Comparison of the soft magnetic properties of permalloy and conetic thin films

The soft magnetic properties of the substrate/[non-buffer or buffer Ta]/[permalloy (Ni₈₀Fe₂₀) or conetic (Ni₇₇Fe₁₄Cu₅Mo₄)]/Ta prepared by ion beam sputter deposition are investigated. The value of the surface resistance of the conetic film is twice as high as that of the permalloy film. The value of the coercivity and magnetic susceptibility of the conetic film decreased by 25% and doubled relative to that of the permalloy film. The coercivity, with a value of 0.12 Oe, and the magnetic susceptibility, with a value of 1.2×10⁴ for the conetic film, are suitable for soft magnetic biosensor applications.     

Magnetic properties of soft magnetic composites prepared with crystalline and amorphous powders

Physical properties of soft magnetic composites prepared with a mixture of amorphous (FeSiBC) and crystalline (Fe) powders coated with distinct electrical insulator contents are reported. Density, saturation polarization, permeability and coercivity of the cores reduce linearly with the increase of the softer magnetic phase amount and a general relation can be expressed by a rule of mixtures. The behavior of the coercivity, as a function of the magnetic phase content, differs from that previously reported for magnetic composites prepared with equal amounts of magnetic and non-magnetic phases. For frequencies upto 1 kHz the magnetic losses of the cores are constant, following the same behavior of the coercivity. A qualitative explanation of the behavior of the latter is addressed based on an expression applicable for crystalline and amorphous materials.     

High-frequency magnetic properties of soft magnetic cores based on nanocrystalline alloy powder prepared by thermal oxidation

FeSiBNbCu nanocrystalline alloy powder was thermally oxidized in an air atmosphere to enhance an oxide layer formation on the surface of the powder and subsequently toroidal shape FeSiBNbCu nanocrystalline alloy powder cores were prepared by compaction at room temperature. The phase change on the surface of FeSiBNbCu nanocrystalline alloy powder by thermal oxidation was analyzed and its effect on the high frequency magnetic properties of the compacted cores was investigated. By thermal oxidation, the formation of the oxide layer consisting of Fe₂O₃, CuO, and SiO₂ on the surface of FeSiBNbCu nanocrystalline alloy powder was enhanced and the thickness of oxide layer could be controlled by changing the thermal oxidation time. FeSiBNbCu nanocrystalline alloy powder core prepared from the powder treated by thermal oxidation exhibits a stable permeability up to high frequency range over 10 MHz. The core loss could be reduced remarkably and the dc-bias property could be improved significantly, which were due to the formation of oxide layer consisting of Fe₂O₃, CuO, and SiO₂ on the FeSiBNbCu nanocrystalline alloy powder. The improvement in high-frequency magnetic properties of the FeSiBNbCu nanocrystalline alloy powder cores could be attributed to the effective electrical insulation by oxide layer between the FeSiBNbCu nanocrystalline alloy powders.     

Effect of hot deformation on texture and magnetic properties of Sm-Co and Pr-Co alloys

Nanocrystalline PrCo₅, SmCo₅ and Sm₂(Co,Fe,Mn)₁₇ alloys were subjected to a high-degree plastic deformation at 950 °C with the height reduction ranging from 70% to 95%. With increasing degree of deformation, the PrCo₅ and SmCo₅ magnets showed improvement of the deformation-induced [0 0 1] texture. The PrCo₅ alloys, known to develop a superior texture at the lower degrees of deformation, showed only modest improvement and their magnetic performance was undermined by a low coercivity. The SmCo₅ alloys had their texture markedly enhanced and, after height reduction by 94.5%, they exhibited a remanence of 8.6 kG, maximum energy product of 18 MGOe and an intrinsic coercivity of 22.8 kOe. No induced texture was found in the alloys based on the Sm₂Co₁₇ structure. The microstructures of the hot-deformed alloys were studied with a transmission electron microscopy, and possible mechanisms of the texture development in the RCo₅ alloys (R=Pr, Sm) are briefly discussed.     

Synthesis of nanocrystalline Co-Ni alloys by precursor approach and studies on their magnetic properties

Nanocrystalline Co-Ni alloys with different compositions were prepared by polyol reduction of mixed cobalt nickel hydroxides. The precursors (mixed cobalt nickel hydroxides) were prepared by co-precipitation. Powder X-ray diffraction analysis indicated the formation of fcc phase in the alloys and their crystallite size in the range 17-25 nm. Scanning electron microscopy and transmission electron microscopy studies revealed the morphology of the particles as being close to spherical, and the energy dispersive X-ray analysis showed the stoichiometry of the alloys. The magnetization as a function of field and temperature of the alloys, measured using a superconducting quantum interference device, showed superparamagnetic behavior with negligible coercivity and remanence values.     

