High Coercive Force Research Articles

Magnetic properties of Fe–∼30 at% Pd films

Fe–Pd alloys with about 30 at% of Pd belong to the group of alloys exhibiting a thermoelastic martensitic transformation. The magnetic properties of the Fe–∼30 at% Pd thin films with the disordered FCC structure were examined. A relatively high coercive force of the films was measured. In one of the film samples, a case of out-of-plane magnetization occurred.

Magnetic properties in some sputtered RCo 2 amorphous alloys (R = rare-earth = Er, Sm, Tb)

The magnetic properties have been investigated in some RCo 2 amorphous alloys presenting highly anisotropic magnetic systems. The magnetization process, at different temperatures, have been studied over a wide magnetic field range (up to 10 T) and temperature range (10–300 K) using a vibrating sample magnetometer (VSM). Samples with various compositions have been annealed at different temperatures. The most important results are: (1) heat treatment and composition affect the shape of hysteresis loops with high coercive forces, large high field susceptibility even up to high magnetic field confirming the sperimagnetic structure, (2) Rayleigh laws have been validated, when it is possible, for both amorphous and nanocrystallised samples but a deviation is observed in the very weak fields. This deviation can be explained by the importance of magnetostatic effects and magnetostriction.

Structure phase transition and magnetic properties of nanocrystalline Zn0.6CoxFe2.4－xO4

A series of nanocrystalline powders Zn06CoxFe24-xO4 ( x=0—030) was synthesized by the solgel technique. The structure and mag netic properties was investiga ted and analyzed through the xray diffraction (XRD) patterns and the vibrating sample magnetometer (VSM). The experimental results show that αFe2O3 tra nsitio nal phase appears in the temperature range from 550℃ to 800℃. Single-phase zinc-cobalt ferrites with a spinel structure are obtained when the temperature is beyond 800℃. With relatively higher values of the cobalt content x=0075 — 015, the specific saturation magnetization climbs up at first and then falls d o wn with the increase of the cobalt content. The coercive force strength Hc of Zn06CoxFe24-xO4 reaches its highest value 47520A/m when x=0075 at 1300℃. Hc increas es slowly with temperature near 1200℃ when x≥015 and remains in a flat s tate at 1200—1300℃ and moderate increase is obtained by increasing the x value. High specific saturation magnetization and coercive force can be obtained simultaneo usly when the cobalt content is near 010

Enhanced coercive-force of Al-substituted Bi-GdIG nanoparticles with magnetic compensation composition

In garnet particles, higher coercive-force is required to develop a practical magneto-optical storage media. Therefore we in this article develop high coercive-force particles reflecting the magnetic compensation induced by the aluminum substitution for applying the garnet particles to magneto-optical storage media. Nanoparticles of aluminum substituted bismuth gadolinium iron garnet (Bi-GdAlIG) exhibit a magnetic compensation at room temperature. The Bi-GdAlIG nanoparticles were made using coprecipitation and heat-treatment processes. The magnetic profiles of the Bi-GdAlIG (BiGd/sub 2/Al/sub x/Fe/sub 5-x/O/sub 12/; 0 /spl les/ x /spl les/ 1.2) nanoparticles shows shallow minima at x=0.7 reflecting the magnetic compensation induced by the aluminum substitution. The coercive-force also peaks at x=0.7, which can be consistently explained by the magnetic compensation. The BiGd/sub 2/Al/sub 0.7/Fe/sub 4.3/O/sub 12/ nanoparticles demonstrate the enhanced coercivity of 320 Oe, which is factor of 2 larger than the x=0. The average size of the BiGd/sub 2/Al/sub 0.5/Fe/sub 4.5/O/sub 12/ nanoparticles was estimated 55 nm by Scherrer's equation, and observed to be about 100 nm by scanning electron microscope image.

