acetylacetonate as dopant, and investigated by electron paramagnetic resonance (EPR)/ferromagnetic resonance (FMR) technique. The predominant source of ferromagnetism in SiCN samples doped with Mn ions, as synthesized here, is the ensemble of ferromagnetic nanoparticles of Mn₅Si₃C _x incorporated into the amorphous SiC/Mn structure. The fluctuation of magnetization due to ferromagnetic Mn₅Si₃C_x particles significantly broadens the EPR lines at the phase-transition temperature (363 K). This is the first fabrication of a SiCN/Mn ceramic, which exhibits room-temperature ferromagnetism.     

Possible reconstruction of the ferromagnetic state under the influence of superconductivity in epitaxial V/Pd1−x Fe x bilayers

Epitaxial V/Pd_1−x Fe _x (001) bilayers with a V thickness of the order of 40 nm and with a Pd_1−x Fe _x thickness in the range from 0.8 nm to 4.4 nm were prepared by molecular beam epitaxy techniques. The Curie temperature of the Pd_1−x Fe _x layers varies between 90 and 250 K. For a bilayer with a Pd_1−x Fe _x thickness of 1.2 nm the ferromagnetic resonance measurements revealed a decrease of the effective magnetization 4πM _eff of the ferromagnetic layer below the superconducting transition temperature of V. As a possible explanation for this decrease we suggest a spatial modulation of the ferromagnetic order in the Pd_1−x Fe _x layer due to modifications of the indirect exchange interaction of magnetic ions via conduction electrons in the superconducting state. A comparison with a recent theoretical investigation supports this possibility.     

Ferromagnetic resonance, magnetic properties, and resistivity of (CoFeZr)x(Al2O3)1 ? x/Si multilayer nanostructures

Comparative investigations of static magnetic properties, magnetoresistance, and ferromagnetic resonance data of multilayer nanostructures consisting of CoFeZr-Al₂O₃ composite magnetic layers and amorphous silicon semiconductor spacers were performed in a layer thickness range below 5 nm. The influence of layer dimension parameters and chemical peculiarities of silicon on the inner structure and type of magnetic interactions in nanostructures with 35 and 46 at % magnetic phase composite layers is discussed.     

Structural and electrical properties of tantalum nitride thin films fabricated by using reactive radio-frequency magnetron sputtering

TaN thin film is an attractive interlayer as well as a diffusion barrier layer in [FeN/TaN]_n multilayers for the application as potential write-head materials in high-density magnetic recording. We synthesized two series of TaN films on glass and Si substrates by using reactive radio-frequency sputtering under 5-mtorr Ar/N₂ processing pressure with varied N₂ partial pressure, and carried out systematic characterization analyses of the films. We observed clear changes of phases in the films from metallic bcc Ta to a mixture of bcc Ta(N) and hexagonal Ta₂N, then sequentially to fcc TaN and a mixture of TaN with N-rich phases when the N₂ partial pressure increased from 0.0% to 30%. The changes were associated with changes in the grain shapes as well as in the preferred crystalline orientation of the films from bcc Ta [100] to [110], then to random and finally to fcc TaN [111], correspondingly. They were also associated with a change in film resistivity from metallic to semiconductor-like behavior in the range of 77–295 K. The films showed a typical polycrystalline textured structure with small, crystallized domains and irregular grain shapes. Clear preferred (111) stacks parallel to the substrate surface with embedded amorphous regions were observed in the film. TaN film with [111]-preferred orientation and a resistivity of 6.0 mΩ cm was obtained at 25% N₂ partial pressure, which may be suitable for the interlayer in [FeN/TaN]_n multilayers. Received: 6 December 1999 / Accepted: 24 July 2000 / Published online: 9 November 2000     

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.     

Magnetism of nanocrystalline Finemet alloy: experiment and simulation

Mössbauer spectrometry and magnetic measurements are employed to experimentally investigate the magnetic behavior of nanocrystalline Fe_73.5Cu₁Nb₃Si_13.5B₉ ribbons obtained by appropriate annealing of the amorphous precursor. A detailed analysis of the correlation between the microstructure of annealed samples and their magnetic properties is provided. Thermomagnetic data allow the Curie temperatures of both amorphous residual matrix and nanocrystalline phase to be estimated. The differences between Curie temperatures of amorphous residual matrix and amorphous precursor are investigated and explained in terms of magnetic polarization of the matrix by exchange fields arising from the nanocrystalline grains. Theoretical systems of spins consisting of a single ferromagnetic nanocrystalline grain immersed in weakly ferromagnetic environment, quite similar to our real samples, are considered and their magnetic behavior is investigated by Monte Carlo simulation of low temperature spin ordering, with emphasize on the matrix-nanocrystalline grain interface which is shown to exhibit peculiar magnetic behavior. The magnetic features of the matrix-nanocrystalline grain interface are studied, as depending on matrix-nanocrystalline grain exchange coupling as well as crystalline fraction of the nanocrystalline systems.Received: 10 April 2003, Published online: 4 August 2003PACS: 81.07.Bc Nanocrystalline materials - 75.30.-m Intrinsic properties of magnetically ordered materials - 75.75.+a Magnetic properties of nanostructures     

