The outstanding permanent magnetic material Nd2Fe14B possesses very high energy product. But its Curie temperature is a little bit too low for practical application. Some elements were added into the material in order to raise the Curie temperature. Reference [9] and our recent experimental results show that the Curie temperature can be made higher by partiy subsituting silicon for iron in the material and in Y2Fe14B. For understanding the effect of silicon on magnetism, the occupancy of Si in Y2Fe14B was studied by neutron diffraction. The neutron diffraction results show that silicon occupies preferentially the sites of c, j1, and k2. The magnetic interaction theory is applied to explain the experimental results.

YTi(Fe 1-x Co x ) 11 crystallizes in the ThMn 12 -type tetragonal structure, with x ranging from 0.0 to 1.0, the Curie temperature increases with the increase of Co content. In order to understand the relation between magnetic properties and microst-ructure of these compounds, we studied their M?ssbauer spectra. The M?ssbauer effect measurements were carried out at room temperature on YTi(Fe 1-x Co x ) 11 , with x equal to 0.0, 0.2 and 0.4. The best fits confirm that Co atoms preferentially occupy the j and f sites. The hyperfine fields of the measured samples reach a maximum at x = 0.2,which is in agreement with the results of magnetic measurements. By comparing the experimental results of M?ssbauer spectra of YTi(Fe 1-x Co x ) 11 , Y 2 (Fe 1-x Co x ) 14 B and YTi(Fe 1-x Ni x ) 11 , we analyze the difference of the 3d band structure between YTiFe 11 , and Y 2 Fe 14 B.

We have studied the zero-field hyperfine splitting of Tb-159 in ferrimagnetic Tb2Fe17Cx (x = 1, 1.5, 2) using spin-echo NMR at 4.2 K. Distinct spectra arising from the different sites characterized by the numbers of carbon nearest neighbours (NN = 0, 1, 2, 3) are observed. The measured hyperfine parameters u(t) and P-t for all four spectra are given for x = 1.5 and 2. Analysis of the quadrupolar splitting indicates that in Tb2Fe17C1.5 the dominant contribution to the magnetocrystalline anisotropy arises from the NN = 3 sites.

A systematic investigation of the structure and magnetic properties of arc-melted and as-quenched Sm2Fe17−xGaxC1.5 samples with 0 ≤ × ≤ 6 has been made by X-ray diffraction and magnetic measurements, X-ray diffraction studies have shown that these samples crystallize in the rhombohedral Th2Zn17-type structure. The unit-cell volumes υ of Sm2Fe17−xGaxC1.5 compounds increase monotonically with increasing Ga concentration. The Ga-concentration dependence of the Curie temperature TC exhibits a maximum value of 633 K at about x = 2. The room-temperature saturation magnetization Ms decreases monotonically with increasing Ga concentration. The Sm2Fe17−xGaxC1.5 compounds exhibit an easy c-axis anisotropy at room temperature. The anisotropy field is found first to increase and then to decrease with increasing x, having a maximum value of 130 kOe at about x = 2. The coercivities of 13.0–16.0 kOe are obtained in as-quenched Sm2Fe17-xGaxC1.5 (x = 2 and 3) ribbons prepared at the speeds of 15–30 m/s at room temperature. The substitution of Ga in Sm2Fe17C1.5 not only stabilizes the hard magnetic phase but also leads to the increase in coercivity.

The formation, structure and magnetic properties of (Er1 − xYx)2Fe17C2 (0 ⩽ x ⩽ 1.0) prepared by melt spinning were studied. Arc-melted (Er1 − xYx)2Fe17C2 alloys are found to have a two-phase structure with the 2:17 phase and a predominant α-Fe phase. Melt spinning (Er1 − xYx)2Fe17C2 results in the crystallization of the Th2Zn17-type structure at appropriate quenching rates of vs = 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 Tc. The saturation magnetization σs 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 ⩽ 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.

The structure and magnetic properties of Sm2Fe17−xGaxC2.5 (x = 2, 3, 4 and 5) compounds prepared by arc-melting were studied. X-ray diffraction shows that these samples are single phase with rhombohedral Th2Zn17-type structure. The unit-cell volumes v of Sm2Fe17−xGaxC2.5 compounds increase monotonically with increasing Ga concentration from 832.7 Å3 for x = 2 to 847.4 Å3 for x = 5. The Curie temperature TC and room temperature saturation magnetization Ms are found to decrease monotonically with increasing Ga concentration. The Sm2Fe17−xGaxC2.5 compounds exhibit an easy c-axis anisotropy at room temperature. The anisotropy field is 135 kOe for x = 2, and decreases to 76 kOe at x = 4. A room temperature coercivity exceeding 13 kOe is obtained in as-quenched Sm2Fe17−xGaxC2.5 ribbons with x = 2 and x = 3.