Magnetic and conductive Fe 3O 4–polyaniline nanoparticles with core–shell structure

Magnetic and conducting Fe 3O 4–polyaniline (PANI) nanoparticles with core–shell structure have been prepared in the presence of Fe 3O 4 magnetic fluid in aqueous solution containing dodecylbenzene sulfonic acid sodium salt (NaDS) as a surfactant and dopant. The conductivity of the composites at room temperature depended on Fe 3O 4 content and doping degree. The magnetic properties of the resulting composites showed ferromagnetic behavior, such as high-saturated magnetization ( M s=4.22–48.4 emu/g) and high coercive force ( H c=8–55.3 Oe). The saturated magnetization increased with the increasing Fe 3O 4 content. A structural characterization by elemental analysis, Fourier transform infrared, transmission electron micrograph (TEM) and powder X-ray diffraction (XRD), proved that nanometer-sized Fe 3O 4 (20–30 nm) in the composites was attributed to the ferromagnetic behavior of the composites. The average size of Fe 3O 4–polyaniline nanoparticles with core–shell structure was about 80 nm, and polydisperse. The results of TG, IR and UV spectra indicated that Fe 3O 4 nanoparticles could improve the composite thermal stability possibly due to the interaction between Fe 3O 4 particles and polyaniline backbone.

Ba-ferrite 박막의 제조 및 자기적 특성에 관한 연구

Si 기판 위에 <TEX>$\alpha$</TEX>-Fe<TEX>$_2$</TEX>O<TEX>$_3$</TEX>을 하지층으로 하는 Ba-ferrite 박막을 pulsed laser deposition system으로 제조하여 결정학적 및 자기적 성질을 X선 회절, SEM, Mossbauer 분광법 및 VSM을 사용하여 연구하였다. <TEX>$\alpha$</TEX>-Fe<TEX>$_2$</TEX>O<TEX>$_3$</TEX>박막은 Si 기판위에 PLD를 이용하여 기판온도 400 <TEX>$^{\circ}C$</TEX>, 산소압력 0.1 Torr로 5분간 증착 하였고 그 위에 두께를 달리하여 Ba-ferrite 박막을 제조하였다. Ba-ferrite 결정은 가늘고 긴 모양의 결정립들로 형성되었으며 두께에 따라 그 모양과 상태가 변화하였다. Mossbauer 분광법으로부터 Ba-ferrite 결정내의 Fe 원자의 스핀 방향은 두께가 얇을수록 하지층의 영향으로 기판에 수직으로 정렬하려는 경향을 보이고 있음을 확인하였다. 자기이력곡선의 각형비 역시 두께가 얇을수록 더 크며 이러한 특성은 수평에 비하여 수직의 경우가 더 강하게 나타났다. 보자력 역시 같은 경향을 보이나 포화자화의 값은 수평의 경우에 더 큰 값을 나타내었다. 결정구조는 Magnetoplumbite로서 두께가 작아질수록 결정상수 <TEX>$\alpha$</TEX>는 감소하고 c는 증가하는 경향을 보였다. Ba-ferrite thin films were prepared on Si substrate with <TEX>${\alpha}$</TEX>-Fe<TEX>$_2$</TEX>O<TEX>$_3$</TEX> underlayer by a pulsed laser deposition system and characterized by X-ray, SEM, Mossbauer spectroscopy and VSM. The appropriate conditions of pulsation in <TEX>${\alpha}$</TEX>-Fe<TEX>$_2$</TEX>O<TEX>$_3$</TEX> and Ba-ferrite were the oxygen pressure of 0.1 Torr at a substrate temperature of 400<TEX>$^{\circ}C$</TEX>. Ba-ferrite crystals had the forms of ellipsoidal or needle and the grains shaped the more lumps with increasing the film thickness. Mossbauer spectroscopy assured that the direction of atomic spin in Fe ion was not random but had the tendency of arrangement normal to the substrate. The coercive force and squareness of hysteresis were larger in normal than in plane to the substrate but, the magnetic saturation moment was contrary to them. The spin arrangement was strongly affected by <TEX>${\alpha}$</TEX>-Fe<TEX>$_2$</TEX>O<TEX>$_3$</TEX> underlayer and the high coercive force and squareness were influenced by this. The crystal structure was conformed to be a Magntoplumbite symmetry with the hexagonal unit cell and the lattice constant of a increased with increasing film thickness, while c decreased

Characteristic magnetic behavior of subaerial and submarine lava units from the Hawaiian Scientific Drilling Project (HSDP‐2)

