Bo-Ping Hu

Achievement of high coercivity in sintered R-Fe-B magnets based on misch-metal by dual alloy method

The R-Fe-B (R, rare earth) sintered magnets prepared with different ratio of alloys of MM-Fe-B (MM, misch-metal) and Nd-Fe-B by dual alloy method were investigated. As expected, the high ratio of MM-Fe-B alloy degrades the hard magnetic properties heavily with intrinsic coercivity lower than 5 kOe. When the atomic ratio MM/R ≤ 21.5% the magnetic properties can reach a practical level of Br ≥ 12.1 kGs, Hcj ≥ 10.7 kOe, and (BH)max ≥ 34.0 MGOe. And the effect of Hcj enhancement by the grain boundary diffusion process is obvious when MM/R ≤ 21.5%. It is revealed that the decrement of intrinsic magnetic properties of R2Fe14B matrix phase is not the main reason of the degradation of the magnets with high MM ratio. The change of deteriorated microstructure together with phase component plays fundamental roles in low Hcj. In high MM ratio magnets, (a) after annealing, Ce atoms inside main phase are inclined to be segregated in the outer layer of the main phase grains; (b) there is no thin layer of Ce-rich phase a...

Magnetic properties of a novel Sm3(Fe, Ti)29 phase

Abstract In a systematic study of the Sm 10 Fe 85 Ti x (4.7 x 3 (Fe, Ti) 29 compound has been found to be a new phase, of which the structure is Nd 3 (Fe, Ti) 29 -type. The X-ray diffraction pattern of Sm 3 (Fe 0.933Ti 0.06 7) 29 can be indexed on the 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 a Curie temperature T C = 486 K. The saturation magnetization M S is 125 A m 2 /kg at 77 K and 119 A m 2 /kg at room temperature. The room temperature anisotropy field is 3.4 T.

MAGNETIC-PROPERTIES OF SM2(FE1-XMX)17NY NITRIDES (M = CO, NI, AL, TI, V)

Abstract The thermal stability, structural and magnetic properties of Sm 2 (Fe 1− x M x ) 17 N y nitrides (M = Co, Ni, Al, Ti and V) have been investigated. The Curie temperature increases with Co concentration but decreases with Ni or Al concentration. The saturation magnetization M s and the anisotropy field B a at room temperature of Sm 2 (Fe 1 - x Co x ) 17 N y both reach their maxima of 147 J/T kg and 15.5 T respectively. All nitrides start to decompose at a similar temperature of ≈ 650°C.

MAGNETIC-PROPERTIES OF A NOVEL SM3(FE, TI)29NY NITRIDE

A new interstitial nitride of Sm3(Fe0.933Ti0.067)29Ny (y=5) has been synthesized. Its x‐ray pattern can be indexed in Nd3(Fe,Ti)29‐type monoclinic symmetry with the lattice parameters of a=1.098 nm, b=0.882 nm, c=0.985 nm, and β=97.50°. The Sm3(Fe0.933Ti0.067)29Ny nitride exhibits ferromagnetic ordering with a Curie temperature Tc=750 K. The saturation magnetization Ms is 160 A m2/kg at 4.2 K and 140 A m2/kg at 293 K. The anisotropy field is 18.1 T at 4.2 K and 12.8 T at 293 K. The coercivity of μ0iHc=0.83 T at 293 K on this new nitride has been developed.

Structural and magnetic properties of NdFe12−xMoxN1−δ compounds

A series of nitrides NdFe12−xMoxNi1−δ with x=1–2.5 and δ≤0.2 have been investigated. All nitrides are of the ThMn12 tetragonal structure with the unit cell volumes about 3% larger than their parent alloys. Curie temperatures are enhanced by nitrogenation about 160 K and increase linearly with decreasing content x of Mo. NdFe12−xMox exhibits a weak uniaxial anisotropy with a value of BA less than 0.6 T when x≥1.75. After nitrogenation, all nitrides have a strong uniaxial anisotropy. Values of the anisotropy field BA increase monotonically from 6.35 T for x=2.5 up to 9.5 T for x=1 as decreasing content x of Mo. Saturation magnetizations also increase monotonically with decreasing content x.

Magnetic properties of R3(Fe,Ti)29Cy carbides (R=Nd, Sm)

R3(Fe, Ti)29Cy carbides (R=Nd, Sm) have been synthesized by gas-solid phase reaction. The Curie temperature is enhanced by carbonation, with values of 651 K and 641 K for Nd and Sm carbides respectively. The saturation magnetization of the carbides is slightly lower than that of their parent alloys. The Sm carbide has a large uniaxial anisotropy field, 21 T at 4.2 K and 14 T at 293 K. A coercivity of mu 0iHc=0.3 T at room temperature in the Sm carbide has been developed.

STRUCTURAL AND INTRINSIC MAGNETIC-PROPERTIES OF SM2FE17NY (Y = 2-8)

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.

Formation and magnetic properties of Sm3(Fe,Ti)29Ny compounds

The formation and magnetic properties of a novel intermetallic Sm3(Fe0.933Ti0.067)29 compound and the Sm3(Fe0.933Ti0.067)29Ny (y=5) nitride have been investigated. The x-ray diffraction patterns of the nitride and the parent compound were indexed on the basis of the Nd3(Fe,Ti)29-type structure with monoclinic symmetry. The parent and the nitride exhibit ferromagnetic ordering with a Curie temperature TC of 486 K for the parent and 750 K for the nitride. Introduction of nitrogen led to an increase in saturation magnetization; Ms for the nitride is 160 A m2 kg-1 at 4.2 K and 140 A m2 kg-1 at 293 K. The nitride has a uniaxial anisotropy with an anisotropy field strength Ba for 25 T at 4.2 K and 12.8 T at 293 K. The coercivity mu 0iHc=0.83 T at 293 K for this new nitride has been determined.

Magnetic properties of sintered Sm2Fe17Ny magnets

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.

A hard magnetic property study of a novel Sm3(Fe,Ti)29Ny nitride

The hard magnetic properties of a new interstitial nitride Sm3(Fe0.933Ti0.067)29Ny (y approximately 5) have been investigated by ball milling. The saturation magnetization linearly decreases with ball-milling time. By ball milling, maxima of remanence Br=1.04 T, intrinsic coercivity mu 0iHc=0.83 T and energy product (BH)max=105 W m-3 are achieved at 293 K.