Cr migration in CoNiTa/Cr films by annealing

CoNiTa/Cr double-layered films for longitudinal magnetic recording media have been prepared by using the facing targets sputtering apparatus. Substrate heating and postannealing were performed in order to increase the coercive force H_c. While the as-deposited film at the substrate temperature T_s of 400°C had H_c of 780 Oe, the films deposited at T_s of room temperature, exposed to atmosphere, and annealed at 400°C, had H_c as high as 1700 Oe. It has been found that the same amount of Cr atoms migrated from the underlayer to the magnetic layer and the vicinity of the film surface. Consequently, such a large increase of H_c seemed to be caused by isolation of magnetic grains by Cr atoms in their boundaries     

Development of high-quality ceramic powders for Sr0.9Ca0.1Zn2-W type hexagonal ferrite for permanentmagnet devices

Fine ceramic powders of Sr_0.9Ca_0.1Zn₂ Fe₁₆O₂₇ (Sr_0.9Ca_0.1Zn ₂-W) ferrite, of almost single domain grain size ~1 μm, have been synthesized successfully by sintering for a few hours a mixture of SrCO₃, CaCO₃, ZnO, and α-Fe₂ O₃ in stoichiometric amounts at an effectively low temperature (T_s) of ~1100°C. Carbon dioxide evolves in the reaction Sr(Ca)CO₃+2ZnO+8 α-Fe₂D₃ &lrarr2;Sr(Ca)Zn₂Fe₁₆O₂+C₂ , making fine pores in the sample, which prevent large grain growth of the material and result in a very loose powder. The small ⩽10% substitution of Sr by Ca activates the reaction, but preserves the crystallization of the small-sized grains. This yields magnetic properties useful for most permanent magnet applications, with a promisingly high coercivity H_c~3650 Oe and saturation magnetization M_s~65 emu/g. A considerably better saturation magnetization M_s~85 emu/g can be obtained by sintering the samples at higher T_s~1300°C, but that results in a rather very low coercivity H_c~105 Oe     

Grain size dependence of coercivity and permeability innanocrystalline ferromagnets

Amorphous ribbons of composition Fe_74.5-xCu_xNb₃Si_13.5B₉ (x=0, 1 at.%) have been annealed between about 500°C and 900°C. This produced a series of crystallized samples with grain sizes between about 10 nm and 300 nm and with coercivities H _c and initial permeabilities μ_i varying over several orders of magnitude. The best soft magnetic properties (H _c≈0.01 A/cm and μ_i≈80×10³ ) were observed for the smallest grain sized of about 10 nm. With increasing grain size D, coercivity steeply increases following a D⁶-power law (up to D≈50 nm). H_c then runs through a maximum of H_c≈30 A/cm and decreases again for grain sizes above 150 nm according to the well-known 1/D law for polycrystalline magnets. The initial permeability was found to vary in a similar manner, essentially being inversely proportional to coercivity. The variation of the soft magnetic properties with the average grain size is discussed and compared with the predictions of the random anisotropy model and other theories for the magnetization reversal     

Hard magnetic phase in rapidly quenched Zr-Co-B alloys

In order to identify a hard magnetic phase in rapidly quenched Zr-Co-B alloys and clarify its magnetic properties, Zr-Co-B ribbons, Zr-Co ribbons, and Zr-Co ingots were studied. The hard magnetic phase is interpreted as a Zr₂Co₁₁ intermetallic compound. This compound has a Curie temperature of 500°C and uniaxial magnetic anisotropy with an anisotropy field of 34 kOe. The magnetization of this compound was estimated to be 67 emu/g at 15 kOe. In addition to the hard magnetic phase, the low and high T_c phases appear in both binary and ternary alloys. The low T_c phase is FCC Zr₆Co₂₃ with T_c=180°C. The magnetization of Zr₆Co₂₃ was estimated to be 44 emu/g at 15 kOe. The high T_c phase is cobalt including a small amount of zirconium. In Zr-Co-B alloys, suitable boron addition is shown to enhance the coercive force. On the other hand, the addition increases the magnetization. While the boron addition produces cobalt, it reduces Zr₆Co₂₃ or quenches its ferromagnetism     