This study presents rock magnetic properties and the magnetic mineralogy of subaerial and submarine lava flows of Mauna Loa and Mauna Kea volcanoes collected from the 3109 m deep HSDP‐2 drill hole in Hawaii. Three different groups of magnetic behavior are recognized in the subaerial lava flows related to the degree of high temperature oxidation during extrusion. Group 1 shows homogenous titanomagnetite with low Xmt, low Curie temperatures (TC: 100°–200°C) and weak median demagnetizing fields (&lt; 20 mT). Further subdivision into 1a and 1b subgroups is based on the low temperature behavior of magnetic susceptibility (MS) and hysteresis loops, which indicate a contribution from ferrimagnetic Cr‐Al spinel below ca. −160°C in the 1b‐type samples. Group 2 samples, with exsolution lamellae of ilmenite in the titanomagnetites, have higher TC (480°–580°C) and higher coercive forces (20–40 mT). Group 3, the highest oxidation stage, is characterized by titanohematite‐bearing assemblages with enhanced median demagnetizing fields (35–85 mT) and a significantly different low‐temperature MS behavior. MS core logging shows a systematic variation occurs in the subaerial lava flows, directly related to the degree of high temperature oxidation and their flow morphology. Aa lava flows have higher mean MS than other lava flow types. Besides these factors, MS appears to be also affected by the magma composition of the various shield‐building stages. Mauna Loa subaerial lava flows generally show lower mean susceptibilities (4.6 ± 3 × 10−3 SI) than subaerial Mauna Kea lava flows (9.8 ± 5 × 10−3 SI). As submarine lava flows show no group 3 assemblages no high temperature oxidation influenced these rocks. Some hyaloclastites and pillow breccias show low MS (&lt; 1 × 10−3 SI), small amounts of nearly pure magnetite (TC = 580°C) and high coercive forces up to 110 mT suggesting single domain and/or superparamagnetic behavior. The controlling mechanism of the magnetic properties in the submarine lava units is the cooling and quenching rate of lava flows, which creates large grain size variations in titanomagnetites of varying compositions. Hydrothermal alteration, as described from ocean floor or Icelandic basalts, is not an important process that influences the magnetic properties in the ocean island basalts from the HSDP‐2 drill hole.

Current Status of Bonded Sm-Fe-N Anisotropic Magnets (invited)

A reduction and diffusion method (R/D) is used to make a mother alloy of Sm-Fe-N anisotropic magnets. Reduction of 0.5 wt% of samarium content compared to conventional powder increases magnetization. Milling and surface treatment improve the squareness of demagnetization curve, the aging property and the heat resistance quality. Maximum energy product of 292 kJ/m3 is obtained with the powder. High coercive force is maintainable even if the powder is exposed for 300 h in 80°C and 90 %RH. The maximum energy product of 141 kJ/m3 is obtained with an injection molded anisotropic magnet. The aging property estimated by irreversible flux loss is comparable to the conventional MQP-B magnets. The heat resistance temperature (T-5%) at which the initial irreversible flux loss becomes -5% is 125-more than 150°C for Sm-Fe-N magnets and 150-170°C for hybrid magnets.

Structure and magnetic properties of nanocrystalline alloys based on Nd 2Fe 14B obtained by various techniques

In the present work a study of phase composition and structure parameters influence on the magnetic properties of nanocrystalline Nd–Fe–B alloys was carried out. The alloys studied were produced by various techniques such as a centrifugal spraying method, melt spinning and hydrogenation disproportionation desorption recombination (HDDR) process. The alloys produced by centrifugal spraying were found to be multi-phase and contained, along with the Nd 2Fe 14B phase, particles of α-Fe and Nd-rich phase. A decrease of crystallite sizes of the magnetic phases (Nd 2Fe 14B and α-Fe) and reduction of the α-Fe amount has led to the magnetic properties refinement. The melt-spun single-phase alloy was characterized by finer crystallites and higher magnetic properties. HDDR processed alloys contained crystallites with sizes in the range of 50–100 nm, which were higher than those in the rapidly solidified alloys (25–50 nm). The HDDR processed alloys had sufficiently high coercive force, but their remanence was lower than that in the rapidly solidified powders.

