W.E. Wallace

Structure and magnetic properties of SmCo7−xZrx alloys (x=0–0.8)

The alloys with composition of SmCo7−xZrx(x=0–0.8) were synthesized and characterized in the temperature range of 10–1273 K and at fields up to 5 T. The experimental results show that a small amount of Zr substitution can contribute to a stabilization of the TbCu7 structure, and improve magneto-anisotropy Ha from 90 kOe for x=0–180 kOe for x=0.5 at room temperature, and from 140 kOe for x=0–300 kOe for x=0.5 at 10 K. It is probable that Zr may partly replace a dumbbell of Co atom pair in these alloys. The phase transition between CaCu5, TbCu7, Th2Zn17, and Ce2Ni7 at different heat treatment conditions was also discussed.

Magnetic characteristics of R2(Fe, Co)14B systems (R = Y, Nd and Gd)

Abstract R 2 (Fe, Co) 14 B compounds (R = Y, Nd and Gd) were prepared in high purity. The magnetic behavior of R 2 (Fe, Co) 14 B compounds is reported over the temperature range 4 to 300 K. The effects of Fe substitution by Co on the saturation magnetization, Curie temperature and anisotropy are presented. The spin-reorientation temperature is lowered as Co replaces Fe. This also results in a reduced cone angle. The R 2 Fe 14− x Co x B alloys crystallize in the tetragonal structure over the entire concentration range of 0 ⩽ x ⩽ 14. When Fe is substituted by Co, the Curie temperature increases significantly, the saturation magnetization increases to a maximum value around x = 2, and the anisotropy becomes planar for R = Y and Gd. The Nd 2 (Fe, Co) 14 B systems all exhibit uniaxial anisotropy at room temperature and Nd 2 Co 14 B is strongly uniaxial at 77 K. The Nd 2 (Fe, Co) 14 B systems are conical at 77 K.

Magnetic properties of RCo4B compounds where R = Y, Pr, Nd, Gd and Er☆

Abstract The magnetic properties of RCo 4 B compounds (R = Y, Pr, Nd, Gd and Er) were studied in the temperature range 4.2–1000 K. The compoun with R = Y, Pr and Nd are ferromagnetically ordered. The reciprocal susceptibility, χ -1 , for R = Pr follows a modified Curie-Weiss law. The compounds with R = Gd and Er show a ferrimagnetic-type ordering. Above the Curie points the χ -1 vs. T curves may be described by a hyperbolic law of Neel-type. The mean molecular field coefficients characterizing the exchange interactions inside and between magnetic sublattices were determined. These are correlated with the mean magnetic contributions of cobalt atoms.

Metal‐bonded Sm2Fe17‐N‐type magnets

A number of metal‐bonded Sm2Fe17‐N magnets have been fabricated. These magnets exhibit iHc = 5.1–17.0 kOe, Br = 6.4–8.4 kG, (BH)max=5.0–10.8 MGOe, Tc = 757 K, and ρ=6.2–6.7 g/cm3. Powder metallurgical techniques have been employed with a mixture of powdered Sm2Fe17‐N and Zn, Sn, or In. Heat treatment is carried out in the temperature range of 160–450 °C in a N2 atmosphere at pressures ranging from 0–900 psi. The effects of Zn, Sn, and In contents and heat treatment conditions on the magnetic properties have been studied. Zn as the binder significantly enhances the coercivity iHc from 1.8–2.5 kOe for Zn‐free magnets to 5–17 kOe for 9–20‐wt. % Zn‐containing magnets. The Fe‐Zn phase, FeZn4, and/or Fe3Zn7, formed during heat treatment, may play an important role in producing a high coercivity. Sn‐bonded magnets exhibit significant coercivity, whereas the In‐bonded materials do not. The coercivity behavior is discussed in terms of the chemistry of the system.

Magnetic and structural properties of SmTiFe11-xCox alloys

Abstract SmTiFe11-xCox (0⩽x⩽11) alloys were synthesized and studied by X-ray, SEM, EDXS and magnetometry at fields up to 90 kOe in the temperature range of 4.2–1100 K. It is established that almost single-phase materials exhibiting a ThMn12 type structure can be formed only for x

