Alnico Research Articles

Tailoring exchange coupling and phase separation in Fe-Co-Mn nanocomposites

An intriguing pathway for the realization of metallic, rare-earth-free magnets is described. Creation of a so-called “exchange-bias” permanent magnet is contemplated that mimics the microstructure of Alnico magnets, comprised of FeCo-based precipitates that are separated by a metallic antiferromagnetic phase that replaces non-magnetic NiAl-rich phase of alnico. In this manner, the existing shape anisotropy is augmented by exchange-bias anisotropy through interphase coupling, providing enhanced coercivities. As a proof of concept, nanocomposite alloys have been fabricated from rapidly solidified Fe34Co33Mn33 ribbons that phase separate into an antiferromagnetic Mn-rich γ-phase and ferromagnetic α-FeCo nanoprecipitates upon post-solidification processing. A progressive enhancement of coercivity, remanence, and exchange bias at T < TN in the ferromagnetic-antiferromagnetic nanocomposite is noted upon annealing, with maximum properties realized at Tann ≈ 673 K for 30 min. Optimization of the microstructure of these Fe-Co-Mn-based alloys is anticipated to be accompanied by improved magnetic performance that could contribute to the development of next-generation permanent magnets.

Magnetism of rapidly quenched rhombohedral Zr2Co11-based nanocomposites

The effect of quench rate and Zr content on nanostructure and magnetic properties of melt-spun ZrxCo100−x(x = 16–21) is investigated. High quench rate favours the formation of rhombohedral Zr2Co11, which is the hard phase. The coercivity increases with an increase in quench rate. Zr addition in limited amounts decreases the grain size of magnetic phases, which may promote the effective exchange coupling of soft magnetic phases. Therefore, coercivity and maximum energy product of Zr2Co11-based materials are significantly enhanced. The best magnetic properties,iHc = 3.0 kOe and (BH)max = 4.6 MG Oe, which are the highest reported values among Co–Zr binary alloys, are achieved for x = 18. The temperature coefficients of coercivity and remanence between 100 and 380 K are −0.05% K−1, comparable to those of alnico magnet.

Accurate Measurement of Magnetic Properties of Nd-Fe-B Sintered Magnets With High Coercivity

To obtain the accurate magnetic properties of Nd-Fe-B sintered magnets with high coercivity ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cJ</sub> ), we have compared a pulsed-field magnetometer (PF) method with a hysteresis graph (HG) method using an extra large-sized electromagnet. To prevent the effects of machining on magnetic properties in small samples when making measurements of the accurate hysteresis and demagnetization curves, cylindrical samples used in the experiment were kept at a constant common diameter of 10 mm. This was necessary to correct the demagnetizing field and the effect of eddy current for the PF and the magnetization distortion for the HG methods. Reliable calibrations and corrections of the magnetization and the magnetic field were very important. Furthermore, it was essential that the longer length ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> ) of the sample be magnetized uniformly for both the methods. To correct the demagnetizing field and obtain exact differential susceptibility near <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cJ</sub> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> of the sample had to be more than 14 mm for the PF method. Because the saturation magnetization of the Nd-Fe-B sintered magnet was almost equal to that of the cast anisotropic AlNiCo magnet, the correction of magnetization distortion for the HG method using the AlNiCo magnet of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> = 21 mm, which was the same size of the sample, was most suitable in the experiment compared with the other conditions.

Abstract 8572: Enhanced Angiogenesis By Transplantation Of iPS Cell-derived Flk-1 + Cell Sheet Created By A Novel Magnetic Tissue Engineering Method

Background: Therapeutic angiogenesis using cell transplantation represents a novel strategy for severe ischemic diseases, but some patients had poor response to angiogenic cell therapy. Therefore, alternative cell source and cell application strategy have been extensively searched. Induced pluripotent stem cells are expected as one of powerful tools for regenerative medicine. We investigated a therapeutic potential of iPS cell sheet created by a novel magnetite tissue engineering technology for reparative angiogenesis. Methods and Results: Flk-1 + cells, as a vascular progenitor marker were induced from mouse iPS cells after 5 day of culture. Flk-1 + cells were purified by FACS sorting, and these cells differentiated into CD31 + endothelial and α-SMA + smooth muscle cells. Sorted Flk-1 + cells incubated with magneticnanoparticle-containing liposomes (MCLs) were cultured. MCL-labeled Flk-1 + cells were mixed with diluted extracellular matrix (ECM) precursor, and a magnet was placed on the reverse side. Magnetized iPS cell-derived Flk-1 + cells formed multilayered cell sheet after 24h incubation period. Nude mice were subjected to unilateral hind limb ischemia and separated into 3 groups. The constructed Flk-1 + cells- or Flk-1 − cells- sheet placed on the ischemic adductor muscles using the Alnico magnet before skin closure. For the control group, ECM precursor gel was layered onto the ischemic tissues. Blood flow recovery and the extent of angiogenesis were assessed by a laser doppler blood flowmetry and capillary density. The Flk-1 + cell sheet group had a greater angiogenesis in ischemic tissues compared to the control and Flk-1 − cells sheet groups (p&lt;0.05). The angiogenic and tissue-preserving effects of Flk-1 + cell sheets were attributable to an increased expression of VEGF mRNA in ischemic tissues. We did not detect formation of any tumors in Flk-1 + cells, but not in Flk-1 − cells, transplanted mice at least until post-operative day 60. Conclusions: Implantation of iPS cell-derived Flk-1 + cells has augmented ischemia-induced angiogenesis. iPS cell-derived Flk-1 + cell sheet created by the novel magnetic nanoparticle-based tissue engineering technology would represent a new modality for therapeutic angiogenesis and tissue regeneration.

