J. van Lier

MICROSTRUCTURE AND HARD MAGNETIC PROPERTIES OF NANOCOMPOSITE SM2FE15GA2CX PERMANENT MAGNETS WITH AN EXCESS OF FE PREPARED DIRECTLY BY MELT SPINNING

The nanocomposites Sm–Fe–Ga–C with low Sm contents have been prepared directly by melt spinning without a subsequent heat treatment. A highly isotropic remanence to saturation magnetization ratio of 0.6–0.7 and a relatively high coercivity of 5.5 kOe were achieved from the as-quenched ribbons. X-ray diffraction and thermomagnetic analyses show that the as-quenched ribbons consist of a magnetically hard phase Sm2Fe15Ga2Cx and a magnetically soft phase α-Fe. Transmission electron microscopy observation demonstrates that the major 2:17-type phase has larger crystallites and the crystallites of the minor phase α-Fe are smaller and located separately at the grain boundaries of the major phase. The remanence enhancement is attributed to the exchange coupling between the intergrains. Both microstructure and magnetic properties are found to depend sensitively on the substrate velocity. The effect of the microstructure on hard magnetic properties has been discussed.

Magnetic and microstructural properties of melt-spun FeGaSmC permanent magnets

Abstract The influence of an over-stoichiometric Sm content on the magnetic and microstructural properties of melt-spun Fe 15 Ga 2 Sm 2+δ C 2 alloys with δ = 0.13–0.23 has been investigated. A strong increase in the coercivity μ 0 H C up to 2.2 T at room temperature has been found with increasing δ values. Room-temperature values of the maximum energy density are (BH) max = 61.7–64.3kJ/m 3 . For elevated temperatures (T ≥ 450K) the sample with the highest Sm content (δ = 0.23) exhibits the largest values of the maximum energy density, e.g. (BH) max = 31.4kJ/m 3 at 500 K. From the reversible part of the recoil curves, the temperature dependence of the intrinsic magnetic properties J S . K 1 andK 2 has been determined. The microstructural parameters α K and N eff describing the influence of the non-ideal microstructure on the coercive field were determined from the temperature dependence of the coercive field and compared with the real microstructure.

Magnetic properties of melt-spun Sm2+δFe15Ga2C2 permanent magnets

The change in the magnetic properties of melt-spun Sm{sub 2+{delta}}Fe{sub 15}Ga{sub 2}C{sub 2} permanent magnets with variation of the Sm content {delta} has been investigated in the range of {minus}0.05{le}{delta}{le}0.20. A drastic increase in the coercive field {mu}{sub 0}H{sub C} from 1.5 to 2.2 T at room temperature has been observed for {delta}{ge}0.1. This can be understood as an influence of the Sm-rich nonmagnetic intergranular phase, occurring due to the Sm excess. Room temperature values of the maximum energy density up to (BH){sub max}=64.2kJ/m{sup 3} ({delta}=0.03) can be obtained. The samples with higher Sm contents exhibit larger values of the maximum energy density at elevated temperatures (T{ge}450K). For {delta}=0.13, a value of (BH){sub max}=31.4kJ/m{sup 3} has been observed at 500 K. The microstructural parameters {alpha}{sub K} and N{sub eff} describing the influence of the nonideal microstructure on the coercive field in the framework of the nucleation model were determined from the temperature dependence of the coercive field. {copyright} {ital 1997 American Institute of Physics.}The change in the magnetic properties of melt-spun Sm2+δFe15Ga2C2 permanent magnets with variation of the Sm content δ has been investigated in the range of −0.05⩽δ⩽0.20. A drastic increase in the coercive field μ0HC from 1.5 to 2.2 T at room temperature has been observed for δ⩾0.1. This can be understood as an influence of the Sm-rich nonmagnetic intergranular phase, occurring due to the Sm excess. Room temperature values of the maximum energy density up to (BH)max=64.2 kJ/m3 (δ=0.03) can be obtained. The samples with higher Sm contents exhibit larger values of the maximum energy density at elevated temperatures (T⩾450 K). For δ=0.13, a value of (BH)max=31.4 kJ/m3 has been observed at 500 K. The microstructural parameters αK and Neff describing the influence of the nonideal microstructure on the coercive field in the framework of the nucleation model were determined from the temperature dependence of the coercive field.

