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Nanocrystalline two-phase Nd9Fe85.5Nb1.0B4.5-yCy magnets (y=0.5-4.5) have been prepared by melt spinning and subsequent heal treatment. The effect of remanence enhancement has been observed in the melt-spun ribbons after a proper annealing procedure. A two-phase nanocomposite Nd9Fe85.5Nb1.0B4.0C0.5 magnet with optimum magnetic properties of H-cj.=6.6 kOe, J(r)=10.22 kGs and (BH)(max)=13.32 MGOe has been obtained. (C) 2001 Elsevier Science B.V. All rights reserved.

In the present paper, based on the investigation of the structure and magnetic properties of the compounds RFe11.35Nb0.65Cy (R=Y, Tb, Dy, Ho, Er) and YxDy1−xFe11.35Nb0.65Cy (x=0,0.4,0.6,0.8,1.0) and their parent compounds, a study of the effect of the volume change due to carbonation on the Curie temperature of these compounds has been performed. The d ln TC/d ln V values were derived by comparing the Curie temperature and volume before and after carbonation. Our results indicate that the relationship between d ln TC/d ln V and the Curie temperature TC can be well described in terms of the itinerant-model formalism.

The magnetocrystalline anisotropy and the spin reorientation of Sm1−xDyxFe10.5Mo1.5 were investigated in detail. At room temperature, all Sm1−xDyxFe10.5Mo1.5 alloys possess easy c-axis anisotropy and the magnetocrystalline anisotropy field decreases with increasing Dy concentration. However, at low temperature, a spin reorientation transition of axis-to-cone type was observed in the Sm1−xDyxFe10.5Mo1.5 alloys with x ≥ 0.8. The spin reorientation temperatures increase with increasing Dy concentration in the Sm1−xDyxFe10.5Mo1.5 alloys.

Interstitial rare-earth iron-rich Sm 3 (Fe,Cr) 29 X y (X=N, C) compounds with the monoclinic Nd 3 (Fe,Ti) 29 structure have been successfully synthesized by gas–solid reaction. An intrinsic coercivity μ 0i H c of ∼0.80 T at 293 K has been attained for both the nitride and carbide prepared by ball-milling. The intrinsic coercivity μ 0i H c of the nitride powder increases with decreasing average particle size d and exhibits a maximum at d =0.4 μm, then decreases slowly for smaller d values. Our results suggest that the coercivity of the Sm 3 Fe 24 Cr 5 N y powder is mainly controlled by a nucleation mechanism as observed in the Sm 3 (Fe,Ti) 29 N y and 2:17:N nitrides. A remanence of B r =O.87 T has been achieved at 293 K for Sm 3 Fe 24 Cr 5 N y which gives an energy product of (BH) max =l04.8 kJ/m 3 . Similar hard magnetic properties were observed for the carbide powder. The temperature coefficient of the remanence of the carbide is worse than that of Nd–Fe–B, although it has a better temperature coefficient of coercivity. Both the nitride and carbide powders have better corrosion resistance than commercial Nd–Fe–B powder.

The variation in crystal structure and intrinsic magnetic properties with Y concentration has been investigated for the Dy 1− x Y x Fe 11 Mo system in detail. The lattice parameters a , c of Dy 1− x Y x Fe 11 Mo slightly increase while the Curie temperatures decrease with increasing Y concentration. At room temperature, all Dy 1− x Y x Fe 11 Mo samples exhibit a uniaxial magnetocrystalline anisotropy. The anisotropy field is enhanced slightly by increasing the Y concentration at room temperature. A spin reorientation transition was observed at low temperature for the Dy 1− x Y x Fe 11 Mo samples with x =0–0.8, and the spin reorientation temperature decreases with increasing of Y concentration.

