A study of magnetic properties of compacted amorphous powder cores

Magnetic properties of compacted cores which are formed from amorphous alloy powders prepared by a rapid quenching water atomization process are studied. The coercivity of the as-compacted core was estimated to beH _c=0.028(/I _s)+1200 with the idea that the coercive force depends on the magnitude of the stress variation. The a.c. magnetic properties are remarkably improved by use of the coupling agent and zinc stearate. The use of the amorphous powder core for choke coils of switching power supplies leads to the decrease of cut-off current, that is, an improvement in the efficiency of power supplies.     

Factors affecting the magnetic properties of consolidated amorphous powder cores

It has been shown that it is possible to produce high density amorphous metal compacts on a routine basis, that have interesting soft magnetic properties. A study of some of the parameters determining their magnetic properties has been made. As expected, interparticle insulation and compact thickness affect the a.c. properties. Surprisingly, the magnetic properties were found to be relatively independent of compact density, in the range 73 to 98% of theoretical density. Low or zero magnetostriction alloys gave superior properties. If more than ~ 10% interparticle insulation is employed then the alloy composition is of less consequence. It is shown that a wide range of properties may be obtained.     

The core-shell structured Fe-based amorphous magnetic powder cores with excellent magnetic properties

The Fe-based soft magnetic amorphous powder cores (AMPCs) with excellent comprehensive magnetic properties were successfully designed and fabricated using the core-shell structured FeSiBCCr/TiO₂ composite powders. The influence of the concentration of water (H₂O) for the magnetic performance of the AMPCs has been systematically studied based on careful analysis of the process of nucleation and growth of TiO₂ under different H₂O concentration in the reaction system. The growth process for the TiO₂ coating layer with the H₂O concentration in the range of 0.01–0.02 ml/g corresponds to the heterogeneous nucleation phase, while the mixing phase of heterogeneous and homogeneous nucleation occurs when the concentration of H₂O increases to 0.03 ml/g. Optimized soft magnetic properties have been achieved for the AMPCs with H₂O concentration of 0.02 ml/g, including high permeability of 81.5 with a high frequency stability up to 10 MHz, high quality factor of 102 at 530 kHz, low core loss of 42 mW/cm³ at 500 kHz for B_m = 0.01 T, and better DC-bias property of 52% at a bias field of 100 Oe due to the uniform and proper thickness insulation coating layer, which can be used to produce miniature magnetic components for applications in medium and high-frequency fields.     

The effect of ribbon curvature on the magnetic properties of Fe-based amorphous cores

Coercivity and losses properties of Fe₈₀Si₉B₁₁ (at.%) amorphous cores with different radius of curvature have been studied. It shows that coercivity and core loss of the Fe₈₀Si₉B₁₁ amorphous alloy increases with the decrement of the winding radius. The domain structure of the ribbons is different for different radius of curvature R. The domain width increases with the decrease of the radius of curvature, since the stress within the ribbon with lower radius of curvature is much stronger. Magnetic-elastic anisotropy energy has also been studied.     

纳米晶软磁复合磁粉芯在中高频段性能研究

介绍了利用球磨后的FeCuNbSiB合金粉末冷压制作纳米晶复合磁粉芯的工艺.探讨了粉末粒度为80～200目,绝缘剂量为1%～8%时纳米晶复合磁粉芯的频率特性,直流叠加特性及品质因数Q.制备出的平均粒度为80目的磁粉芯有效磁导率μe在1MHz范围内恒为85,在100kHz时其峰值Q为65,在f=50kHz,Bm=50mT测试条件下其损耗为102mW/cm3.其功率损耗比传统铁粉芯,Fe-Ni粉芯小.     