Magnetic viscosity in Nd60Fe30Al10 amorphous alloys

Abstract Ferromagnetic amorphous Nd 60 Fe 30 Al 10 alloys melt spun at wheel speeds between 5 and 20 m/s exhibit hard magnetic properties, which are found to be very sensitive to the cooling conditions. The magnetization reversion mechanisms leading to the rather high coercive forces found are investigated by thermally activated magnetic relaxation experiments; the mean fluctuation field and the activation volume are measured—in specimens cooled at different rates—at the critical field for extensive magnetization reversion. These preliminary results show a qualitative agreement with the predictions of a ferromagnetic cluster model.

パルス電析によるFe-Ni系微粒子・多層膜の電気的および磁気的性質

Pulse electrodepositon is a useful technique with which it is possible to achieve atomic-scale control of the layer composition, thickness of the multilayer and the grain size in ferromagnetic films by regulating the pulse amplitude and width. It is possible to fabricate ferromagnetic films with various magnetic properties from a single electrolytic solution containing more than two kinds of metallic ions, by changing the step pulse wave. Multilayer films composed of a Ni-rich layer with high coercive force, an Fe-Ni layer with low coercive force, and a nonmagnetic Cu layer were produced by controlling the step pulse potential from a single electrolytic solution containing Fe, Ni and Cu ions. Moreover, we are able to produce thinner ferromagnetic films consisting of multiple layers with magnetic characteristics such as a wide variation in coercive force, high susceptibility, and large magnetoresistance effect by controlling the time interval of the step pulse.In this study, we investigated the relationships between the magnetic field dependence of the magnetoresistance effect and the film preparation conditions for composition-modulated Fe-Cu-Ni alloy films produced by the pulse electrodeposition method. The MR ratio observed in the film has maximum values of 3.4% and 9% at 300 K and 5 K, respectively. A highly sensitive change of the electric resistance was obtained at a low magnetic field.

Functional Effects of Carbon-Coated Iron Metal Particles for Magnetic Recording Media

Magnetic particles with finer size, higher coercive force, and lower electrical resistance are required to produce better magnetic recording media. Metal has become one of the most suitable materials for high-density magnetic recording media; however metal particles are chemically unstable and their magnetic properties such as coercive force and saturation magnetization are easily ruined. We have tried carbon coating using a chemical agent to aid the carbon to adhere to the surface of metal particles. The carbon-coated particles become chemically stable and their oxidation is gradual enough to extinguish the ignition point. Magnetic tapes prepared using the carbon-coated metal particles in the recording layer exhibit improvements in both electrical resistance and orientation properties. A decrease in the electrical resistance of about two orders of magnitude relative to conventionally prepared tapes is achieved when about 10% of the particle weight is carbon black. The squareness and orientation ratio are also raised and viscosity is lowered because the dispersibility of these particles in magnetic lacquer is better than that of the uncoated metal particles. Transmission electron microscopy photographs indicate that all of the carbon black is bound to the surface of the metal particles. © 2002 The Electrochemical Society. All rights reserved.

Simultaneous laser-magnetic field treatment of SrFe 12O 19 thin films grown by pulsed laser deposition

Strontium hexaferrite (SrFe 12O 19) thin films were grown by pulsed laser deposition on (0 0 0 1) single crystal sapphire substrates at substrate temperatures of 600 and 800 °C. Post-deposition Nd:YAG laser annealing with external magnetic field was applied. The films deposited at the higher substrate temperature were c-axis textured. Very high squareness (≈1) of the hysteresis loops was obtained for the films deposited at the lower temperature. The laser modification of the ferrite thin films produced a smooth film surface and higher coercive forces, particularly in the direction of applying the external magnetic field. The annealed films showed significant improvement of the perpendicular coercive force. The higher magnetization of the films is a result of the c-axis crystal orientation and formation of grain chains in the films.

Structure and hard magnetic properties of barium hexaferrite with and without La 2O 3 prepared by ball milling

The barium hexaferrites have been prepared by ball milling of a BaO 2 and Fe 2O 3 mixture followed by thermal heat treatments. The structure and magnetic properties were investigated using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer techniques. The effect of grain refiner was also studied and it was found that the hard magnetic properties were improved significantly. The sintered product of barium hexaferrite powders prepared from ball milling has higher coercive force than that of other barium hexaferrite made from oxide/carbonate.

