Easy C-axis Research Articles

Structure and magnetic properties of Tm2Fe17−xGax compounds

Crystal-structure studies on Tm2Fe17−xGax (x=0, 1, 2, 3, 4, 5, 6, 7, and 8) compounds have shown that the prepared samples are single phase with the 2:17-type structure. Both the unit-cell volume and the saturation magnetization at 1.5 K decrease linearly with increasing Ga content. The Curie temperature is found to increase with increasing x; it goes through a maximum value of 485 K at about x=3 to lower values and then it rises again. The Tm2Fe17−xGax compounds exhibit a spin–reorientaiton transition at low temperature. X-ray diffraction measurements on magnetically aligned Tm2Fe17−xGax powders show that the compounds with x⩽6 have the easy-plane type of magnetic anisotropy, whereas the compounds with x⋚7 exhibit the easy c-axis type of magnetic anisotropy at room temperature.

Mössbauer study of the magnetic properties of RFe6Sn6 compounds (R=Y, Gd, Tb, Dy, Ho, Er, Tm)

Magnetic properties of RFe6Sn6 compounds (R=Y, Gd, Tb, Dy, Ho, Er, Tm) have been studied by magnetization and Mössbauer spectroscopy. Magnetization curves of isotropic powder samples at room temperature show a linear response up to 1.1 T with a susceptibility of 0.003–0.006 while Mössbauer spectra indicate magnetic order of Fe. These results confirm antiferromagnetic ordering of the compounds below a Néels point of approximately 400 K. The hyperfine fields of Fe at 25 K are ∼22 T, 45% greater than that for the isostructural FeSn although the difference in volume is only 3%. X-ray diffraction and Mössbauer spectra measured on magnetically oriented samples show that strong easy c-axis anisotropy of Fe sublattice dominates the anisotropy of these intermetallic compounds for any of the rare earth elements. A large quadrupole shift (∼0.30 mm/s at room temperature and 0.36 mm/s at 25 K) is consistent with the strong Fe sublattice anisotropy. The first anisotropy constant K1 was estimated to be of order 1.5×106 J/m3.

Preferential cobalt site occupation in some R 3(Co, M) 11B 4 compounds

Structural and magnetocrystalline anisotropy results obtained by X-ray diffraction on random and magnetically aligned powder samples of Y 3Co 11−xM x B 4 with M = Fe or Al, Gd 3Co 11−xNi x B 4 and Er 3Co 11−xAl x B 4 are presented. It is found that compounds with the Ce 3Co 11B 4-type structure are formed for iron or nickel contents of x ≤ 6 and for an aluminium content of x≤3. The diffraction patterns of magnetically aligned powders show that Y 3Co 11−xM x B 4 with M = Fe or Al change from easy c-axis to easy-plane anisotropy for x≤1. In contrast, Gd 3Co 11−xNi x B 4 and Er 3Co 11−xAl x B 4 remain uniaxial in the studied composition ranges. Based on structural and magnetic data and under the assumptions of the model of individual site contribution to anisotropy (ISA), preferential occupations by Fe and Al of the Co(2 c) sites and by Ni of the Co(3 g) sites are inferred.

Magnetic ordering of the heavy-fermion alloy CeCu 5.1Ag 0.9

The thermodynamic and transport properties of single-crystalline CeCu 5.1Ag 0.9 in magnetic fields are investigated. Measurements of the specific heat, magnetocaloric effect, DC magnetization and electrical resistivity yield a magnetic ( B, T) phase diagram with two antiferromagnetic phases for magnetic fields applied parallel to the easy c-axis. The results are compared to those of CeCu 5Au.

STRUCTURAL AND MAGNETIC PROPERTIES OF Gd Fe Co Ga COMPOUNDS WITH 2∶17 TYPE STRUCTURE

The compounds of Gd2（Fe1-xCox）15Ga2(0≤x≤1.0) and Gd2（Fe0.8Co0.2）17-yGay(0≤y≤8) were prepared by arc melting. Their structure and magnetic properties have been studied by means of X ray diffraction and magnetic measurements. Experimental results show that single phase compounds with the 2∶17-type structure were obtained for all samples. It was found that the unit cell volume of Gd2（Fe1-xCox）15Ga2 compounds decreases, while the Curie temperature Tc increases monotonously with increasing Co concentration. The saturation magnetization Ms at 1.5K first increases with increasing x, then decreases, showing a value of maximum at x=0.2. For Gd2（Fe0.8Co0.2）17-yGay,the unit cell volume increases, the Curie temperature and the saturation magnetization at 1.5K decrease monotonously with increasing Ga content. The substitution of Co or Ga for Fe in Gd2Fe17 compounds results in a change of magnetocrystalline anisotropy of Fe or Co sublattice from easy plane to easy c-axis at room temperature. This is likely related to the preferential site occupancy of Ga atom.

