An ordered Fe 16 N 2 phase has been reported with iron moments as high as 3.2 μ B . It is precipitated from nitrogen martensite structures ideally containing 10.5 at.% nitrogen. Due to the highly distorted crystal structure and metastability of this phase non-equilibrium processing routes are sought to synthesize this phase. Here we report on radio frequency (RF) plasma torch synthesis which is used to produce FeN. nanoparticles quenched into a body centered tetragonal bct) structure as precursors for further annealing studies to form α“- Fe 16 N 2 phase. We have employed a Tekna PL-50 type 50 kW, RF plasma torch. A plasma gas mixture containing 40 standard liters per minute (slpm) Ar and 8 slpm Hydrogen - 70 slpm Ar gas was used as a sheath gas. Iron powder ( < 10 μm) was injected into the plasma stream using Ar flowing 15 slpm as a carrier gas. Nitrogen and Ammonia were used as a nitrogenization sources. Relatively low injection rates were used in order to achieve smaller particle sizes and thus faster quenching rates. We were able to produce particles containing up to 45 % of the quenched γ-phase. Observations based on x-ray diffraction (XRD) determination of lattice expansion and phase transition temperatures observed by differential thermal analysis (DTA) indicated that the quenched phase contains 6.5 atomic % nitrogen. Scherrer analysis of the fine particle broadening indicated that the average particle size for γ- phase is 27 nm, whereas this value is found to be 55 nm. for α-Fe. Nitrogen is well known for its grain size refinement in Fe thin films. Saturation magnetizations were found to be as low as 123 emu/g due to the presence of the nonmagnetic γ-FeN x phase.

Certain R2Co17 and R2 T14 B systems (R = a rare earth, T = Fe or Co) are of significance for use in the fabrication of high energy magnets. Improvements in these systems as high energy magnet materials are effected by partially replacing Co or T by appropriate d transition metals. A description is given of the magnetic behavior of a number of systems based on R2 Co17 and R2T14 B. Also, an account is given of recent work dealing with the systems RCo4 B and PrCo4-xFex B. The latter materials have large magnetizations and high Curie temperatures. However, they are not useful permanent magnet materials because they exhibit planar anisotropy. Results of some Auger spectroscopy studies of R2 Fe14 B systems (R = Pr,Nd or Er) are presented. This work shows the intergranular region to be rich in B, O and R. This region is undoubtedly non-magnetic, a feature which is most probably of significance in regard to the observed coercivity of R2 Fe14 B magnets.

Nd2-xPrxCo14B intermetallics crystallize in tetragonal form isostructural to Nd2Fe14B. Structural and magnetic properties of the polycrystalline materials have been determined. Room temperature magnetic measurements indicate that these intermetallics exhibit uniaxial anisotropy throughout the entire composition range. Substitution of praseodymium in Nd2-xPrxCo14B significantly enhances the anisotropy field both at 78 K and at room temperature. Magnetization versus temperature plots show spin reorientation TSR2 at 546 K for Nd2Co14B and at 668 K for Pr2Co14B. TSR2 increases linearly with composition x. The 3d sublattice anisotropy which seeks the tetragonal plane appears to dominate above these temperatures. In addition to the above, low temperature magnetic measurements demonstrate the spin reorientation in Nd2Co14B and Nd1.9Pr0.1Co14B. Further additions of praseodymium strengthen the axial anisotropy at temperatures down to 4.2 K. Effect of competing crystal field interactions and the consequences of praseodymium substitution that result in considerable increase in anisotropy field in these quaternaries are discussed.