In the present paper, a study of the effect of the volume change on the Curie temperature ( T C ) of R(Fe,M) 12 (M=Nb, Ti and V) due to nitrogenation has been performed. The dln T C /dln V values were derived by comparing the Curie temperatures and volumes before and after nitrogen. Our results indicate that the relationship between dln T C /dln V and the Curie temperature T C agrees with an itinerant-model formalism. The effects of volume expansion and the increasing electron correlation play important roles in the enhancement of the Curie temperature upon nitrogenation of intermetallic compounds.

The novel ternary rare-earth iron-rich interstitial compounds R 3 (Fe,Cr) 29 X y (R=Nd, Sm and X=N, C) with the monoclinic Nd 3 (Fe,Ti) 29 structure have been successfully synthesized. Introduction of the interstitial nitrogen and carbon atoms led to a relative volume expansion ΔV / V of about 6% and an enhancement of Curie temperatures T c about 268 K for the nitride and about 139 K for the carbide, respectively. The Nd 3 Fe 24.5 Cr 4.5 X y compounds have a planar anisotropy at room temperature. A first-order magnetization process (FOMP) with critical field B cr =4.4 T and 3.1 T at room temperature were observed for the Nd-nitride and carbide compounds, respectively. The Sm 3 Fe 24 Cr 5 X y compounds were found to have a large uniaxial anisotropy of about 18 T at 4.2 K and about 11 T at 293 K. A FOMP with B cr =2.3 T was also observed in the Sm-nitride compounds at 4.2 K. Magnets with coercivity of μ Oj H c ∼0.8 T at 293 K has been successfully developed from the Sm 3 Fe 24 Cr 5 X y (XN and C) phases.

Room-temperature 57Fe Mossbauer spectra have been measured in Sm2Fe17 under different heat treatment conditions. The details of fitting these spectra is exhaustively discussed. The spectra of Sm2Fe17 are split into seven inequivalent magnetic sites. An identical result was obtained by using two fitting modes. The following has been indicated from the results for all samples. Firstly for these samples containing α-Fe sextets and paramagnetic doublets, by choosing an appropriate annealing system, the smallest amount of impurities might be obtained, i.e. an approximately single-phase Sm2Fe17 compound was obtained. Secondly the overall weighted average fields were all approximately equal. This was thought to arise because the different heat treatment conditions caused no change in the near-neighbour coordination of iron atoms. Thirdly the 6c site and 18 h site had the largest and the smallest hyperfine fields, respectively.

A new series of compounds, Gd x Dy 1− x Fe 11.35 Nb 0.65 , with a ThMn 12 structure was synthesized. The corresponding nitrides prepared by gas solid reaction retain the structure of their parent alloys, but with an expansion of 3% of the unit cell volume. Their Curie temperature increases by about 200 K. For the alloys, the spin-reorientation transition temperature T sr1 decrease, while the Curie temperature and the magnetocrystalline anisotropy field increase with the substitution of Gd for Dy. Upon nitrogenation, the spin reorientation of the nitrides disappear, and the magnetocrystalline anisotropy field of the nitrides decrease with increasing Gd content.

The X-ray diffraction pattern of the novel Sm 3 (Fe 0.933 Ti 0.067 ) 29 compound was indexed on the basis of monoclinic symmetry with the lattice parameters a = 1.065 nm, b = 0.858 nm, c = 0.972 nm and β = 96.98°. The Sm 3 (Fe 0.933 Ti 0.067 ) 29 compound exhibits ferromagnetic ordering with T C = 486 K and a planar anisotropy. The new interstitial nitride of the Sm 3 (Fe 0.933 Ti 0.067 ) 29 N 5 compound was obtained by gas-solid phase reaction. The nitride has the same structure as the parent compound. The introduction of nitrogen leads to an increase in the Curie temperature to 750 K. The saturation magnetization values σ s = 160 A m 2 kg −1 at 4.2 K and 140 A m 2 kg −1 at 293 K. The anisotropy was changed from planar to uniaxial upon nitrogenation. The anisotropy field B a values were 18.1 T at 4.2 K and 12.8 T at 293 K. The hard magnetic properties of the Sm 3 (Fe 0.933 Ti 0.066 ) 29 N 5 compound have been studied. A coercivity μ 0i H c value of 0.83 T and a maximum energy product ( BH ) max of 105 kJ m −3 at 293 K have been achieved. The Sm 3 (Fe 0.933 Ti 0.067 ) 29 Ny compound is a promising material for permanent magnetic applications.