Effect of electric current on the magnetic and magnetoelastic properties of amorphous ferromagnetic alloys

The magnetic and magnetoelastic parameters of Fe₆₄Co₂₁B₁₅ and Fe_81.5B_13.5Si₃C₂ amorphous ferromagnetic alloys treated by direct electric current in air are studied as functions of the applied magnetic field and current density. The samples of the alloy have the form of narrow strips with different lengths. It is found that the magnetoelastic parameters of the dc-treated alloys depend on the magnetic field in a qualitatively different way. From the behavior of the magnetic and magnetoelastic parameters of the alloys in the magnetic field a model of magnetization nonuniform distribution in amorphous ferromagnetic alloys subjected to dc treatment is proposed.     

Ferromagnetism in amorphous Ge1−xMnx grown by low temperature vapor deposition

Magnetic properties of amorphous Ge_1−xMn_x thin films were investigated. The thin films were grown at 373 K on (100) Si wafers by using a thermal evaporator. Growth rate was ∼35 nm/min and average film thickness was around 500 nm. The electrical resistivities of Ge_1−xMn_x thin films are 5.0×10⁻⁴∼100 Ω cm at room temperature and decrease with increasing Mn concentration. Low temperature magnetization characteristics and magnetic hysteresis loops measured at various temperatures show that the amorphous Ge_1−xMn_x thin films are ferromagnetic but the ferromagnetic magnetizations are changing gradually into paramagnetic as increasing temperature. Curie temperature and saturation magnetization vary with Mn concentration. Curie temperature of the deposited films is 80-160 K, and saturation magnetization is 35-100 emu/cc at 5 K. Hall effect measurement at room temperature shows the amorphous Ge_1−xMn_x thin films have p-type carrier and hole densities are in the range from 7×10¹⁷ to 2×10²² cm⁻³.     

Correction: Ab initio study of anisotropic mechanical and electronic properties of strained carbon-nitride nanosheet with interlayer bonding

The magnetic and electronic properties of strontium titanate with different carbon dopant configurations are explored using first-principles calculations with a generalized gradient approximation (GGA) and the GGA+U approach. Our results show that the structural stability, electronic properties and magnetic properties of C-doped SrTiCO₃ strongly depend on the distance between carbon dopants. In both GGA and GGA+U calculations, the doping structure is mostly stable with a nonmagnetic feature when the carbon dopants are nearest neighbors, which can be ascribed to the formation of a C-C dimer pair accompanied by stronger C-C and weaker C-Ti hybridizations as the C-C distance becomes smaller. As the C-C distance increases, C-doped SrTiCO₃ changes from an n-type nonmagnetic metal to ferromagnetic/antiferromagnetic half-metal and to an antiferromagnetic/ferromagnetic semiconductor in GGA calculations, while it changes from a nonmagnetic semiconductor to ferromagnetic half-metal and to an antiferromagnetic semiconductor using the GGA+U method. Our work demonstrates the possibility of tailoring the magnetic and electronic properties of C-doped SrTiO₃, which might provide some guidance to extend the applications of strontium titanate as a magnetic or optoelectronic material.

     

Frustrated exchange interactions formation at low temperatures and high hydrostatic pressures in La<Subscript>0.70</Subscript>Sr<Subscript>0.30</Subscript>Mn<Subscript>O2.85</Subscript>

The magnetic and thermal properties of the anion-deficient La_0.70Sr_0.30MnO_2.85 manganite are investigated in wide temperature (4–350 K) range, including under hydrostatic pressure (0–1.1 GPa). Throughout the pressure range investigated, the sample is spin glass with diffused phase transition into paramagnetic state. It is established, that spin glass state is a consequence of exchange interaction frustration of the ferromagnetic clusters embeded into antiferromagnetic clusters. The magnetic moment freezing temperature T _f of ferromagnetic clusters increases under pressure, freezing temperature dependence on pressure is characterized by derivative value ∼4.5 K/GPa, while the magnetic ordering T _MO temperature dependence is characterized by derivative value ∼13 K/GPa. The volume fraction of sample having ferromagnetic state is V _fer ∼ 13% and it increases under a pressure of 1.1 GPa by ΔV _fer ≈ 6%. Intensification of ferromagnetic properties of the anion-deficient La_0.70Sr_0.30MnO_2.85 manganite under hydrostatic pressure is a consequence of oxygen vacancies redistribution and unit cell parameters decrease. The most likely mechanism of frustrated exchange interactions formation is discussed.     