Synthesis and characterization of Fe16N2 in bulk form

Using molecular beam epitaxy and ion implantation, Japanese workers have formed Fe16N2 in thin Fe films. They report a large magnetic induction for this nitride, ≥2.8 T. In the present study, Fe16N2 has been prepared in bulk form by treating Fe powder with NH3/H2 gas mixtures at temperatures in the range 660–670 °C. The γ phase alloy, which forms under these conditions, was quenched to room temperature to form the α’‐Fe‐N phase and then heat treated at 120–150 °C to form the α‘‐Fe‐N phase. The α’ phase has been prepared in 80% purity, the other phase being nonmagnetic γ‐Fe‐N. The α‘ phase has been prepared in 50% purity, the impurity phases being α‐Fe and γ‐Fe‐N. Magnetic measurements give saturation magnetizations at room temperature of 250±10 emu/g (2.6μB/Fe) for the α’ phase, 285±10 emu/g (2.9μB/Fe) for the α‘ phase, and essentially zero for the γ phase. Mossbauer measurements confirm that nitrogen austenite is nonmagnetic. The anisotropy of Fe16N2 is small but detectable.

57Fe Mössbauer studies on Si-substituted Er2Fe17

Abstract The compound Er 2 Fe 17 crystallizes in the hexagonal Th 2 Ni 17 structure, and is ordered magnetically with a Curie temperature T c of 305 K. We have investigated the effect of substituting small amounts of Si for Fe on the magnetic behavior of this compound by low temperature 57 Fe Mossbauer spectroscopy and magnetization measurements. Fe can be replaced by Si to form Er 2 Fe 17−x Si x alloys with x up to 3.0 without changing the crystal structure, though a small amount of a second phase appears in X = 3.0 sample. The substitution of Si causes a decrease in the average Fe magnetic moment. The lattice parameters decrease upon Si substitution, and T c increase from 305 K for x = 0 to 498 K for x = 3.0. 57 Fe Mossbauer spectroscopy measurements indicates no preferential subtitution of Si among the four crystallographically different Fe sites.

Magnetic properties of LaCo13-based systems

Four polycomponent systems based on LaCo13 have been studied: La(Co1−xFex)13, La(Co1−xAlx)13, La(Co1−x−yFexAly)13, and La0.7Nd0.3(Co0.7Fe0.3)13. These 1:13 systems were studied because of their potential for permanent magnet fabrication. LaCo13 has a high 3d metal content, the highest for any known rare‐earth intermetallic, a 13 kG saturation induction, and a high Tc (1318 K). Unfortunately, it is cubic and lacks anisotropy. The substituted systems were examined as a portion of a program to find LaCo13‐based systems of applications significance. Replacement of Co in LaCo13 by Fe and/or Al leads to a rapid decline in Tc for all systems studied. Replacement of Co by Al results in a decline in moment, whereas replacement by Fe leads to a rise in moment to 2.39μB/3d atom for La(Co0.4Fe0.6)13, as compared to 2.46μB/3d atom for Fe0.7Co0.3. Analysis of the magnetic data shows that vacancies occur in both half‐bands for LaCo13 (4.8 spin up and 3.24 spin down) but in only one half‐band in La(Co1−xAlx)13 for x≥0.2....

Magnetic behavior of R1.9Zr0.1Fe14B and R1.9Zr0.1Fe12Co2B compounds

Abstract Magnetic properties of R1.9Zr0.1Fe14B (R = Y, Ce, Pr, Nd, Gd, Dy) and R1.9Zr0.1Fe12Co2B (R = Pr, Nd) have been determined. The effect of substitution of R by Zr on the saturation magnetization, Curie temperature and anisotropy is presented. All the compounds show a decrease in magnetic moment and Curie temperature but an increase in anisotropy field. For example, in Nd1.9Zr0.1Fe12Co2B, μs = 32.1μB, Tc = 715 K and HA = 83 kOe.

Enhanced Fe moment in nitrogen martensite and Fe16N2 (invited)

Nitrogen martensite was prepared by treating fine Fe powder with NH3/H2 gas mixtures at temperatures around 665 °C. Upon quenching to a temperature Tq, the γ phase which had formed at the elevated temperature undergoes a martensitic transformation to form nitrogen martinsite (α’ Fe‐N alloy), a tetragonal material. Heat treating this material for 1–2 h at 140±10 °C produced the α‘ phase Fe16N2. The α’ phase occurred along with γ Fe‐N. From x‐ray line intensities, the amount of α’ phase was ascertained. The α’ phase exhibits a room‐temperature moment of 250±10 emu/g. Fe16N2 is formed along with α Fe and also there is retained N‐austenite. Using XRD and conventional magnetic measurement procedures, one obtained 280±10 emu/g for the saturation moment of Fe16N2. The experimental Fe moment, 2.88 μB, is in excellent agreement with the most recent band‐structure calculations, 2.85 μB. The ternary systems (Fe,M)16N2 were studied with M=Mn or Ni. γ Fe‐Mn nitride readily forms, but it does not undergo the γ→α’ trans...