Tuning magnetic properties,thermal stability and microstructure of NdFeB magnets with diffusing Pr-Zn films

Grain boundary diffusion process(GBDP) serves as a promising approach in improving magnetic properties and thermal stability of Nd FeB permanent magnets. Herein, non-heavy rare earth Pr-Zn films deposited on the magnet surface using DC-magnetron sputtering system are reported. The thermal stability and coercivity enhancement mechanism of Pr-Zn GBDP magnets were investigated. Results show that the coercivity of Pr-Zn GBDP magnet increases from 963.96 kA m~(-1) to 1317.14 kA m~(-1) without any remanence reduction. Notably, the demagnetization curve of Pr-Zn GBDP magnet still remains a high squareness ratio. The temperature coefficient of coercivity and anti-demagnetization ability of Pr-Zn GBDP magnet under high temperatures are improved after GBDP treatment. The well-optimized rare earth-rich(RE-rich) grain boundary phases and high effective anisotropy field of(Nd,RE)2 Fe14 B magnetic hardening layers surrounding main grains are the key factors to impact the magnetic properties and thermal stability of Nd FeB permanent magnets via GBDP treatment.     

Magnetic properties and thermal stability of CoFeNi-based amorphous films

CoNiFe-based amorphous films were magnetron-sputtered to investigate their structural and magnetic properties, including annealing-induced effects and interfacial influence from additional layers of Ta and Cu. The amorphous structure was confirmed by diffraction experiments. The magnetic measurements showed a well-defined uniaxial anisotropy in plane, arising possibly from atom oblique incidence effects competing with the stray field of the magnetron. The anisotropy could be influenced by using a Ta buffer layer, though the interfacial reaction gives rise to a dead layer. A coercive force H _c of 1–2 Oe and a magnetization of 680 emu/cm³ were measured at room temperature; properties which show promise for application in magnetotunneling junction devices. Thermal analyses showed a two-stage crystallization behavior, which started at 400°C and ended at about 600°C. The Curie temperature of the amorphous phase was estimated to be about 440°C.     

Sputtering of FeCo-B amorphous films with soft magnetic properties

Microstructures, optimum sputtering conditions, and annealing methods were investigated for the purpose of obtaining zero magnetostriction amorphous films with good magnetic softness. Sputtering conditions which suppress formation of columnar structure in films were studied, and films with high density were obtained. The mechanism of columnar structure suppression is discussed. Annealing in an ellipitically rotating field is effective to reduce in-plane anisotropy and Barkhausen-type noise, and to obtain very weak anisotropy for high initial permeability. Some of the samples thus obtained exhibit excellent softness with high initial permeability.     

Mechanical properties and thermal stability of nitrogen incorporated diamond-like carbon films

The nitrogen incorporated diamond-like carbon films were deposited on Si (100) substrates by arc ion plating (AIP) under different N₂ content in the gas mixture of Ar and N₂. The influence of N₂ content on the film microstructure and mechanical properties was studied by atomic force microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and nanoindentation. It was found that the hardness (H), elastic modulus (E), elastic recovery (R) and plastic resistance parameter (H/E) decrease with increasing the nitrogen content. The decrease of mechanical properties of DLC films resulted from nitrogen incorporation was associated with total sp³ carbon bond content and N-sp³C bond content. The structural modification as well as mechanical properties of the annealed nitrogen incorporated diamond-like carbon films was investigated as a function of annealing temperature. Raman spectra indicate that the I_D/I_G ratio starts to increase and G peak position shifts upward at the annealing temperature over 500 °C. The hardness and elastic modulus of thermally annealed nitrogen incorporated DLC films decreased slightly at lower annealing temperature and then significantly decreased at higher annealing temperature. The strong covalent bonding between C and N atoms is expected to be effective on their thermal stability enhancement.     