Reactions in TiO2/Ti3Al and TiO2/TiAl bilayers: application of target-factor analysis in Auger electron spectroscopy

Bilayers of TiO2/Ti3Al and TiO2/TiAl were heated up to 973 K. The resulting concentration–depth profiles were determined using Auger electron spectroscopy in combination with ion sputtering. By applying target-factor analysis it was possible to distinguish between different states of chemical bonding of the elements analysed. In both TiO2/Ti3Al and TiO2/TiAl heating causes decomposition of titanium dioxide at the bilayer interface, as revealed by the associated oxygen diffusion into the metallic layer. In a certain depth range near to the original bilayer, interface oxygen is bonded to both Ti and Al. In the original Ti3Al layer oxygen dissolves homogeneously, whereas Al2O3 was formed in the original TiAl layer, particularly in the central region. Copyright

High performance Sm2+δ Fe15Ga2C2 permanent magnets made by melt spinning and hot pressing

Hot pressing was applied to produce high performance permanent magnets from melt-spun Sm2+δ Fe15Ga2C2 ribbons. The isotropic magnets show densities up to 7.8 g/cm3, coercivities μ0JHC up to 2.01 T (15.9 kA/cm) and energy products (BH)max up to 60.3 kJ/m3 (7.58 MGOe). No texture could be observed after hot deformation at 800 °C.

Magnetic relaxation in Sm2Fe14Ga3 and Sm2Fe14Ga3C

Magnetic after-effect measurements of Sm2Fe14Ga3 and the carbide Sm2Fe14Ga3C were performed in the temperature range of 140 to 450 K. In the case of Sm2Fe14Ga3C, the relaxation spectrum is composed of two characteristic maxima at 220 and 320 K. The latter maximum is not present in Sm2Fe14Ga3 and therefore assigned to local jumps of interstitially dissolved carbon atoms while the former is attributed to hydrogen. Numerical evaluation yielded an activation enthalpy of (0.96 ± 0.02) eV and a pre-exponential factor τ0=3×10−14±0.5 s for the short-range diffusion of C atoms. The corresponding values for the short-range diffusion of hydrogen are (0.64±0.04) eV and τ0=3×10−14±1 s.

Magnetic properties of R2Fe17-xGaxC (R = Gd or Tb) compounds

The effect of Ga substitution on the structure and magnetic properties of R2Fe17C(R = Gd or Tb) compounds has been investigated by X-ray diffraction (XRD) and magnetization measurements. Samples were prepared by are-melting. XRD patterns indicate that all samples have a rhombohedral Th2Zn17-type structure, except for R2Fe9Ga8C (R = Gd, Tb), which contains a small amount of an impurity phase. The unit cell volume upsilon is found to increase monotonically with increasing the Ga concentration at a rate of 7.1 Angstrom(3) for Gd2Fe17C and 6.2 Angstrom(3) for Tb2Fe17C per Ga atom, The Curie temperature T-c shows a maximum value at about x = 3 and a minimum value at about x = 6 for both Gd2Fe17-xGaxC and Tb2Fe17-xGaxC compounds, X-ray diffraction measurements on magnetically aligned powder samples reveal a change in easy magnetization direction

Electron microscopy studies of high coercive melt-spun Sm2+δFe15Ga2C2 permanent magnets

The influence of over-stoichiometric Sm contents on the magnetic properties of melt-spun Ga stabilized Sm2Fe17 carbides has been investigated. For optimum heat treated Sm2+δFe15Ga2C2 ribbon flakes an increase of the room temperature coercivity could be observed from μ0HC=1.5 T for stoichiometric samples to μ0HC=2.2 T for δ=0.15. This effect is very interesting because of the improved temperature stability. At 500 K a maximum energy density of (BH)max=31.4 kJ/m3 for δ=0.09 can be observed. It is assumed that a Sm-rich nonmagnetic intergranular phase decouples the grains magnetically and is consequently the origin of the high coercivities of these samples. Electron microscopy studies of these melt-spun Sm2+δFe15Ga2C2 samples with different Sm contents have been performed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A broad grain size distribution (50–250 nm) is observed in the SEM, but there is no difference among samples with different Sm contents. TEM studies show no c...

Measurement of N and C diffusion in Sm2Fe17 by magnetic relaxation

Abstract Magnetic after-effect (MAE) measurements of nitrided and carburized Sm 2 Fe 17 compounds were performed in the temperature range of 140 K to 480 K. Both nitrided and carburized compounds show relaxation maxima at 285 and 300 K, respectively, which are absent in pure Sm 2 Fe 17 compounds. Therefore, these relaxation maxima are attributed to jumps of interstitially dissolved nitrogen or carbon atoms. Numerical evaluation yielded an activation enthalpy Q N (0.84±0.05) eV and a pre-exponential factor τ 0 N =3·10 −15±1 s for the short-range diffusion of N atoms. The corresponding values for the carbon diffusion are Q C =(0.91±0.05) eV and τ 0 C =1·10 −15±1 s. The carbon and nitrogen content of the samples was determined from the increase in mass during nitrogenation or carburization to Sm 2 Fe 17 N 1.2 and Sm 2 Fe 17 C 2.6 .