Sintered Sm2(Co, Fe,Cu,Zr)17 magnets withlight rare earth substitutions

The effects of partial substitution of light rare earths for Sm in (Sm_1-xR_x)₂ (Co,Fe,Cu,Zr)₁₇ have been investigated where R=Ce, Pr, Nd, Pr_0.5Nd _0.5, Ce_0.2Pr_0.4Nd_0.4 and x=0-0.5. Experiments show that both remanence and maximum energy product are improved for x=0.1-0.2, depending upon compositions and heat treatments. For a composition Sm_0.8R_0.2(Co_0.633Fe_0.286 Cu_0.061Zr_0.020)_7.59 with R =Ce_0.2Pr_0.4Nd_0.4, the authors obtained B_r=11.57 kG, _MH_c =15.5 kOe, _BH_c=10.33 kOe, H_k=10.03 kOe, and (BH)_max=30 MGOe     

Properties of the W-type hexaferritePbZn2Fe16O27

W-type Pb-hexaferrites were prepared by standard ceramic methods. The lattice constants found by refinement were a=0.59140±0.00006 nm and c=3.29209±0.00041 nm. The X-ray density of a typical composition PbZn_1.9Fe_15.3O_25.8 was ρ=5.32 g/cm³ and the Vickers microhardness value h _v=6 kN/mm². A plot of the saturation magnetization versus temperature is given. The extrapolated value of the saturation magnetization (H→∞, T→0) was σ_s=108 emu×g^-1, and the Curie temperature was T_c=600±20 K     

Effect of stress on the law of approach to saturation magnetizationin carbon steels

In high fields where the magnetization is approaching saturation, the resolved magnetic polarization I can be expressed by a power series of the inverse of external field H as: I=I_s-b/H ²-c/H³ . . ., or alternatively in terms of the reversible permeability μ_rev=1+(2b/H³+3c/H⁴+ . . .)/μ₀ where I_s is the spontaneous magnetic polarization and b, c, are constants. These equations express the law of approach to saturation magnetization. The coefficient b for a cubic crystal has been deduced as b=0.0762/I_s[K+1.5(λ₁₀₀-λ ₁₁₁)σ]², where σ is the applied stress and others are magnetic constants. The values of reversible permeability μ_rev under biasing field H were measured for carbon steels with applied stresses. The results showed that the square root of 2b changed linearly with the applied stress, The values of magnetic constant K andλ₁₀₀ -λ₁₁₁ were calculated, They agreed with the standard values, but were affected by chemical composition and heat treatment of materials, especially in λ₁₀₀-λ₁₁₁     

Al（OH）3和Cl一对稀土铝热浸镀层腐蚀行为的影响

以自制热浸镀稀土铝为研究对象,采用失重法、极化曲线、SEM和电化学阻抗测试研究了淡水中存在的A1（OH）3对镀层腐蚀行为的影响;同时,通过极化曲线考察了饱和A1（oH）3溶液中C1一浓度对镀层腐蚀的影响。结果表明：A1（OH）3能够抑制镀层破损钝化膜的修复,促进阳极活化,诱导镀层点蚀反应的发生,使腐蚀加剧;随Cl一浓度...     

Analysis of temperature-dependent magnetization in Sm-Fe-Ccompounds using a two-sublattice model

The temperature dependence of magnetization in Sm₃Fe ₂₀C_x (x =0.3, 0.6, 0.8) and Sm₂Fe_16.5C_1.0 intermetallic compounds with rhombohedral structure has been analyzed using molecular field theory. On the basis of a two-sublattice model, the molecular field coefficients are calculated using a numerical fitting method. The Curie temperature and the Fe-Fe, Sm-Fe, Sm-Sm magnetic interaction energies for the compounds are determined from these coefficients. The results show that the increase of the Curie temperature (T_c) with the increase of carbon content x is attributed mainly to the enhancement of the Fe-Fe exchange interaction energy caused by carbon atoms added     

Corrosion of tin in citric acid solution and the effect of some inorganic anions

The corrosion behaviour of tin in different concentrations of citric acid solutions (0.3–1.0 M, pH=1.8) was studied at 30 °C by potentiodynamic technique. The E/I profiles exhibit an active passive behaviour. The active dissolution involves one anodic peak A associated with a dissolution of the metals as Sn(II) species. The passivity is due to the formation of thin film of SnO₂ and or Sn(OH)₄ on the anode surface. The cathodic sweep shows a small peak C related to the reduction of the passive film. The peak current density I_p of peak A increases with increasing both acid concentration and sweep rate.