On the magnetic properties of mechanosynthesized Co-Fe-Ni ternary alloys

X-ray diffraction, Mössbauer spectroscopy and magnetization measurements were used as complementary methods to obtain structural data and to determine magnetic properties of the mechanically synthesized and subsequently thermally treated Co-Fe-Ni alloys. New, however approximate, phase diagrams were established on the basis of X-ray diffraction investigations. Mössbauer spectroscopy and magnetization measurements allowed to reveal practically linear correlation between the average values of the hyperfine magnetic field induction, 〈B_hf〉, and the effective magnetic moments, μ_eff, of the alloys. The decrease in 〈B_hf〉 with the number of electrons per atom, e/a, was observed. Moreover, the dependence of μ_eff on the valence 3d and 4s electrons per atom follows the Slater-Pauling curve. Thermal treatment of mechanosynthesized Co-Fe-Ni alloys led to some changes in the phase diagrams, increase in the grain size and decrease of the level of internal strains in alloys. Dependencies of lattice constants, average hyperfine magnetic fields, effective magnetic moments and Curie temperatures on the number of electrons per atom have the same trends for mechanically synthesized as well as for thermally treated alloys.     

Influence of structure on coercivity in nanocrystalline (Fe1−xCox)86Hf7B6Cu1 alloys

The relationship between coercivity and structure in nanocrystalline (Fe_1−xCo_x)₈₆Hf₇B₆Cu₁ (x=0–1) alloys was surveyed. It was found that the increase of Co content in the alloys studied was accompanied by the increase of coercivity. However, we suggest that the factors influencing the coercivity change with the concentration of cobalt in these nanocrystalline alloys. In the iron-rich alloys, the average grain size and magnetostriction play predominant roles in the coercivity. On the other hand, in the case of cobalt-rich alloys, the coercivity mostly originates from the FCC-Co phase with large magnetocrystalline anisotropy and the weak exchange coupling between BCC-Fe(Co) and FCC-Co(Fe).     

The correlations between processing parameters and magnetic properties of an iron–resin soft magnetic composite

In this study, internal microstrain of an iron–resin composite produced by powder metallurgy has been calculated using the Williamson–Hall method. The effects of microstrain evolution during different processing conditions on magnetic properties such as coercive force and hysteresis loss have been investigated. The results show that there are regular and similar changes of coercivity and hysteresis loss. Both of these properties are directly dependant on the pinning effect of the internal microstrain against the movement of magnetic domain walls during magnetization process.     

Magnetic properties of iron-based soft magnetic composites with MgO coating obtained by sol-gel method

Soft magnetic composites with a thin MgO insulating layer were produced by a sol-gel method. Energy dispersive X-ray spectroscopy, X-ray analysis, Fourier transform infrared spectroscopy, density measurement and compositional maps confirmed that thin layers of MgO covered the iron powders. Coercivity measurement showed that the stress relaxation and reduction of hysteresis loss efficiently occurred at 600 °C. At this temperature, the phosphate insulation of commercial SOMALOY^TM samples degrade and their electrical resistivity, magnetic permeability and operating frequency decreases noticeably. The results show that the MgO insulation has a greater heat resistance than conventional phosphate insulation, which enables stress-relief at higher temperatures (600 °C) without a large increase in eddy current loss. The results of annealing at 600 °C show that the electrical resistivity and ferromagnetic resonance frequency increased from 11 μΩ m and 1 kHz for SOMALOY^TM samples to 145 μΩ m and 100 kHz for the MgO insulated composites produced in this work.     

Composition dependence of microstructure,magnetic and microwave properties in ball-milled FeSiB nanocrystalline flakes

The soft magnetic nanocrystalline/amorphous FeSiB flakes were fabricated by the ball-milling method and evaluations were made of the composition, microstructure, magnetic and microwave properties in the milling process. An investigation of the relationship between microstructure and magnetic/microwave properties showed that the electromagnetic characteristics were attributed to the changes of nanograin size, crystal and amorphous content corresponding to the composition variation. The replacing of Fe atoms by Si in α-Fe crystal caused the decrease of grain size, saturation magnetization and coercivity, while B content devoted to amorphous phase and decreased the permittivity. Consequently, it was observed that the optimum composition for microwave performance is Fe₈₂Si₅B₁₃.     