Enhanced high frequency properties of FeSiBPC amorphous soft magnetic powder cores with novel insulating layer

Fe-based amorphous magnetic powder cores (AMPCs) with excellent comprehensive properties were successfully fabricated via using the uniform double insulating layer core-shell structured FeSiBPC/Fe₃O₄@Epoxy resin (EP). The effects of the in-situ hydrothermal oxidized time on the magnetic properties of the AMPCs have been systematically investigated on the basis of the growth mechanism of the insulating layer of spherical amorphous powder in alkaline environment. The hydrothermal oxidation process could well ensure the uniformity of the oxide layer composed of Fe₃O₄ nanoparticle. The evolution of the insulating layer is a process of homogeneous nucleation and growth at different hydrothermal oxidation time. After 10 h of hydrothermal oxidation, a thin and dense layer composed of Fe₃O₄ nanoparticle was formed on the surface of the amorphous powder. As a consequent, the FeSiBPC AMPCs exhibit excellent performance such as stable effective permeability of 49.5 at 2 MHz, a very low core loss of 187 mW/cm³ at 100 kHz@0.05 T and high-quality factor of 160 at 600 kHz. The results indicate that the thickness of the Fe₃O₄ insulating layer can be completely controlled via the reaction parameters, and can effectively suppress the eddy current loss, which is promising for high-frequency electromagnetic systems.     

Instabilities in crystallization and magnetic behavior of Fe-Si-B amorphous alloys

Experimental evidence is presented to support the idea that the boron content, which influences the Fe-Fe pair distances and the electronic structure, determines the magnetic properties of amorphous Fe-Si-B alloys. Magnetic moment variations are ascribed to the local environment of the iron atoms and to the electronic structure of the amorphous Fe-Si-B alloys while the T_c changes are due to the increase of the Fe-Fe pair distances. The mean atomic magnetic moments per iron atoms were extrapolated at 0 K. Radial Distribution Analysis combined with Rietveld refinement achieved an estimation of Fe-Fe distances in amorphous and partially crystallized specimens, while the peculiarities in crystallization were revealed by HRTEM.     

Effect of hydrogen on the magnetic behavior of CoFeCrSiB amorphous alloys

Alloying with Fe caused a non-monotonic change in the soft magnetic properties of Co_71−X Fe _X Cr₇Si₈B₁₄ alloys. Hydrogenation caused a progressive deterioration in the soft magnetic properties. The differences in the response of the alloys is possibly due to a non-systematic variation in the inter-atomic exchange interactions which modulates the dipole moment, and due to introduction of internal stresses on hydrogen charging.     

New extensometers using amorphous magnetostrictive ribbon wound cores

New reliable and accurate extensometers are presented using a single amorphous core multivibrator with a dc output. These extensometers can detect strains as large as 40 percent for tensile test samples without any destruction due to the outstanding elasticity of the Metglas 2605A amorphous ribbon-wound cores. High linearity (0.18 percent full scale (FS)) is realized by annealing and applying 1000 times alternating stresses to the cote. Hysteresis against alternating strains is removed to less than 0.48 percent FS by the effect of a compensation spring. The amorphous core extensometer has advantageous points regarding reliability, temperature stability, and maximum operating temperature over conventional extensometers using semiconductor strain gauges.     

Core loss in amorphous cut cores with air gaps

The effects of air gaps on the high-frequency core loss in cut cores made of amorphous ribbons are discussed and methods to reduce the core loss in them are proposed. It has been found that the high-frequency core loss in amorphous cut cores with air gaps increases strikingly with increasing air-gap length. The increase in the core loss due to air gaps is remarkable in high-frequency and low-induction range. Measurement of leakage magnetic flux as well as analysis of the flux distribution and the eddy current in an amorphous core with the finite-element method suggests that the increase in the core loss due to air gaps observed in the amorphous cores can be attributed to the in-plane eddy current loss generated by the leakage flux perpendicular to ribbon surfaces. Suppression of the leakage flux normal to ribbon surfaces by using semicircular cores and reduction in width of ribbons of which cores are made decreases the high-frequency core loss in amorphous cut cores with air gaps     