Anisotropic local structure of decagonal quasicrystals by DAFS

Diffraction anomalous fine structure (DAFS) analyses were performed on Al–Ni–Co (ANC) and Al–Ni–Fe (ANF) decagonal quasicrystals at the K-edges of Ni, Co and Fe. In ANC, an order–disorder phase transition with anisotropic atomic short-range order (SRO) is clearly recognizable at high temperature. During in situ observation, a zigzag correlation along the periodic direction developed during the early stage of ordering. Far above the phase transition temperature, this weak correlation along the periodic direction is independent of other correlations along the quasiperiodic one. In ANF, SRO of Fe developed along the quasiperiodic direction, although the local environment of Ni was almost random.

ChemInform Abstract: Rare-Earth Permanent Magnets. New Magnet Materials and Applications

The introduction of rare-earth permanent magnets based on samarium-cobalt in about 1970, and neodymium-iron-boron magnets in the mid-nineteen eighties, has ushered in a new era in hard magnetic materials. This has resulted in a dramatic improvement in permanent magnet performance, with neodymium-iron-boron (Nd2Fe14B) magnets having a magnetic energy product up to an order of magnitude greater than those of Alnico and ferrite magnets, with high remanence and coercive force. The search for new permanent magnet materials has led to further interest in rare-earth-iron intermetallic compounds modified by the introduction of interstitial atoms such as nitrogen or carbon. We discuss `What makes a good permanent magnet’, in the context of the crystal structure and the magnetic properties of rare-earth-iron intermetallic alloys that are candidates for new permanent magnet materials. The methods for producing these new candidate magnet materials, including arcmelting under an atmosphere of argon, high-energy ball-milling (HEBM), mechanical alloying, melt-spinning and HDDR (hydrogenation, disproportionation, desorption, recombination) are reviewed. Examples of high efficiency electric motors, which use rare-earth permanent magnets, developed by the School of Electrical Engineering, University of Technology, Sydney, and the CSIRO Division of Telecommunications and Industrial Physics are given.

Alnico thin films with high coercivities up to 6.9 kOe

The spinodal decomposition has been investigated in Alnico thin films prepared by sputtering. The as-made bcc thin films were heat treated both by the complex heat treatment of bulk Alnico magnets and by a simple annealing at different temperatures in the range of 600-900 °C. The simple heat treatment gave a coercivity of 2.6 kOe at 600°C and 6.9 kOe at 800°C. The maximum coercivity observed is approximately ten times larger than the bulk Alnico V value. Electron diffraction patterns can be mostly indexed to a new fcc phase with a=7.79 Å. The traditional Alnico heat treatment gave a similar coercivity (6.7 kOe after full heat treatment) and similar diffraction patterns. The coercivity was found to depend strongly on the film thickness. In samples with thickness above 100 nm, the coercivity declined dramatically and at 150 nm it was only 500 Oe. These findings suggest structural transformations in films which are drastically different from the spinodal decomposition observed in bulk Alnico.

Development of Novel Magnetic Encoder and Vector Control Method for Servo Control of High-Speed Motor

This paper presents a novel unipolar magnetic encoder and a new Vector control method of AC servo which can enable the feedback of the rotor position with high accuracy in high speed occasion. The signal generator of encoder consists of three pairs of semiconductor hall elements and a rotor of alnico magnet with one pair of poles. This encoder is featured with the operation module and the communication module to transmit an angular data in the form of asynchronous serial transfer protocol. Besides, a delay compensation algorithm is proposed to ensure the accurate estimation of instant angular position and the estimation error is also analyzed. At last, an experimental apparatus was built for a 600W, 4 pairs of pole, at rated speed 20,000min-1, permanent-magnet synchronous motor drive and the proposed vector control scheme has been implemented. The experiment results supported the validity of the proposed magnetic encoder and vector control method for high-speed AC servo control within 0.05 % error of revolving speed.