Alloys with nominal composition LaCo7-xMx (M=Zr, or Ti and x = 0-0.6) were synthesized and characterized in the temperature range of 10-1273 K in fields up to 5 T. The experimental results show that the effects of Zr or Ti doping on the structure, phases present and magnetic properties of the LaCo7-xMx alloys are different. In the case of Zr, for as-east alloys, besides the 1-5 (CaCu5) and 1-13 (NaZn13) phases, a new phase with T-c = 1073 similar to 1173 K was detected. This new phase is probably in a hexagonal structure and shows a uniaxial anisotropy. After annealing at 1273 K, the 1-5 phase increases and almost dominates the materials when x = 0.3 similar to 0.5. It shows a strong uniaxial anisotropy with H-A = 95 similar to 135 kOe at both 300 K and 10 K. The T-c's are similar to 838 K, which is almost the same as that of LaCo5. In the case of Ti, besides the 1-5 and 1-13 phases, another new phase with Th2Zn17 structure was formed by Ti doping and almost dominates the materials when x = 0.3 similar to 0.6. This phase exhibits a uniaxial anisotropy with H-A similar to 25 kOe at both 300 K and 10 K. T-c decreases from 998 K to 901 K when the Ti content increases from x = 0.25 to x = 0.6.

RFe13−xSix (R = Pr, Nd and Gd) alloys with x = 2.5–5 have been synthesized and characterized in a magnetic field up to 17 kOe and in a temperature range 10–1173 K to ascertain whether they might be useful as high temperature, high-energy permanent magnet materials. It was found that a body-centered tetragonal (BCT) Ce2Ni17Si9-type structure forms in PrFe13−xSix alloys when x ⩾ 4. The Curie temperatures Tc of this BCT phase are in a range 50–90 K, higher than that of the corresponding PrCo13−xSix BCT phase (∼ 20 K). The PrFe13−xSix alloys with x⩾ 4 show spin reorientation at cryogenic temperatures (15–47 K) and exhibit significant coercivity in loose powder samples below their spin-reorientation temperature. Using the information about the magnetization of LaFe13−xSix BCT alloys, one can estimate the moment of Pr ion in PrFe13∼-xSix alloys. It is found to be very close to that in PrCo13−xSix BCT alloys, around 2 μ2/atom. For RNd or Gd, the RFe13−xSix alloys occur only as mixtures of RFe2Si2, R(Fe, Si)11 and FeSi. The Ce2Ni17Si9-type structure cannot be formed in these alloys even when x = 5. The low Tc for the PrFe13−xSix alloys precludes their use as a permanent magnet material, except perhaps at low temperature.

LaCo9+deltaSi4 and LaCo8.5+deltaSi4.5 alloys with delta=0 to 4 have been synthesized and characterized. The stoichiometric alloys (delta=0) have low T-c and small moments, whereas the alloys with delta not equal 0 have larger T-c and magnetization. (C) 1996 American Institute of Physics.

Crystal structure and magnetic properties of ternary compounds based on R2Fe14Si2 (off-stoichiometric R2Fe17 type) were investigated. Results of the powder x-ray-diffraction indicated that the compounds examined in this study crystallize in the rhombohedral Th2Zn17-type structure when R is Nd or Gd and in the hexagonal Th2Ni17-type when R is Y, Dy, Ho, or Er. The Curie temperature T(C) and room-temperature saturation magnetization M(s) of R2Fe14Si2 system range from 465 to 572 K and 65 to 150 emu/g, respectively. The behavior of Tc is found to follow the root of the de Gennes function and can therefore be ascribed to the strength of the rare-earth-iron exchange interaction. The average magnetic moment of Fe in R2Fe14Si2 is estimated to be approximately 2.0 mu(B) at 77 K. Addition of Si in the binary R-Fe lattice induced a large uniaxial magnetic anisotropy at room temperature in some alloys. Results of M vs T for Er2Fe14Si2 indicate a spin reorientation transition at about 100 and 35 K. Dy2Fe14Si2 and Ho2Fe14Si2 exhibit a remarkable magnetic hardening at low temperatures.