In the present paper the diffusion behavior of nitrogen in Sm 2 Fe 17 has been investigated. The Curie temperatures of nitrides are experimentally found to vary in a very narrow temperature range. No other intermediate nitride with a small Curie temperature has been found. After the further annealing of non-fully nitrided powder in an Ar atmosphere, some of the nitrogen atoms, which have weak interactions with the interstitial site, can be excited from interstitial sites of Sm 2 Fe 17 molecule by thermal energy and migrate again. However, some of nitrogen atoms are still located at interstitial sites of Sm 2 Fe 17 molecule owing to the strong interaction between gas atoms and the interstitial site. In the nitrogen diffusion process, with increasing occupation of the interstitial site in Sm 2 Fe 17 by nitrogen atoms, the diffuse force for nitrogen atom decreases owing to the change in the chemical potential of system, which results in different diffusive activities of nitrogen atoms under different nitrogen absorption contents x in Sm 2 Fe 17 N x . Meanwhile the particle size dependence of the diffusion behavior has also been discussed. The surface and the grain boundary diffusion modes play important roles in the diffusion process of nitrogen atoms into Sm 2 Fe 17 particles especially for small particles.

Two new compounds of the type RFe 11.4 Nb 0.6 (R = Y, Gd) with ThMn 12 structure were synthesized. The corresponding nitrides retain the same structure as their parent alloys, but with an expansion in the unit cell volume of about 3%. The temperature dependences of saturation magnetization and anisotropy field were determined from 4.2 K to room temperature for the Y compound and its nitride. The Curie temperature is 597 K for GdFe 11.4 Nb 0.6 and 773 K for its nitride. The effect of the third stabilizing element on the Curie temperature of ThMn 12 -type ternary rare-earth iron-rich compounds was investigated and discussed in terms of a diagonal positional relationship in the periodic table of the elements.

Nd 1+ x Fe 10 Mo 2 N y nitrides with permanent magnetic properties were prepared by heating fine Nd Fe Mo particles in an N 2 atmosphere followed by milling. The best composition and nitriding and milling conditions to obtain a high coercivity and energy product for the nitrides were investigated. H c and B r of magnetically aligned samples increased and decreased monotonically respectively with increasing milling time after nitriding irrespective of composition and nitriding conditions. The room temperature properties μ o H c = 0.7 T, B r = 0.4 T and ( BH ) max = 42 kJ m −3 were obtained.

Sintered magnets of Sm2Fe17Ny nitrides, with a density of 6.0–7.4 g/cm3, have been prepared by using an explosion technique. Both crystalline structure and the magnetic properties of Sm2Fe17Ny nitrides were retained in the process. The sintered magnet had a remanence Br=0.83 T, an intrinsic coercivity μ0iHc=0.57 T and an energy product (BH)max=88 kJ/m3. The temperature dependence of coercivity and remanence were also measured. The temperature coefficients α of remanence and β of coercivity are −0.076%/°C and −0.51%/°C, respectively.

The Sm2Fe17Ny nitrides with nitrogen concentration y = 2 to 8 have been prepared using a mixed gas atmosphere of NH3 and H-2. Their intrinsic magnetic properties were studied at 1.5 and 293 K. The Th2Zn17-type structure is maintained when y is less than 6. The 9e sites can be fully occupied and the 18g sites may be half occupied by nitrogen atoms. The nitrogen at the 9e sites and 18g sites have a positive effect and a negative effect, respectively, on the intrinsic magnetic properties of Sm2Fe17 compound. The nitride Sm2Fe17N3 has the best intrinsic magnetic properties.