Suppression of crack formation in garnet film by using a compound glass underlayer

Garnet film made as a magneto-optical medium suffers from the problem of crack formation, caused by the high temperature of the garnet film fabrication process. We solved this problem by using a compound glass with a yield point lower than the garnet heat-treatment temperature as an underlayer. This successfully suppressed the formation of cracks in the heat-treated garnet film. As a result, we obtained a garnet film recording medium with excellent crystalline structure and high coercive force.

Exchange coupling and edge pinning in vertical head sensors

Calculations which were done for an idealized geometry, showed that exchange coupling around the of a sandwich structure formed by folding the top magnetic layer around the and connecting to the bottom magnetic layer, increases the field necessary to nucleate the rotational reversal of the magnetization by a factor of more than 9. In a more realistic case, the coupling material is likely to be less uniform and somewhat irregular providing an additional contribution to the magnetization coercive force. Edge coupling is a major contributor to the high coercive force for hard edge sensors.

Inverter cores using FeMoCuSiB nanocrystalline soft magnetic alloys

High power inverter cores using nanocrystalline FeMoCuSiB alloy annealed in transverse magnetic field were developed. The new cores show excellent properties, such as low core loss and high permeability, FeMoCuSiB alloy shows a high dynamic permeability of 24381 and a low dynamic coercive force H c of 6.16 A/M measured at 20 kHz. This high permeability and low coercive force can reduce the exciting electric current, thus the magnetic bias and waveform can be improved. Low temperature rise of core is due to using two special protection cases, one case is an aluminum box, the aluminum case has some divergent vanes which can send out the heat produced by the core and the vans can also be used as a support fixed to the bedplate. Another is nylon case with some wind holes on it, the heat produced by the core can easily be sent out through the wind holes. Accordingly, the new cores are expected to be applied in many applications as 20–100 kHz, high power main transformer for power-electronic devices.

光学的手法による垂直薄膜媒体磁化過程の膜厚方向解析

Heterogeneity of the perpendicular magnetization process dependence on film depth for CoNiCrTa and CoCrTaPt perpendicular thin-film media is discussed based on a magneto-optical analysis. Results show that: (1) by means of longitudinal Kerr equipment, evaluation for separating longitudinal magnetization of a columnar structure and initial layer is possible; (2) in a perpendicular magnetization process, the top of the medium has high coercive force and high squareness compared with the bottom of the medium; and (3) the top of the medium has homogeneous magnetization thicker than 25 nm, and the bottom has a thickness of about 10 nm. The top and bottom of the medium are considered to be a columnar structure and initial layer, respectively.

極薄高融点ＷＣｒシード層による薄膜磁気記録媒体の結晶粒微細化 高Ｈｋ｀ｇｒａｉｎ´媒体における低ノイズ化

To reduce grain size while maintaining high coercive force in longitudinal thin-film media, we applied a combination of deposition of a very thin WCr seedlayer with a dry-etching process to a magnetic medium material with comparatively high magnetocrystalline anisotropy. As a result: (a) the deposition of a 0.5-nm WCr seedlayer reduced the grain size from 9.1 nm to 7.9 nm; (b) the SN ratio of the medium with 0.25-nm − 1.0-nm-thick WCr seedlayer increased by 1.5 dB due to a 20% decrease in medium noise compared with the standard medium without WCr seedlayer, caused mainly by reduction of the grain size; and (c) in the case of media with WCr seedlayer thickness less than 1.5 nm, high coercivity was maintained due to strong c-axis orientation and high thermal stability (νactKugrain/kBT > 80), enabling these media to maintain a high recording resolution. Consequently, application of this sputtering process to media with high magnetocrystalline anisotropy stability is very effective in improving SN ratio while maintaining recording resolution.

“In situ” magnetic modification of polar elastomers

The paper presents the results of the research on the effect of a hard magnetic high coercive force fillers on rubber to filler interaction in polar elastomers based compositions. The changes in Brabender plasticorder curves, temperature characteristics of the process of mixing, equilibrium degree of swelling, bound rubber content and degree of crystallization are discussed. Reassuring evidences for the realization of polar elastomers magnetic modification “in situ” without external magnetic field application are considered.