The effects of adding increasing concentrations of Na₂CrO₄, NaMoO₄, NaNO₃ and NaNO₂ on the corrosion of tin in 0.5 M citric acid at 30 °C were investigated. Both CrO₄²⁻ and MoO₄²⁻ ions inhibit the corrosion of tin and the extent of inhibition enhances with their concentrations. Addition of either NO₃⁻ or NO₂⁻ accelerates the corrosion of tin. NO₃⁻ ions are more aggressive than NO₂⁻ ions.     

Analytical electron microscopy of Sm(Co,Fe,Cu, Zr)9

Electron microscopic studies of as-cast Sm(Co,Fe,Cu,Zr)₉ magnets revealed a hexagonal phase of the type Sm₂(Co,Fe,Cu,Zr)₁₇ with crystal lattice parameters of a=0.84 nm and c=3.2 nm. After a solid solution treatment, only rhombohedral (3R) and hexagonal (2H) grains were found. After an additional annealing treatment at 800°C, grains with a microcellular precipitation structure similar to the one found in Sm(Co,Fe,Cu,Zr)_7.5 magnets occurred. In addition, in the as-cast and after-aged samples, other, partly unidentified Cu- or (Co,Fe)-enriched phases were detected     

NiTi substituted hexaferrites for magnetic recording

In order to obtain hexagonal ferrites with improved characteristics for application in the field of the magnetic recording, the ferrimagnetic Sr(NiTi)_x Fe_12-2xO₁₉ system is studied. Preliminary investigations suggested that NI is more effective than Co in reducing the magnetic anisotropy of hexaferrites. The system was analyzed as a function of the degree of substitution x and of the reaction temperature T_R and time τ. The reactivity of the mixtures and their magnetic characteristics (σ, H_c, H_A, T_c) were measured, and from the _χT(H) data it was possible to distinguish between single-domain or polydomain particles. The results are presented. The influence of the extraneous magnetic phases on the coercive field value was also studied and a preliminary investigation of the relation between coercive and anisotropy fields was carried out     

Annealing behavior of magnetic anisotropy in CoNbZr films

The effect of magnetic and nonmagnetic annealing on the magnetic anisotropy in CoNbZr films, formed by a DC opposing-targets sputtering method, was investigated. It was revealed that the origin of the magnetic anisotropy is the directional ordering of the magnetic atoms. The anisotropy fields and the direction of the easy axis obtained when the films are annealed in zero magnetic field are almost the same as those for the magnetic field parallel to the easy axis of the as-deposited films. When the films are annealed in a magnetic field perpendicular to the easy axis, the anisotropy field induced in parallel with the magnetic field, H_k(t), is well represented by the following formula: ln {1-H_k(t )/H_k(∞)∝-√Tt, where H_k(∞) is the thermal equilibrium value of the anisotropy field and D is the diffusion constant. The activation energy of the as-deposited film is 0.86 eV. Annealing the film increases the activation energy which is 2.1 eV when the film is annealed at a temperature of 450°C for 2 h     

Hexagonal ferrite particles for perpendicular recording prepared byion exchange

Particles of nonstoichiometric M-type barium hexaferrite with the chemical formula BaFe_10.5M_0.25O_17.05 (M=Mg, Cd, Co, Ni, Nd Zn) have been prepared by ion exchange in Ba containing molten salts from precursor ferrites with the β- or β"-alumina structure. The particles possess a plateletlike shape with diameters as low as 0.2 μm and as diameter-to-thickness ratio between 5 and 10. The Curie temperature is close to 470°C. Saturation magnetization values σ_s up to 64 emu g and coercive fields jH_c ranging from 0.5 to 1.5 kOe were found     

Characterization of fluorine-doped silicon dioxide film by Raman spectroscopy

We have measured Raman spectra of fluorine-doped SiO₂ (SiOF) films and quartz glass. From a comparison between Raman spectra of the SiO₂ film and quartz glass, it has been found that the SiO₂ film is under compressive stress and that it has more threefold ring defects than quartz glass. Raman bands from threefold and fourfold ring defects in SiOF films become week as the fluorine/oxygen (F/O) ratio increases and as the stress decreases. The decrease of intensities of these Raman bands shows that ring defects in SiOF films decrease as the F/O ratio increases and as the stress decreases. The triply degenerated ω₄ mode at 460 cm⁻¹ becomes sharp as the F/O ratio increases and as the stress decreases. Furthermore, the peak-frequency of ω₁ mode around 820 cm⁻¹ decreases with a decrease of stresses whereas that of ω₃ mode around 1065 cm⁻¹ increases. These results can be well understood in terms of a decrease of O-Si-O bonding angle caused by relaxation of stresses.     