Study of γ-ray irradiation effect on permanent magnets

Irradiation damage of FeCrCo, AlNiCo, SmCo, and NdFeB permanent magnets was investigated by using γ-ray irradiation. Results of magnetic property measurement show that FeCrCo and NdFeB have more demagnetization than AlNiCo and SmCo. X-ray diffraction analysis shows that γ-ray irradiation leads to the increase of FeCrCo crystal mismatch and decrease of AlNiCo ordering degree. The investigations by positron annihilation spectroscopy technique show that the defects in AlNiCo and SmCo increase after γ-ray irradiation. The defects induced by γ-ray irradiation in NdFeB magnets are not the main source that leads to partial demagnetization. The irradiation resistances of these magnets are discussed in detail considering the thermal stability, coercivity mechanisms, and defect damage.

Performance and applications of a small PM generator

AbstractThis paper presents a high‐speed low‐power small permanent magnet (PM) generator for aerospace applications where environmental requirements are very severe. Since Alnico magnet material has a low temperature coefficient of remanent flux density and maximum service temperature, it is suitable for the application. Furthermore, the main disadvantage of PM generators is the difficulty of output voltage regulation to compensate for speed and load variation, due to the lack of a simple means of field control. Hence, a circuit is used to connect to the generator to provide a fixed dc voltage to the load. The steady‐state performance is analyzed by the finite element (FE) method. Experimental tests are conducted to verify the FEM predictions. Agreement between FE analysis work and testing results is good. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Magnetic nanowires as permanent magnet materials

We present the fabrication of metallic magnetic nanowires using a low temperature chemical process. We show that pressed powders and magnetically oriented samples exhibit a very high coercivity (6.5kOe at 140K and 4.8kOe at 300K). We discuss the magnetic properties of these metamaterials and show that they have the suitable properties to realize “high temperature magnets” competitive with AlNiCo or SmCo permanent magnets. They could also be used as recording media for high density magnetic recording.

&lt;I&gt;In Situ&lt;/I&gt; Observations of Magnetization Process in Alnico Magnets by Electron Holography and Lorentz Microscopy

The magnetic microstructure of Alnico 5 and Alnico 8 and their magnetization process were investigated systematically at a nanometer scale by means of electron holography and Lorentz microscopy. In particular, the magnetization process in Alnico alloys was visualized for the first time by utilizing a sharp magnetic needle made of sintered Nd2Fe14B in a transmission electron microscope. It was found that the direction of lines of magnetic flux changed at the boundaries between the � 1 and � 2 phases which were aligned in the direction of the magnetic field applied in the thermomagnetic treatment. In the Lorentz microscope image, these boundaries were observed as white lines and black bands, whose shapes reflected the difference in the shape anisotropy between Alnico 5 and Alnico 8. With an increase in the magnetic field induced by the magnetic needle, the magnetization direction of the domains magnetized in the direction opposite to that of the approaching needle was reversed, and finally a large reversed domain was formed. In both Alnico 5 and Alnico 8, it was shown that the magnetization process was accomplished through an entire magnetization reversal in each grain of the � 1 phase.

Electrowinning of cobalt from sulphate solutions

This paper reports an account of study conducted on optimization of the process parameters for electro-winning of cobalt from cobalt sulphate solution. Effect of parameters such as bath composition, temperature, current density, agitation etc. on the voltage requirement, current efficiency and power efficiency of cobalt electro-deposition was explored. A maximum current efficiency of 97% was attained with an electrolyte composition of 60 g/L Co, 15 g/L Na 2SO 4, at a temperature of 60 °C, a pH of 4.0 and a cathode current density of 400 A/m 2. The energy consumption was 3.0 kWh/kg of Co deposited. The optimum conditions so established were test examined for recovery of cobalt values from leach liquors generated on processing of Alnico magnet scrap, cemented carbide tool scrap and spent hydrogenation catalyst. The cathode current efficiency ranged from 86% to 94% due to lower concentration (25 to 40 g/L) of cobalt concentration in the processed leach liquor.

Microwave Absorbers Prepared with Alnico Magnets

We suggest a cast Alnico magnet as a new microwave absorber. The proposed Alnico microwave absorber shows advanced microwave absorption properties of 24 dB at 13.3 GHz for the thicknesses of 1 mm We also investigated the effects of the carbon, which qjfects strongly to microwave absorption in Alnico magnet microwave absorbers. Central frequency shifts toward lower frequency with increasing Alnico content which is related to the frequency to show tan 8 > 1. Also, we investigated the sample thickness dependence on the microwave absorption properties.