In the present paper, a study of the effect of the volume change on the Curie temperature of R–Fe–N and R–Fe–Ti–N compounds with TbCu 7 structure has been performed. Our results indicate that the relationship between dln T C /dln V and the Curie temperature T C in rare earth –iron based nitrides with TbCu 7 structure can be well described in terms of the itinerant-electron model formalism.

In the present work, the phenomenon of simultaneous enhancement of remanence and coercivity for Nd–Fe–B/Nb magnets prepared by sintering of mixed Nd–Fe–B and Nb powders is reported and its mechanism is investigated. The appropriate addition of Nb powder may suppress the appearance of Nd-rich phases at Nd 2 Fe 14 B grain boundaries and the excess Nd-rich composition may become available to form more of the Nd 2 Fe 14 B phase, which is responsible for the enhancement of the remanence. The reversal of hard Nd 2 Fe 14 B grains was suppressed by a decreasing amount of α-Fe, by better decoupling between the magnetic grains due to formation of the Nb-rich phase or by pinning of domains at the Nb-rich phase.

The melt spun ribbons of two-phase nanocomposite Nd2xFe 95-2xCo4Nb1Bx(x = 4-6) have been prepared by rapid quenching and post heat treatment. The effect of exchange coupling between the nanostructure grains of Nd2(Fe, Co, Nb)14B and α-Fe(Co, Nb) are observed clearly. The sample with x = 4 has both the highest Curie temperature enhancement (about 10 K) and the largest remanence enhancement. The sample with x = 6 has the highest coercivity (about 1.31 T). The best magnetic properties obtained in Nd9Fe81.5Co4Nb1B4.5 ribbons are as follows: (BH)max=154.4 kJ/m3, Jr= 1.11 T and μ0Hcj=0.65 T.

The iron rich intermetallic compound Y/sub x/Dy/sub 1-x/Fe/sub 11.35/Nb/sub 0.65/ (x=0, 0.2, 0.4, 0.6, 0.8, 1.0) and their carbides Y/sub x/Dy/sub 1-x/Fe/sub 11.35/Nb/sub 0.65/C have been investigated. By the substitution of Y for Dy, for the alloys, the spin reorientation transition temperature (T/sub sr1/) decreases, and the saturation magnetization M/sub s/ and the anisotropy field B/sub a/ increase. The carbide Y/sub x/Dy/sub 1-x/Fe/sub 11.35/Nb/sub 0.65/C has a T/sub c/ around 710 K, M/sub s/ in the range 90/spl sim/140 JT-/sup 1/kg/sup -1/ and /spl mu//sub 0/H/sub a/, changing rapidly with Y content at room temperature.

Magnetization curves have been measured on both epoxy resin-fixed random and magnetically aligned powder samples of Y/sub 3/(Fe/sub 27.4/Ti/sub 1.6/) at temperatures of 1.5, 100, 200 and 293 K with an applied magnetic field up to 7 T. The X-ray diffraction pattern of the Y/sub 3/(Fe/sub 27.4/Ti/sub 1.6/) sample suggests a planar easy magnetization direction underlying hexagonal CaCu/sub 5/ structure. The room temperature anisotropy field deduced from these magnetization data is 3.0(5) T and reaches 7.3(5) T at 1.5 K. The average Fe magnetic moment at 7.0 T is 1.44(1) /spl mu//sub B/ at 293 K and 1.86(1) /spl mu//sub B/ at 1.5 K, respectively.