The effect of magnetic field on the electrodeposition of CoFe alloys

The superimposition of a homogenous magnetic field during an electrodeposition of CoFe alloy was investigated. A magnetic field superimposed parallel to the electrode surface increases the limiting current density and the deposition rate due to the magnetohydrodynamic (MHD) effect. The deposits obtained in this field configuration appear smoother and more homogenous than the ones obtained without the magnetic field. On the contrary, a magnetic field superimposed perpendicular to the electrode surface does not influence significantly the electrochemical reaction but the morphology of the deposited layers is strongly affected. The roughness is strongly increased in this field configuration and grains grow as separated columns aligned perpendicular to the electrode surface, in the field direction. A magnetic field applied during the deposition affects the magnetic properties of the deposited layers as well. These changes are discussed with respect to the surface roughness and the internal stress state of the layer.     

Effect of warm compaction on the magnetic and electrical properties of Fe-based soft magnetic composites

This paper investigates the effect of warm compaction on the magnetic and electrical properties of Fe-based soft magnetic composites at operating frequencies between 0.1 and 10 kHz. The magnetic and electrical properties of samples were measured by an LCR meter and morphology of the samples was characterized by scanning electron microscopy. It was shown that the compacted sample prepared at 800 MPa and 550 °C had the lowest magnetic loss and electrical resistivity, and highest magnetic induction and effective permeability in comparison with other samples compacted at 800 MPa and room temperature, 150, 250, 350 and 450 °C.     

Improving permanent magnetic properties of rapidly solidified nanophase RE-TM-B alloys by compositional modification

Rapid solidification is one of the most important techniques to produce nanocrystalline rare-earth-transition metal-boron (RE-TM-B) hard magnetic materials. To achieve high performance on these NdFeB-based alloys, compositional modification and microstructure optimization have been frequently employed. In this short review, various substitutions and doping elements have been discussed regarding to their behaviors in adjusting the individual or combined hard magnetic properties as well as the microstructure based on our recent results. It has been demonstrated that Pr and Dy enhance coercivity _jH_C, whereas Sm reduces _jH_C due to their effects on intrinsic properties. Co improves the thermal stability as well as the microstructure. Introducing Fe₆₅Co₃₅ is a possible approach to enhance the magnetization and maximum energy product (BH)_max. As a doping element, Ta was found to play an important role to obtain an appropriate combination of magnetic properties for this type of alloys.     

Microstructure and soft magnetic properties of Finemet-type ribbons obtained by twin-roller melt-spinning

Soft magnetic ribbons of Finemet-type (Fe_73.5Cu₁Nb₃Si_13.5B₉) alloys are synthesized by the twin-roller melt-spinning technique directly from the melt, at tangential wheel speeds of 15, 18, 19 and 20 m/s. The microstructure and the magnetic properties are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA) and hysteresis loops measurements. Samples cooled at 20 m/s are amorphous, while those quenched at lower wheel speeds are partially crystalline. All samples studied present saturation magnetization values (150-160 A m²/kg) higher than the commercial Finemet alloys (∼135 A m²/kg), obtained by controlled crystallization of amorphous single-roller melt-spun alloys. Optimal soft magnetic properties - σ_S=(154±8) A m²/kg and H_C=(6.9±0.9) A/m - are found in samples quenched at 19 m/s, consisting of size-distributed bcc Fe-Si nanograins (∼18 nm in average) embedded in an amorphous residual matrix. A minority nanocrystalline magnetic phase (≤10 nm) is also detected.     

A novel method determining longitudinally induced magnetic anisotropy in amorphous and nanocrystalline soft materials

In ferromagnetic amorphous and nanocrystalline soft magnetic alloys the induced magnetic anisotropy plays a fundamental role in the hysteresis behavior but, due to the elongated shape, it can be measured only if K_U is perpendicular to the sample long axis. In order to measure the longitudinal induced anisotropy, an original method derived from known thin layers measurement techniques was used. Hysteresis loops shifted by perpendicular bias field were recorded for this purpose. Direct measurement of the longitudinal induced anisotropy in amorphous and nanocrystalline ribbons or wire without needing sample preparation is reported for the first time. Evidence of self-induced anisotropy is brought in a Fe–Co-based nanocrystalline alloy.     

Annealing temperature effect on microstructure,magnetic and microwave properties of Fe-based amorphous alloy powders

Fe₇₄Ni₃Si₁₃Cr₆W₄ amorphous alloy powders were annealed at different temperature (T) for 1.5 h to fabricate the corresponding amorphous and nanocrystalline powders. The influences of T on the crystalline structure, morphology, magnetic and microwave electromagnetic properties of the resultant samples were investigated via X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and vector network analyzer. The results show that the powder samples obtained at T of 650 °C or more are composed of lots of ultra-fine α-Fe(Si) grains embedded in an amorphous matrix. When T increases from 350 to 750 °C, the saturated magnetization and coercivity of the as-annealed powder samples both increase monotonously whereas the relative real permittivity shows a minimal value and the relative real permeability shows a maximal value at T of 650 °C. Thus the powder samples annealed at 650 °C show optimal reflection loss under −10 dB in the whole C-band. These results here suggest that the annealing heat treatment of Fe-based amorphous alloy is an effective approach to fabricate high performance microwave absorber with reasonable permittivity and large permeability simultaneously via adjusting T.     