The liquidus projection surface and the isothermal section at 1000 °C of the Co-Pr-B (Co-rich) ternary phase diagram have been determined. The binary and ternary intermetallics (Pr2Co17, PrCo5, Pr5Co19, Pr2Co7, PrCo3, PrCo2, C03B, C02B, CoB, P2Co14B, PrCo4B, PrCo12B, Pr3Co11B4, and Pr2Co7B3) that were examined in the Co-rich portion of the Co-Pr-B ternary phase diagram were found to be true line compounds (no detectable solid solubility). The primary solidification phase field of the Pr2Co14B intermetallic compound shares boundaries with the primary solidification phase fields of αCo, Pr2Co17, PrCo5, P1-C04B, and PrCo12B6 intermetallics. There are eight reactions associated with the Pr2Co14B intermetallic compound: two ternary eutectic reactions (E1 = Liquid ↔ Pr2Co14B + PrCo12B6 + PrCo4B and E2 = Liquid ↔ Pr2Co14B + PrCo12B6 + αCo), two pseudobinary eutectic reactions (e3 = Liquid ↔ Pr2Co14B + PrCo4B and e4 = Liquid ↔ Pr2Co14B + PrCo12B6), three ternary quasi-peritectic reactions (P1 = Pr2Co17 + Liquid ↔ Pr2Co14B + αCo, P2 = Pr2Co17 + Liquid ↔ PrCo5 + Pr2Co14B, and P3 = Pr2Co14B + Liquid ↔ PrCo4B + PrCo5), and one pseudobinary peritectic reaction (p8 = Pr2Co17 + Liquid ↔ Pr2Co14B). The composition of the magnetically important Pr2Co14B intermetallic falls inside the primary solidification phase field of the Pr2Co17 intermetallic. The reaction through which the Pr2Co14B is produced is therefore the pseudobinary peritectic reaction Pr2Co17 + Liquid ↔ P2Co14B. The PrCo12B6 and PrCo4B compounds are found to form congruently from the melt At the temperature of 1000 °C and depending on the alloy composition, the P2Co14B intermetallic can be found in solid-state thermodynamic equilibrium with one or two of the following phases: αCo, Pr2Co17, PrCo5, PrCo4B, and PrCo12B6. The obtained information about the Co-Pr-B phase diagram can be used to explain correctly all the phases present in the P2Co14B-based permanent magnets. The present work also emphasizes the extreme importance and usefulness of thermomagnetic measurements as an aid in the determination of phase diagrams that involve ferromagnetic phases.

Magnetic and structural properties of Fe3GeNx have been investigated. The fcc phase of Fe3Ge absorbs nitrogen up to x=0.24. As the result of absorption, the Curie temperature and room temperature magnetization decrease from 736 K and 137 emu/g to 614 K and 74 emu/g respectively. The hcp phase of Fe3Ge, however, transforms to either fcc or tetragonal phase or a combination of these upon nitrogenation. The tetragonal nitride phase forms at a reaction temperature of 600 C to 650 C in a flowing atmosphere of ammonia. This phase is paramagnetic at room temperature and appears to order antiferromagnetically below 100 K.

Fe 3 Ge crystallizes in two modifications. The high temperature phase exhibits a hexagonal crystal structure of the Ni 3 Sn-type with the space group P6 3 /mmc. The low temperature phase crystallizes in the face centered cubic (FCC) Cu 3 Au-type with the space group Pm 3 m. Fe 3 Ge absorbs nitrogen under mild conditions of temperature and pressure. A few years ago, Stadelmaier et al. and Boller reported that nitrogenation of Fe 3 Ge results in a change in the crystal structure to the tetragonal (FCT) Cr 3 AsN-type with the space group 14/mcm. Magnetic properties of the nitrides of Fe 3 Ge have not been published in the literature. The objectives of the present work are to optimize the conditions for the formation of the nitrides of Fe 3 Ge and examine their magnetic and structural properties. We also propose to extend this work to include other transition metals. In view of the considerable interest of the nitrides of rare earth-transition metal intermetallic compounds, it seemed pertinent to examine pure transition metal-based nitrides.

Magnetic and structural properties of Fe/sub 3/GeN/sub x/ have been investigated. The FCC (face centered cubic) phase of FeGe absorbs nitrogen to x=0.24. As a result of absorption, the Curie temperature and room temperature magnetization decrease from 736 K and 137 emu/g to 614 K and 74 emu/g, respectively. The HCP (hexagonal close packed) phase of Fe/sub 3/Ge, however, transforms to either FCC tetragonal phase, or a combination of these upon nitrogenation. The tetragonal nitride phase forms at a reaction temperature of 600 degrees C to 650 degrees C in a flowing atmosphere of ammonia. The phase is paramagnetic at room temperature and appears to order antiferromagnetically below 100 K. >