Al 2O 3 coated α-Fe solid solution nanocapsules prepared by arc discharge

Al 2O 3 coated α-Fe solid solution nanocapsules are prepared by arc-discharging a bulk AlNiCo permanent magnet. The size of the nanocapsule is in range of 3–300 nm and the thickness of the shell is 1–6 nm. Al atoms in the AlNiCo magnet form the shell of amorphous Al 2O 3 to prevent the nanocapsules from further oxidation. The magnetic properties of saturation magnetization J s=85 A m 2/kg and coercive force jH c =27.5 kA/m are achieved for the nanocapsules.

Studies on Processing of an Alnico Scrap

This paper presents the results of research and development work on processing of alnico scrap, a secondary resource of nickel and cobalt, generated during the manufacturing of alnico magnets. The scrap contains 8–10% nickel, 10–12% cobalt, 32–50% of iron, 8–10% aluminium, 2% copper and remaining silica. Various processes such as acid leaching, aqueous chlorine leaching, salt roasting and cupric chloride leaching were studied in detail. Of these cupric chloride leaching was found to be most effective with respect to recovery and purity. It has been possible to obtain pure nickel and cobalt salts by cupric chloride leaching of the scrap, solvent extraction and precipitation of the salts. The overall recovery by the above process was almost 99%.

Studies on Processing of an Alnico Scrap

This paper presents the results of research and development work on processing of alnico scrap, a secondary resource of nickel and cobalt, generated during the manufacturing of alnico magnets. The scrap contains 8-10% nickel, 10-12% cobalt, 32-50% of iron, 8-10% aluminium, 2% copper and remaining silica. Various processes such as acid leaching, aqueous chlorine leaching, salt roasting and cupric chloride leaching were studied in detail. Of these cupric chloride leaching was found to be most effective with respect to recovery and purity. It has been possible to obtain pure nickel and cobalt salts by cupric chloride leaching of the scrap, solvent extraction and precipitation of the salts. The overall recovery by the above process was almost 99%.

Disorder diffuse scattering of decagonal quasicrystals

Diffuse scattering in decagonal phases is due to deviations from strict aperiodic and periodic order in the quasiperiodic plane and along the unique direction, respectively. Results from X-ray (synchrotron) and neutron diffraction experiments, mainly carried out with decagonal Al–Ni–Co, are presented. Most prominent are diffuse maxima, diffuse streaks, phason affected reflection profiles, and diffuse layers perpendicular to the unique axis. Disorder models in decagonal qc-structures, in particular lamellar domain-like ordering in super-space are outlined. The terms structure and phase in context with disordered structures are discussed.

High-performance electric machines for renewable energy generation and efficient drives

Advances in permanent magnets, electronics and design techniques over the past thirty years have led to the development of a new generation of electric machines. Sintered rare-earth neodymium–iron–boron magnets have a magnetic energy product up to an order of magnitude larger than those of alnico and ferrite magnets, with high remanence and coercive force. Coupled with new smart power electronics and the use of advanced computer aided design optimisation, the new machines are of high efficiency and/or compact size. Some state of the art developments of high-performance machines are reviewed with particular examples drawn from a number of novel designs developed by UTS and CSIRO.

Rare-Earth Permanent Magnets: New Magnet Materials and Applications

The introduction of rare-earth permanent magnets based on samarium-cobalt in about 1970, and neodymium-iron-boron magnets in the mid-nineteen eighties, has ushered in a new era in hard magnetic materials. This has resulted in a dramatic improvement in permanent magnet performance, with neodymium-iron-boron (Nd2Fe14B) magnets having a magnetic energy product up to an order of magnitude greater than those of Alnico and ferrite magnets, with high remanence and coercive force. The search for new permanent magnet materials has led to further interest in rare-earth-iron intermetallic compounds modified by the introduction of interstitial atoms such as nitrogen or carbon. We discuss `What makes a good permanent magnet’, in the context of the crystal structure and the magnetic properties of rare-earth-iron intermetallic alloys that are candidates for new permanent magnet materials. The methods for producing these new candidate magnet materials, including arcmelting under an atmosphere of argon, high-energy ball-milling (HEBM), mechanical alloying, melt-spinning and HDDR (hydrogenation, disproportionation, desorption, recombination) are reviewed. Examples of high efficiency electric motors, which use rare-earth permanent magnets, developed by the School of Electrical Engineering, University of Technology, Sydney, and the CSIRO Division of Telecommunications and Industrial Physics are given.