We have studied the structure and magnetic properties of Er2Fe17−xGaxC2 (x = 0, 1, 2, 3, 4, 5 and 6) compounds by means of X-ray diffraction and magnetic measurements. Crystal structure studies have shown that these carbides have a rhombohedral Th2Zn17-type structure. The lattice constants and the unit cell volumes increase linearly with increasing Ga concentration x. The Curie temperature of Er2Fe17−xGaxC2 with x ≤ 2 is almost independent of Ga concentration, having a TC higher than 600 K, and then decreases rapidly with increasing Ga concentration. An monotonic decrease of the saturation magnetization with x is observed when non-magnetic Ga atom is substituted for Fe. Er2Fe17−xGaxC2 samples with x ≤ 5 exhibit a spin reorientation transition. The spin reorientation temperature Tsr is found first to increase, goes through a maximum value of 227 K at about x = 2, and then decreases monotonically with increasing Ga concentration.

The carbides (Er1−xSmx)2Fe17Cy (0≤x≤0.8) with a carbon concentration up to y=3.0 for the Er-rich region and up to y=1.5 for the Sm-rich region have been successfully prepared by melt spinning. They are found to crystallize in the hexagonal Th2Ni17-type or the rhombohedral Th2Zn17-type structure and to be stable at high temperature. The introduction of the interstitial carbon results in a large increase in the unit-cell volumes and Curie temperatures. The room-temperature saturation magnetization is found to increase with increasing carbon or samarium concentrations. X-ray diffraction studies of magnetically aligned powder show that the samples with x<0.2 or y≤0.5 exhibit easy plane anisotropy while the samples with x≥0.2 and y≥1.0 exhibit easy c-axis anisotropy at room temperature. For (Er0.2Sm0.8)2Fe17C1.5, the room-temperature anisotropy field is found to be 8 T, which is comparable to that of Nd2Fe14B.

The compounds were prepared by arc-melting. It was found that (1) the Sm 2Fe 17-xGa xC 1.5(3��x��6) carbides crystallize in the rhombohedral Th 2Zn 17-type structure and the single-phase compound of Sm 2Fe 17-xSi xC 1.5 can only be obtained as x is 2; (2) the Curie temperature of Sm 2Fe 17-xGa xC 1.5 compounds decreases monotonically with increasing the Ga concentration x from 633K for x=2 to 351K for x=6; (3) the T c of Sm 2Fe 15Si 2C 1.5 compounds is 578K; (4) all compounds studied in this paper exhibit an easy C-axis anisotropy at room temperature; (5) the anisotropy field of Sm 2Fe 14Ga 3C 1.5 and Sm 2Fe 15Si 2C 1.5 compounds is founds to be 90 and 115 kOe respectively. (6) a room-temperature coercivity of 16 kOe is obtained in rapidly quenched Sm 2Fe 15Ga 2C 1.5 alloy prepared at a speed of 25m/s.

The single-phase compounds of Gd2Fe17−xGaxC2 (x=0, 1, 2, 3, 4, 5, and 6) with rhombohedral Th2Zn17-type structure were prepared by melt spinning for x≤1 and arc melting for x≥2. Their formation, structure, and magnetic properties were studied. The substitution of Ga for Fe in Gd2Fe17C2 helps the formation of the 2:17-type structure. The addition of Ga results in the increase of the lattice constants and the unit-cell volumes. The Curie temperature has a small change when x≤2, and then decreases rapidly with increasing Ga concentration. An approximately linear decrease of the saturation magnetization with x is observed when the nonmagnetic Ga atom is substituted for Fe.