Tuning magnetic fingerprints of FeNi nanowire arrays by varying length and diameter

Magnetic nanowires (NWs) electrodeposited into solid templates are of high interest due to their tunable properties which are required for magnetic recording media and spintronic devices. Here, highly ordered arrays of FeNi NWs with varied lengths (ranging from 2.5 to 12 μm) and diameters (between 45 and 75 nm) were fabricated into anodic aluminum oxide templates using a pulsed ac electrodeposition technique. X-ray diffraction patterns along with energy dispersive spectroscopy indicated the formation of Fe₇₀Ni₃₀ NWs with fcc and bcc alloy phases, being highly textured along the bcc [110] direction. Magnetic properties were studied by hysteresis loop measurements at room temperature and they showed reductions in coercivity and squareness values by increasing length and diameter. Further, magnetic fingerprints of the NWs were characterized using the first-order reversal curve (FORC) analysis. FORC measurements revealed that, with increasing length and diameter from 2.5 to 10 μm and 45–55 nm, respectively, besides an increase in inter-wire magnetostatic interactions, a transition from a single domain (SD) state to a pseudo SD state occurred. Moreover, a multi-domain (MD) state was found for the longest length and diameter. While the irreversible magnetization component of the SD NWs was approximately 100%, the reversible component of MD NWs increased up to 20%.     

Magnetic properties of hematite with large coercivity

The magnetic properties of hematite powders produced by a solid state nucleation-and-growth process are studied as a function of temperature T and applied field H. Independently of the temperature, there exists a soft magnetic contribution that is assigned to the canting of spins at the superficial shell of each particle and is not affected by the Morin transition. At 220<T<T _M a magnetic contribution with high coercivity is observed, due to spin–flop in the anti ferromagnetic state and above T _M =248 K the weakly ferromagnetic state has a coercivity that ranges from 6 kOe to 4 kOe when raising T up to room temperature. Different sub-grain structures were obtained by means of isochronal and isothermal annealing. Changes in the susceptibility are directly related to the sub-particle size. It is concluded that sub-boundaries are the defects responsible for the high coercivities observed in the weakly ferromagnetic state.     

Effect of nitrogen concentration on the magnetic properties of Fe-Ta-N thin films

Soft magnetic nanocrystalline thin films with a high content of Ta (10 wt %) are synthesized by the method of reactive RF magnetron sputtering with subsequent annealing. It is established that the microstructure and magnetic properties of the films depend on the nitrogen partial pressure during sputtering and on the annealing temperature. Annealing of the amorphous films leads to the formation of α-Fe nanocrystallites whose properties and interactions determine the film parameters. A decrease in the α-Fe grain size to a level below the length of ferromagnetic exchange interaction sharply increases the magnetic softness. The role of nitrogen ions in the formation of a α-Fe nanocrystallite structure and uniaxial magnetic anisotropy of Fe-Ta-N films is established. The optimum technological regimes of deposition and annealing of the Fe-Ta-N films are determined, which ensure the synthesis of Fe-Ta-N nanocrystalline thin films with a high magnetic softness (B _s=1.6 T, H _c=0.2 Oe, and μ₁(1 MHz)=3400).     

FeCo基纳米晶合金高温交换耦合作用机理

研究了500和600℃真空退火后的纳米晶Fe_38.4Co₄₀Si₉B₉Nb_2.6Cu合金初始磁导率随温度的变化规律,发现较高温度(600℃)退火的FeCo基纳米晶合金,在非晶相居里温度以上较宽温度范围内磁导率没有明显的衰减,这是在双相纳米晶合金中观察到的一种新现象,其磁特性不同于Fe基纳米晶合金.为了探明这种现象的起源,估算了与剩余非晶相同成分的非晶合金的居里温度及纳米晶粒间发生交换耦合作用的参数 关键词： 交换耦合作用 非晶相居里温度 交换耦合穿透深度     

Magnetic properties of amorphous Mn x B100−x alloys

Magnetic properties of amorphous Mn _x B_100–x alloys ranging fromx = 30 to 70 under high magnetic fields and low ac magnetic fields in the temperature range from 4.2 K to room temperature have been investigated. Samples which have Mn concentrations of aboutx = 40–60 show spin-glass-like properties in the low-temperature region. This spin-glass characteristics result from a frustration in the spin system which is caused by the competition of ferromagnetic and antiferromagnetic interactions between randomly distributed Mn atoms. Both magnetization at 4.2 K and paramagnetic momentP _eff as a function of Mn concentration show a peak aroundx 44 which drops rapidly towards both sides of the Mn content.