Sm/sub 2/Fe/sub 17/ carbides were prepared by arc-melting and gas-solid reaction (GSR). Zn-bonding was investigated as a means of developing coercivity on these carbides. Positive results, were found by Zn-bonding carbides prepared by GSR where coercivities up to 0.9 T could be achieved after a proper heat-treatment. The /spl alpha/-Fe originated due to disproportionation seems to be one primary hindrance for achieving coercivity values as high as for Zn-bonded nitrides. The effect of heat treatment conditions and Zn-content on the development of coercivity in Sm/sub 2/Fe/sub 17/ carbides is discussed and compared to results on nitrides. >

The hard magnetic properties of NdFe/sub 12-x/Mo/sub x/N/sub 0.9/ with low Mo concentration (x=1.25 and 1.5) have been studied. The coercivity varies with the ball milling time and reaches a maximum at about 800 minutes. Coercivity values /spl mu//sub 0J/H/sub c/ of 0.64 T and 0.55 T have been achieved for nitrides with x=1.25 and 1.5, respectively. The oxygen content of ball milled nitrides is less than 1 wt%. Metal bonding of NdFe/sub 12-x/Mo/sub x/No/sub 0.9/ with Zn has less effect on coercivity than for Sm/sub 2/Fe/sub 17/N/sub y/. >

New members of ThMn/sub 12/-structure family RFe/sub 11.35/Nb/sub 0.65/ (R=Y, Dy, Er) have been synthesized and studied by x-ray diffraction, ac susceptibility measurements and thermomagnetic analysis. Spin reorientation transitions were observed in DyFe/sub 11.35/Nb/sub 0.65/ and ErFe/sub 11.35/Nb/sub 0.65/ compounds. The transition temperatures of spin reorientation were determined to be T/sub sr1/=160 K and T/sub sr2/=235 K for DyFe/sub 11.35/Nb/sub 0.65/, and T/sub sr/=41 K for ErFe/sub 11.35/Nb/sub 0.65/, respectively. The spin reorientation transitions are quenched by nitrogenation. >

The substitution of elements M (M=Nb, V, Ti, Co) for Fe in Sm/sub 2/Fe/sub 17/N/sub y/ is investigated regarding its structural and magnetic properties. Zn-bonding as well as milling of Sm/sub 2/(Fe/sub 1-x/M/sub x/)/sub 17/N/sub y/ is studied as a means of improving the properties of their corresponding permanent magnets. Co-substitution improves the temperature dependence of remanence while V-containing magnets show a better shape of the demagnetization curve. Additional milling of nitrides enhances the coercivity, due to pinning of domain walls or to single domain particle behavior. Zn bonding of very fine Sm/sub 2/Fe/sub 17/N/sub y/ powders, followed by heat treatment, e.g., 425 degrees C for 100 min, leads to an overall decrease of the permanent-magnet properties caused by the formation of alpha -Fe. >

In a systematic study of the ternary iron-rich rare earth alloys GdFe12−xGex (3.6 < x < 8.0), a new ternary iron-rich rare earth intermetallic compound of the approximate composition GdFe8.4Ge3.6 has been synthesized. The Curie temperature of the compound GdFe8.4Ge3.6 is about 928 K. The lattice symmetry of the compound is tetragonal. The light rare earth compound SmFe8.4Ge3.6 was also prepared, and its lattice parameters and Curie temperature are reported.

The formation, structure and magnetic properties of (Er1-xYx)(2)Fe17C2 (0 less than or equal to x less than or equal to 1.0) prepared by melt spinning were studied. Arc-melted (Er1-xYx)(2)Fe17C2 alloys are found to have a two-phase structure with the 2:17 phase and a predominant alpha-Fe phase. Melt spinning (ER(1-x)Y(x))(2)Fe17C2 results in the crystallization of the Th2Zn17-type structure at appropriate quenching rates of v(s)=10-20 m s(-1). X-ray diffraction and thermomagnetic measurements show that they are of single phase. The substitution of Y for Er was found to have a small influence on the unit-cell volume v and Curie temperature T-c. The saturation magnetization sigma(s) is enhanced from 77.4 to 169.0 emu g(-1), as x increases from 0 to 1.0, but the Fe magnetic moment is approximately constant. Spin reorientation transitions are observed in the samples with x less than or equal to 0.8. The substitution of Y decreases the uniaxial anisotropy of the Er sublattice, resulting in a monotonic decrease in spin reorientation temperature from 137 K for x=0 to 44 K for x=0.8.