Development of a microprocessor-based four probe DC resistivitysetup for Tc measurement of superconductingmaterials

The design of a microprocessor-based resistivity measurement system for high transition temperature (T_c) superconducting materials is described. This design includes interfacing an Intel 8085 microprocessor system with an IBM-compatible personal computer (PC) through RS-232C serial communication. This design is used to measure resistivity for superconducting samples of YBa₂Cu ₃O_7-x and strontium/potassium substituted YBa₂Cu₃O_7-x. A correction method is described for the parameters whose values are changing throughout the measurement period to minimize the measurement errors     

Lateral magnetic inhomogeneities in Co-Cr layers detected by FMR

Co-Cr layers deposited on Ge underlayers were investigated with ferromagnetic resonance (FMR). The thickness of the Co-Cr layers and the substrate temperature (T_s) during deposition were varied. Measurements with a vibrating sample magnetometer showed that an increase of T_s results in an increase of both the bulk saturation magnetization M_s and the perpendicular coercivity H_c^⊥. The FMR spectra, obtained with the applied field perpendicular to the sample, showed two resonances for all layers. The effective anisotropy field is positive for both resonances. The difference in effective anisotropy field does not change with thickness of the layer, but increases with increasing T_s. From this it is clear that the two resonances are not due to magnetic inhomogeneities in the growth direction, but must be due to lateral magnetic inhomogeneities. Inhomogeneities in composition, resulting in different values of M _s, or in geometric structure, resulting in different values of the demagnetizing factor N_d, are the most probable causes of the observed effects     

Magnetic properties of melt spun NdFe10Cr2-Nd0.67B0.33 pseudobinary alloys

The coercivity of the melt-spun pseudobinary (NdFe₁₀Cr ₂)_1-x (Nd₂B)_x alloys, in which Nd₂B represents a composition of Nd_0.67B_0.33, was systematically studied. It was found that significant coercivities are possible with optimal additions of the Nd-B composition at x=0.5-0.7. The as-spun (substrate velocity=10 m/s) coercivity increased from 0.1 kOe at x=0.0 to maxima of 7.0 and 7.5 kOe at x=0.5 and 0.7, due to the Nd₂ Fe₁₄B and a new Fe-Nd phase, respectively, as evidenced from thermomagnetic analysis and X-ray diffraction. Annealing the overquenched amorphous x=0.7 alloy led to the crystallization of the Nd₂Fe₁₄B phase, and a coercivity of 8.5 kOe was obtained     

Magnetic properties of Sm2Fe17Nxpowder and bonded magnet

Sm₂Fe₁₇N_x powders were prepared through metallurgical processes such as melting, casting, pulverizing, and gas nitrogenation. Epoxy resin and zinc-bonded magnets were prepared from the powder by a compression molding process. The magnetic properties of magnetically aligned Sm₂Fe₁₇N_x powder were (BH)_max=170 kJ/m³ (21.4 MG-Oe), Br=1.20 T, and H_cJ=547 kA/m (6.87 kOe). Those of an epoxy-bonded magnet were (BH)_max =103 kJ/m³ (13.0 MG-Oe) and Br=0.835 T. H _cJ values in excess of 2 MA/m (25 kOe) were observed in the case of a zinc-bonded magnet     

STM control of noninteger residual charge Q0 onthe central electrode of a double-tunnel junction

In a voltage-biased mesoscopic double-tunnel junction, the Coulomb threshold V_C is an e-periodic function of Q ₀, the charge on the inner electrode. In the STM work described here, a large Au tip images 100-Å Ag particles deposited on a cleaved BSCCO crystal substrate. Stable double junctions between the tip, the imaged particle, and the substrate are identified by Coulomb staircase I(V)'s. The control of Q ₀ is demonstrated by the variation of tip-particle spacing. The parameterization of such results permits a discussion of Q ₀ variation mechanisms