Structure, hardness and thermal stability of TiAlN and nanolayered TiAlN/CrN multilayer films

TiAlN films were deposited on silicon (1 1 1) substrates from a TiAl target using a reactive DC magnetron sputtering process in Ar+N₂ plasma. Films were prepared at various nitrogen flow rates and TiAl target compositions. Similarly, CrN films were prepared from the reactive sputtering of Cr target. Subsequently, nanolayered TiAlN/CrN multilayer films were deposited at various modulation wavelengths (Λ). X-ray diffraction (XRD), energy dispersive X-ray analysis, nanoindentation and atomic force microscopy were used to characterize the films. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of TiAlN/CrN multilayers was 3900 kg/mm², whereas TiAlN and CrN films exhibited maximum hardnesses of 3850 and 1000 kg/mm², respectively. Thermal stability of TiAlN and TiAlN/CrN multilayer films was studied by heating the films in air in the temperature range (T_A) of 500-900 °C for 30 min. The XRD spectra revealed that TiAlN/CrN multilayers were stable up to 800 °C and got oxidized substantially at 900 °C. On the other hand, the TiAlN films were stable up to 700 °C and got completely oxidized at 800 °C. Nanoindentation measurements performed on the films after heat treatment showed that TiAlN retained a hardness of 2200 kg/mm² at T_A=700 °C and TiAlN/CrN multilayers retained hardness as high as 2600 kg/mm² upon annealing at 800° C.     

稀土Nd掺杂FeCo纳米磁性薄膜的结构和磁性

利用射频磁控共溅射方法,通过改变Nd靶溅射功率,制备了一系列Ta/Ndx(FeCo)100-x/Ta纳米薄膜。研究了其结构和磁性随Nd含量和真空磁场退火温度(T)的变化关系。X射线衍射研究表明制备态的薄膜为非晶态,随着退火温度的升高,逐渐析出Fe-Co纳米晶,随T的进一步升高,FeCo纳米晶粒逐渐变大,而且在薄膜中生成了FeCoNd合金纳米晶。利用振动样品磁强计研究了纳米薄膜的静态磁性,结果表明,饱和磁化强度随着Nd含量的升高而降低。经真空磁场热处理的样品都表现出很好的面内磁各向异性,在Ta/Nd20(FeCo80)/Ta样品中获得了易轴矫顽力135.32A/m,难轴矫顽力为199A/m,各向异性场为8166.96A/m的优异静态磁性,表明在高频领域具有很好的潜在应用前景。     

溅射法制备Mn-Zn铁氧体薄膜的磁性与微结构

以交替真空溅射的方法使用成分分别为MnFe2O4与ZnFe2O4的双靶制备了成分变化的系列Mn1-xZnxFe2O4铁氧体薄膜,衬底为Si(100)。薄膜的成分通过控制不同靶的溅射时间来进行调整。沉积态的薄膜呈非晶结构,在真空炉中以适当的温度对薄膜进行退火之后能够得到多晶Mn-Zn铁氧体薄膜。组成成分为Mn0.5Zn0.5Fe2O4的薄膜呈现了相对最高的饱和磁化强度。同时还研究了制备条件对薄膜结构与磁性的影响,如溅射氧分压,退火真空度,退火温度及薄膜厚度等等。制备的薄膜相对于块状材料具有较高的矫顽力,进而讨论了应力对薄膜矫顽力的影响。     

Magnetic properties and thermal stability of Co-TM-Zr (TM=Nb,Ta, Mo,W, and Ni) amorphous sputtered films for magnetic heads

The magnetic properties and thermal stability Co-TM-Zr (TM=Nb, Ta, Mo, W, and Ni) amorphous films prepared by rf diode sputtering are investigated. Amorphous films with a homogeneous structure and coercive force H _c of less than 20 A m^–1 are obtained at an argon gas pressure of 0.3–1 Pa. The formation range of the amorphous films is broad in the systems containing Ta and Nb, whereas it is limited to the composition range greater than 4–5 at % of Zr in the systems of Mo, W, and Ni. The magnetostriction _s depends on the concentration ratio of Zr and the TM. Films with zero _s are obtained at concentration ratios C _zr/C _TM ranging from 0.3 for Co-Nb-Zr films to 1.5–1.7 for Co-W-Zr films. The crystallization temperature T _x is highest in Co-Ta-Zr films and lowest in Co-Mo-Zr films when _s is zero and both films have the same saturation magnetic flux density B _s . The anisotropy field H _k is highest in Co-Ni-Zr films and lowest in Co-Nb-Zr films. These results indicate that Co-Ta-Zr and Co-Nb-Zr amorphous films are suitable for use as magnetic head materials because of the Co-Ta-Zr film's high T _x and B _s , and the Co-Nb-Zr film's small ns and low H _K      

