Fernando José Gomes Landgraf

Additional ferromagnetic phases in the FeNdB system and the effect of a 600°C annealing

Abstract In the FeNd system an additional ferromagnetic phase with Tc = 245 ± 10 °C is found. In the ternary FeNdB system, magnetic analysis shows two ferromagnetic phases with Tc = 245 and 285 °C in as-cast alloys, in addition to Fe14Nd2B. Those phases are formed through the eutectic solidification of a neodymium-rich liquid at the boron-poor side of the system, suppressing the formation of Fe14Nd2B. An annealing at 600 °C dissolves the phase with Tc = 245 °C and develops Fe14Nd2B. This results in an Hci increase from 3.9 kOe in the as-cast to 14.1 kOe in the annealed condition for an Fe-80at.%Nd-5at.%B alloy. This suggests that the dissolution of additional ferromagnetic phases in the intergranular regions of sintered FeNdB magnets might be the positive effect of the 600 °C annealing.

The effects of synthesis variables on the magnetic properties of coprecipitated barium ferrite powders

Barium ferrites (BaFe12O19) are largely used for permanent magnets, mostly because of the adequate combination of low cost and good magnetic properties. These ferrites are usually obtained by the ceramic method; however, many chemical methods have been investigated. Among these methods, the coprecipitation is the most suitable, mainly because of its simplicity as compared to the other ones. In this work, BaFe12O19 was prepared by coprecipitation, changing the sequence of addition of the reagents, and the calcination temperature and time. The X-ray diffraction patterns of the calcined samples show the formation of BaFe12O19 at temperatures as low as 8001C. The ferrite powders obtained by coprecipitation have better magnetic properties than those obtained by the ceramic method, with an intrinsic coercivity value of 440 kA/m (5.5 kOe). r 2002 Elsevier Science B.V. All rights reserved.

Solidification and solid state transformations in FeNd: A revised phase diagram

Abstract A new stable ferromagnetic phase is found to exist in the binary FeNd system, with composition Fe-22.8at.%Nd and Tc = 230°C. A revised phase diagram is presented. A metastable ferromagnetic phase with Tc = 245°C is found to occur in arc-melted and differential thermal analysis (DTA) samples, with different eutectic morphologies. The transformation of this phase in binary FeNd was investigated. The double peak thermal events occurring upon the solidification of the DTA samples are discussed.

The influence of cutting technique on the magnetic properties of electrical steels

Magnetic permeability and losses at 1.5 T of a 2% Si non-oriented fully processed electrical steel Epstein strip, cut by different techniques (punching, guillotine, laser and photocorrosion), have lower values at the as-cut condition, when compared to after annealing. Permeability at 1.5 T showed to be more affected by cutting than the losses. Photocorrosion is slightly less harmful, but annealing did not improve it as much as it did to samples cut with guillotine.

Magnetic properties of coprecipitated barium ferrite powders as a function of synthesis conditions

Barium ferrite is widely used as a permanent magnet because of its large coercivity and low cost. The usual route to produce barium ferrites is the ceramic method. In order to overcome the detrimental milling effects in the magnetic properties, ferrite powders were obtained by coprecipitation. This method can produce high purity materials with a narrow particle size distribution. In this work, the effects of the pH during coprecipitation, the molar ratio (Fe/Ba), and calcination temperature on the magnetic properties were investigated. The products were characterized by differential thermal analysis, X-ray diffractometry, scanning electron microscopy and thermomagnetic analysis. The magnetic properties were evaluated by vibrating sample magnetometry. Very fine particles with intrinsic coercivities up to 392 kA/m (4.92 kOe) were achieved.

Magnetic and structural characterization of Nd5Fe17

A new stable compound in the Nd–Fe system has been identified as Nd5Fe17. The crystal structure belongs to the hexagonal space group P63/mcm, with a=2.0214(8) nm and c=1.2329(8) nm, and with 12 formula units per unit cell. This compound is a ferromagnet with Tc = 503 K and magnetization 162 emu/g at 4.2 K. Mossbauer spectra have been measured and fitted with five Fe sites, yielding an average Beff=26.5 T at room temperature, from which an average Fe moment of 1.83 Bohr magnetons is deduced. X‐ray powder diagrams from magnetically aligned samples suggest basal anisotropy.

Losses and permeability improvement by stress relieving fully processed electrical steels with previous small deformations

The strong increase in the 1.5 T total losses of a 2.2% Si electrical steel, when a small plastic deformation is applied, is almost exclusively due to the increase in its quasi-static hysteresis loss. Stress relieving at 700°C promoted no change in the grain size, a significant reduction of 1.5 T total losses and increased permeability, which did not reach, however, the non-deformed values. The anisotropy of total losses of the annealed samples is concentrated in the high-induction component of the hysteresis loss.

Chemical composition and coercivity of SmCo5 magnets

The effects of alloy composition and heat treatment on the intrinsic coercivity iHc of SmCo5 magnets were studied. Alloys having six chemical compositions near that of stoichiometric SmCo5 were used to produce magnets via the usual powder metallurgy techniques. Magnets were either as sintered (1150 °C) or sintered (1150 °C) and treated at 850 °C. The substantial increase in iHc due to the 850 °C heat treatment occurs reversibly and with a negligible change in lattice parameters, Curie temperature Tc and anisotropy field HA. Quantitative metallography and thermomagnetic measurements showed that the microstructural constituent present in addition to the SmCo5 phase in hyperstoichiometric alloys is composed of both the Sm2Co7 phase and the Sm5Co19 phase. Measurements of magnetization in dc magnetic fields up to 33 T suggest that HA is around 53 T, considerably higher than previously reported values. The coercivity of the magnets is discussed in terms of thermal equilibrium populations of lattice defects.

Effect of plastic deformation on the magnetic properties of non-oriented electrical steels

Total loss increase in electrical steels due to plastic deformation is mainly concentrated in hysteresis loss, while classical and anomalous components show a slight decrease. Deformation increases both low-induction and high-induction components. While the mechanical properties show a smooth evolution with the deformation, the magnetic properties show a large difference even at only 0.5% elongation.

Separating Components of the Hysteresis Loss of Non-Oriented Electrical Steels

This paper shows that the separation of quasi-static hysteresis losses into two components, one related to Low Induction and other to High Induction levels. The separation line between those two regions has been arbitrarily chosen as the induction at maximum permeability. Results show that the grain size has stronger effect on the low induction component, while the high induction component is more sensitive to sample measuring direction. This may provide basis for better materialsproperties correlation modeling and product development.