Co对Nd-Fe-Al大块非晶合金的晶化行为和磁性能的影响

采用示差扫描量热法(DSC)，X射线衍射(XRD)和振动样品磁强计(VSM)研究了Co对Nd—Fe-Al大块非晶合金的非晶形成能力，晶化行为和磁性能的影响。结果表明：加入Co元素后可以显著提高Nd—Fe-Al大块非晶合金的非晶形成能力以及提高合金的居里温度。Nd60Fe30-xAl10Cox(z=0、5、10)大块非晶合金在室温有较高的内禀矫顽力，具有硬磁性。内禀矫顽力随着Co含量的增加变化不大．但是饱和磁化强度和剩磁则随着Co含量的增加有所下降。Nd60Fe3-xAl10Cox(x=0、5、10)大块非晶合金具有的硬磁性能来自于非晶相。合金少量晶化后，磁性能变化不大。完全晶化后合金的硬磁性迅速消失。     

Self-assembled virus-like particles with magnetic cores

Efficient encapsulation of functionalized spherical nanoparticles by viral protein cages was found to occur even if the nanoparticle is larger than the inner cavity of the native capsid. This result raises the intriguing possibility of reprogramming the self-assembly of viral structural proteins. The iron oxide nanotemplates used in this work are superparamagnetic, with a blocking temperature of about 250 K, making these virus-like particles interesting for applications such as magnetic resonance imaging and biomagnetic materials. Another novel feature of the virus-like particle assembly described in this work is the use of an anionic lipid micelle coat instead of a molecular layer covalently bound to the inorganic nanotemplate. Differences between the two functionalization strategies are discussed.     

Testing the characteristics of magnetic amplifier cores

Conclusion In the design of self-saturating magnetic amplifiers one must abide by the characteristics based on the demagnetization curve B_y=f(H_y) and not by those based on symmetrical magnetization reversal.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 43–45, September 1972.     

Drying of materials in magnetic high-frequency field

A theoretical analysis is made of energy relations which determine the efficiency of drying granular materials in a magnetic high-frequency field.     

The magnetic properties of amorphous SmCo-films

The room temperature magnetic hysteresis properties of flash-evaporated Sm1-xCox-films (x=0.74, 0.82,0.89) with induced uniaxial in-plane anisotropy have been analyzed for their dependence on the substrate material (glass,Cu,Al) and the substrate temperature Tsubpresent during evaporation (100Ksub<1000K).     

Influence of magnetic annealing on high-frequency magnetic properties of FeCoNd films

FeCoNd thin film with thickness of 166 nm has been fabricated on silicon (1 1 1) substrates by magnetron co-sputtering and annealed for one hour under magnetic field at different temperatures (T_a) from 200 °C to 700 °C. The As-deposited and annealed FeCoNd film samples at T_a ≤ 500 °C were amorphous while the ones obtained at T_a ≥ 600 °C were crystallized. We found that the perpendicular anisotropy field gradually decreases as the annealing temperature increases from room temperature to 300 °C. A well induced in-plane uniaxial anisotropy is achieved at the annealing temperature between 400 and 600 °C. The variation of the dynamic magnetic properties of annealed FeCoNd films can be well explained by the Landau-Lifshitz equation with the variation of the anisotropy field re-distribution and the damping constant upon magnetic annealing. The magnetic annealing might be a powerful post treatment method for high frequency application of magnetic thin films.     

Thermoelectric behaviour of amorphous magnetic alloys

The Thermoelectric emfs of thermocouples formed by amorphous METGLAS 2826 (Fe₄₀Ni₄₀P₁₄B₆) and METGLAS 2826B (Fe₂₉Ni₄₉P₁₄B₆Si₂) with standard thermocouple wires like copper, chromel, alumel, etc., were measured as a function of temperature between −196° C and 30° C to assess their suitability as thermoelectric temperature sensors. Thermoelectric emfs generated by METGLAS 2826/Cu and METGLAS 2826B/Cu thermocouples at −196° C are about an order of magnitude smaller when compared to thermal emfs of a standard copper/constantan thermocouple at the same temperature.