超薄纳米晶Zr-N扩散阻挡性能及其热稳定性的研究

用射频反应磁控溅射的方法在Si(100)衬底和Cu膜间制备了25nm的纳米晶Zr-N阻挡层,Cu/Zr-N/Si样品在高纯氮气保护下退火至700℃.用四探针电阻测试仪(FPP)、AFM、SEM、XRD、AES研究了溅射参数对Zr-N薄膜电阻率和扩散阻挡性能的影响.实验结果表明,N2分压从20%增加到25%,电阻率快速增高;溅射偏压不同,Zr-N的结构可由非晶态结构转变为纳米晶.纳米晶Zr-N阻挡层650℃退火1h后仍能有效地阻止Cu的扩散.     

Investigation of thermal stability, phase formation, electrical, and microstructural properties of sputter-deposited titanium aluminide thin films

Titanium aluminide thin films are being considered as coating materials for high temperature applications due to their high melting points and high oxidation resistance. In this study, Ti₃₇Al₆₃ and Ti₅₃Al₄₇ thin films are deposited onto SiO₂ substrates by RF magnetron sputtering using compound targets and then annealed in vacuum to investigate the properties of the films. Rutherford backscattering spectrometry, X-ray diffractometry, transmission electron microscopy, and four-point probe measurements are used to analyze the characteristics of Ti₃₇Al₆₃ and Ti₅₃Al₄₇ thin films for high temperature electronics applications. The films show good thermal stability up to 700 °C for 1 h in vacuum. Reasonable resistivity is obtained when appropriate compositions and anneal conditions are used.     

Structure and magnetic properties of soft organic ZnAl-LDH/polyimide electromagnetic shielding composites

The imidization mechanism, structure, and magnetic properties of organic modified Zinc-aluminum layered double hydroxides/polyimide composites are investigated. During imidization, organic modified Zinc-aluminum layered double hydroxides lose the hydroxyl group and sodium dodecyl sulfate modifier decomposes partly resulting in a loose contact between PI and oxidized Zinc-aluminum layered double hydroxides. The thermal properties of composites are slightly decreased with increasing organic modified Zinc-aluminum layered double hydroxides but the wettability varies oppositely. Comparing to organic modified Zinc-aluminum layered double hydroxides, the saturated magnetization of heated organic modified Zinc-aluminum layered double hydroxides is enhanced slightly due to structural improvement in Fe₃O₄ crystalline domain. Therefore, the magnetic properties are not affected by imidization procedure. The soft magnetic composites have large potential in electromagnetic shielding.     

Mechanical and thermal properties of physical vapour deposited alumina films Part I Thermal stability

Thermal stability of non-reactive physical vapour deposited alumina films of varying thickness on Al₂O₃-TiC and Si substrates, deposited at two different substrate biases, is examined. Substrate curvature measurements were used to determine the deposition stress and stress development during thermal cycling and annealing. Thermal cycling experiments revealed that the films deposited on Al₂O₃-TiC substrates become irreversibly more compressive on heating and annealing while films deposited on Si substrates become irreversibly more tensile. The deposition stress was found to be independent of film thickness, substrate material, and substrate bias during deposition. The thermal stability was independent of film thickness and substrate bias during deposition.     

Effect of the carboxylic acid groups on water sorption, thermal stability and dielectric properties of polyimide films

Films from copolyimides containing side carboxylic acid groups were prepared in -COOH and COO⁻Na⁺ forms to study the effect of the side groups content on some physical properties such as water absorption, thermal stability and electrical parameters. The thermal stability was evaluated by TGA and the results showed that degradation temperatures depended not only on the side groups content but also on the membrane ionic form. This dependence was also observed in the water sorption isotherms; the polyimides with the highest -COOH content showing the highest water sorption in the equilibrium. Dielectric impedance measurements revealed how the side groups and their ionic form affect the material electrical characteristics, in such a way that resistivity decreased and permittivity increased on introducing more -COOH groups in the polymer, which is also related to a higher water uptake of the films.     