The practical limits for enhancing magnetic property combinations for bulk nanocrystalline NdFeB alloys through Pr,Co and Dy substitutions

Pr, Co and Dy additions have been employed to improve the combinations of magnetic properties for nanocrystalline Nd_xFe_94−xB₆ melt spun alloys. The dependences of the magnetic properties on the solute element concentrations have been extensively investigated and the relationships between the measured remanence, maximum energy product (BH)_max and intrinsic coercivity for several compositional series are discussed. The composition ranges for these elemental substitutions which can be used to achieve the highest values of (BH)_max are identified. It is found that, when we employ individual or combined substitutions of Pr and Dy for Nd and Co for Fe in NdFeB alloys with various RE:Fe ratios, the practical limit of (BH)_max lies in the range ∼160–180 kJ/m³, combined with a coercivity in the range ∼400–800 kA/m.     

Studies of magnetic properties of permalloy (Fe-30%Ni) prepared by SLM technology

In the present study, a high permeability induction Fe-30%Ni alloy cubic bulk was prepared by the selective laser melting process. In order to reveal the microstructure effect on soft magnetic properties, the microstructure and magnetic properties of the Fe-30%Ni alloy were carefully investigated by scanning electron microscopy, X-ray diffraction and hysteresis measurements. The bcc-Fe (Ni) phase formation is identified by X-ray diffraction. Meanwhile, it was found that low bcc lattice parameter and high grain size could be obtained when high laser scanning velocity and low laser power were used. Moreover, the lowest value of coercivity is 88 A/m, and the highest value of saturation magnetization is 565 Am²/kg, which can be obtained at a low laser scanning velocity of 0.4 m/s and high laser power input at 110 W.     

Sputtering gases and pressure effects on the microstructure,magnetic properties and recording performance of TbFeCo films

The MsHc value is considered to be a key factor in high-density recording, and controlling the microstructure on the magnetic underlayer was found to be an effective way of increasing the MsHc of the amorphous TbFeCo magneto-optical (MO) medium. In this paper, we investigate the TbFeCo film's magnetic properties and the effects on the microcolumnar structure, which depends on the sputtering conditions of using various sputtering gases including Ar, Kr, and Xe, and the recording characteristics of TbFeCo memory layers. With heavy sputtering gases such as Kr or Xe, the columnar structure can be prepared in a TbFeCo film at a pressure lower than 1.0 Pa. The columnar structure of a recording layer can be effectively formed thanks to the effects of the magnetic underlayer, which has a fine surface even in the sputtering process in which Xe gas is used. The above applies to the sputtering process in which Ar gas is used. Also, when Xe gas is used in the sputtering process, coercivity Hc is increased through the formation of a well-segregated microcolumnar structure built on domain wall pinning sites, and we obtain a large MsHc and a high squareness ratio of the Kerr-hysteresis loop. Our results indicate that processing a TbFeCo film with heavy sputtering gases is suitable for tiny mark stability because the temperature gradient of Hc is increased. The objective of the low-pressure sputtering process using Xe gas to produce the columnar structure is to achieve ultra-high-density recording with tiny mark stability in the TbFeCo medium. This has been confirmed with magnetic force microscope (MFM) images of stable tiny marks recorded on TbFeCo film.     

Structural, electronic and magnetic properties of the Mnben Ni(110) c(2×2) surface alloy

Using first-principles total energy method, we study the structural, the electronic and the magnetic properties of the MnNi(110) c(2×2) surface alloy. Paramagnetic, ferromagnetic, and antiferromagnetic surfaces in the top layer and the second layer are considered. It turns out that the substitutional alloy in the outermost layer with ferromagnetic surface is the most stable in all cases. The buckling of the Mn–Ni(110) c(2×2) surface alloy in the top layer is as large as 0.26á(1á=0.1 n13) and the weak rippling is 0.038 AA in the third layer, in excellent agreement with experimental results. It is proved that the magnetism of Mn can stabilize this surface alloy. Electronic structures show a large magnetic splitting for the Mn atom, which is slightly higher than that of Mn–Ni(100) c(2×2) surface alloy (3.41 eV) due to the higher magnetic moment. A large magnetic moment for the Mn atom is predicted to be 3.81 μ_B. We suggest the ferromagnetic order of the Mn moments and the ferromagnetic coupling to the Ni substrate, which confirms the experimental results. The magnetism of Mn is identified as the driving force of the large buckling and the work-function change. The comparison with the other magnetic surface alloys is also presented and some trends are predicted.