The crystallographic and magnetic structures of Ho2Fe17-xGaxC2 (x=4.0 and 5.5) at room temperature were refined by the Rietveld analysis of neutron powder diffraction data. The analysis indicates that Ho2Fe17-xGaxC2 has a Th2Zn17-type structure space group, (R3m); the gallium atoms occupy only 18h sites with an occupancy of 0.66 for x=4.0, they occupy both 18h and 6c sites with occupancies of 0.66 and 0.75, respectively, for x=5.5 and they are absent from the 9d and 18f sites at all gallium concentrations. The carbon atoms occupy 9e sites. For the x=4.0 compound, the magnetic moments of all atoms lie in a plane perpendicular to the sixfold axes and have a parallel arrangement. The magnetic moments of all Fe atoms display ferromagnetic coupling, but the magnetic moments of Ho and Fe are antiferromagnetically oriented. The x=5.5 compound is paramagnetic at room temperature.

The magnetic hardening of the Sm2Fe14Ga3Cx was investigated by melt spinning. It was found that high coercivities can be achieved by direct quenching at the optimum substrate velocity. The coercivities of 12.6–15.0 kOe were obtained in Sm2Fe14Ga3Cx ribbons with carbon contents x from 1.0 to 2.5. The as-quenched Sm2Fe14Ga3C1.5 ribbons had a coercivity exceeding 13 kOe within a large range of quench rates between 18 and 30 m/s. X-ray diffraction experiments indicate that the ribbons are almost entirely comprised of the Th2Zn17 phase. It is concluded that Ga not only stabilizes the hard magnetic phase but also is very effective in raising the coercivity in the Sm2Fe14Ga3Cx melt-spun ribbons.

Formation, structure and magnetic properties of Ｓｍ2Ｆｅ17-xＭxＣ1.5（Ｍ＝Ｇａ，Ｓｉ） compounds prepared by arc-melting were studied. The Ｓｍ2Ｆｅ17-xGaxＣ1.5(3≤x≤6) carbides crystallize in the rhombohedral Ｔｈ2Ｚｎ17-type structure and the single-phase compund of Ｓｍ2Ｆｅ17-xSixＣ1.5 can only be obtained as x is 2. It is found that the Curie temperature of Ｓｍ2Ｆｅ17-xGaxＣ1.5 compounds decreases monotonically with increasing Ga concentration x from 633K for x=2 to 351K for x=6，and the Tc of Ｓｍ2Ｆｅ15Si2Ｃ1.5 compound is 578K. All compounds studied in this work exhibit an easy c-axis anisotropy at room temperature. The anisotropy field of Ｓｍ2Ｆｅ14Ga3Ｃ1.5 and Ｓｍ2Ｆｅ15Si2Ｃ1.5 compounds is found td be 90 and 115 kOe, respectively. A room-temperature coercivity of 16 kOe is obtained in rapidly quenched Ｓｍ2Ｆｅ15Si2Ｃ1.5 alloy prepared at。speed of 25 m/s.

The formation, structure, and magnetic properties of Tm2Fe17Cx compounds with x=0, 0.5, 1.0, 1.5, 2.0, 2.5, and 2.8 were studied. The samples with x≤1.0 were arc melted and heat treated at 1370 K for 14 h. The carbides were prepared by melt spinning at appropriate quenching rates of vs=10–20 m/s for 1.5≤x≤2.5 and by the crystallization from corresponding amorphous for x=2.8. X-ray diffraction and thermomagnetic measurements show that all samples studied are single phase with the hexagonal Th2Ni17-type structure except for Tm2Fe17C2.8, which contains a few percent of α-Fe. The lattice parameters a,c and the unit-cell volumes v increase as the carbon concentration x increases. The Curie temperature is found to rise with x from 260 K for x=0 to 669 K for x=2.8. The saturation magnetization Ms at 1.5 K is found to be 92.2–97.1 emu/g as x varies from 0 to 2.8, and the carbon concentration dependence of the Fe moment is approximately constant (2.12±0.04μB). The spin-reorientation transitions are observed. The spin-reorientation temperature is found to increase with the carbon concentration for x≤1.5, and then has a slight decrease with x for x≳1.5.

The alloys Y2(Fe0.8Ga0.2)17Cx (x=0–2.5) with the rhombohedral Th2Zn17 phase were prepared by arc melting. The lattice parameters and the unit-cell volumes derived from x-ray-diffraction measurements increase linearly with the carbon content x. The Curie temperature Tc increases at first with increasing carbon concentration x, shows a maximum value of 558 K at about x=1.0, then decreases with x. The saturation magnetization at 1.5 K and the Fe magnetic moment have a slight change with the interstitial carbon content. The dilution of Fe by nonmagnetic Ga decreases the saturation magnetization and the Fe magnetic moment.