Dynamics of domains and walls in soft magnetic films

General equations are derived to describe the simultaneous nonuniform planar rotations of the magnetization vector and displacements of curved domain walls and their junctions in soft magnetic films. These equations take into account effects of exchange stiffness, magnetic anisotropy, external and either long- or short-range demagnetizing fields, wall energy, and dissipation. The case of a matched film pair using the capacitor or transmission-surface approximation for its short-range demagnetizing energy is considered. The theory is founded on energy and dissipation functionals including domain and wall terms. The constraint of wall-normal magnetization continuity across a domain wall is handled by a method of implementing d'Alembert's virtual work principle without introducing Lagrange multipliers. The result is a set of coupled equations expressing the dynamic torque balance at points inside domains, the wall-domain constraint due to wall-normal magnetization continuity, an additional boundary condition coupling domain magnetization and wall curves, and the wall velocity.<>     

Structure, magnetic and thermal properties of Gd2MnTiO6

A new perovskite compound Gd₂MnTiO₆ was synthesized and its crystal structure, magnetic and thermal properties have been investigated. The XRD patterns were refined by the Rietveld method and the refined lattice parameters with the monoclinic space group P2₁/n (No. 14) were a=0.5398 (2), b=0.5704 (2), c=0.7767 (2) nm and β=89.68 (2)°. The antiferromagnetic behavior was observed below 16.0 K and λ-type heat capacity was measured near this temperature.     

Structure and magnetic properties of nanostructured Pd-Fe thin films produced by pulse electrodeposition

Nanostructured Pd-Fe thin films with varied Fe content were prepared by electrodeposition technique from organic electrolytes on Cu and brass substrates. The structure and the magnetic properties of the films were investigated prior to post-deposition annealing. The structure of the Pd1-xFe(x) thin film with x = 0.14, 0.24, and 0.52 was determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM) as a solid solution of iron in palladium face-centered cubic lattice with the (111) orientation of nanograins relatively to the substrate surface. The films with higher iron concentration, x = 0.74, 0.91, have structure of a solid solution based on the body-centered cubic lattice. The average grain size determined by the scanning electron microscopy (SEM) for the first two alloys is 7-10 nm, and for the latter ones it is about 120 nm. The saturation magnetization of the films has linear dependence on the iron content, but coercivity has non-monotonic dependence on x, i.e., the films with x = 0.68 show highest coercivity. The magnetic anisotropy of the samples is studied by ferromagnetic resonance (FMR) spectroscopy.     

Electrical,electromechanical and thermal properties of thin tellurium films

Thin films of tellurium of wide range of thicknesses have been deposited by vacuum evaporation and their electrical properties such as electrical resistivity and temperature coefficient of resistance have been measured. The suitability of these films for possible use as strain gauges has been studied and their strain resistivity behaviour is presented. The thermal conductivity of these films have been determined and these results are presented alongwith. An interesting phenomenon has been noticed. In all these effects an extraordinary behaviour is observed at a specific thickness. This smears out with an increase in the thickness of the film. These effects are explained in terms of size effects in thin films.     

Effect of nitrogen addition on the properties and thermal stability of fluorinated amorphous carbon films

Continuous fluorinated amorphous carbon (a-C : F) films doped with nitrogen (a-C : F : N) were deposited by plasma enhanced chemical vapor deposition using CF₄ and C₂H₂ gases as precursors with the addition of N₂ gas. The surface morphologies, chemical compositions, deposition rates, thermal stability and mechanical properties of these films varied with the deposition parameters, including CF₄ and N₂ feed gas concentrations, processing pressure, plasma power and substrate temperature. With increasing N₂ feed gas concentration, the nitrogen content of the a-C : F : N films increased to about 6 at.% and contributed to higher mechanical properties. After thermal annealing, the a-C : F films with higher fluorine contents exhibited more obvious fluorine release and extensive film thickness shrinkage, whereas the a-C : F : N films with higher contents of nitrogen doping yielded less composition variations, smaller thickness shrinkages, higher mechanical properties, and conclusively better thermal stability.