Geometrically frustrated magnetic structures of the heavy-fermion compound CePdAl studied by powder neutron diffraction

The heavy-fermion compound CePdAl with ZrNiAl-type crystal structure (hexagonal space group ) was investigated by powder neutron diffraction. The triangular coordination symmetry of magnetic Ce atoms on site 3f gives rise to geometrical frustration. CePdAl orders below with an incommensurate antiferromagnetic propagation vector , and a longitudinal sine-wave (LSW) modulated spin arrangement. Magnetically ordered moments at Ce(1) and Ce(3) coexist with frustrated disordered moments at Ce(2). The experimentally determined magnetic structure is in agreement with group theoretical symmetry analysis considerations, calculated by the program MODY, which confirm that for Ce(2) an ordered magnetic moment parallel to the magnetically easy c-axis is forbidden by symmetry. Further low-temperature experiments give evidence for a second magnetic phase transition in CePdAl between 0.6 and 1.3 K. Magnetic structures of CePdAl are compared with those of the isostructural compound TbNiAl, where a non-zero ordered magnetic moment for the geometrically frustrated Tb(2) atoms is allowed by symmetry.

High-field magnetization and specific heat of TmNi5

High-field magnetization on two single-crystalline samples from different batches of TmNi5 has been measured along the crystallographic a, b and c directions up to 38 T at 1.5 K. A small high-field susceptibility χHF = 6.3 × 10−3μB/T f.u. was observed along the easy c-axis. The magnetization measured along both a- and b-axis shows hysteresis and a magnetic transition between 5 and 15 T. Specific heat has been measured from 1.5 to 160 K. A λ-type peak found at about 3.7 K originates from the magnetic system.

Effects of Ga substitution on the hard magnetic properties of the Sm 2Fe 17C 1.5 compounds

A systematic investigation of the structure and magnetic properties of arc-melted and as-quenched Sm 2Fe 17− x Ga x C 1.5 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 Th 2Zn 17-type structure. The unit-cell volumes υ of Sm 2Fe 17− x Ga x C 1.5 compounds increase monotonically with increasing Ga concentration. The Ga-concentration dependence of the Curie temperature T C exhibits a maximum value of 633 K at about x = 2. The room-temperature saturation magnetization M s decreases monotonically with increasing Ga concentration. The Sm 2Fe 17− x Ga x C 1.5 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 Sm 2Fe 17- x Ga x C 1.5 ( x = 2 and 3) ribbons prepared at the speeds of 15–30 m/s at room temperature. The substitution of Ga in Sm 2Fe 17C 1.5 not only stabilizes the hard magnetic phase but also leads to the increase in coercivity.

Magnetocrystalline anisotropy of (Sm 0.5RE 0.5)Fe 11Ti compounds (RECe, Pr, Nd, Sm, Gd and Tb)

The intrinsic magnetic properties of (Sm 0.5RE 0.5)Fe 11Ti (RECe, Pr, Nd, Sm, Gd, Tb) compounds were studied by thermomagnetic analysis, vibrating sample magnetometry and computer calculations. (Sm 0.5RE 0.5)Fe 11Ti (RECe, Pr, Nd, Sm, Gd, Tb) compounds had tetragonal ThMn 12-type structure and uniaxial magnetocrystalline anisotropy with easy magnetization c-axis. The anisotropy constant K 1 was in the range of 1.75 to 9.2 MJ/m 3 and approximately one order higher than K 2. Among the compounds investigated, SmFe 11Ti had the highest anisotropy0 of K 1 = 9.2 MJ/m 3, K 2 = 0.4 MJ/m 3 and μ 0 H A = 19.8 T. Substitution of any other rare-earth element for Sm decreased the magnetocrystalline anisotropy.

Structure and magnetic properties of (Pr xDy 1− x)Fe 10.5V 1.5 compounds and their nitrides

The structural and magnetic properties of (Pr x Dy 1− x )Fe 10.5V 1.5 compounds ( x = 0−0.8) and their nitrides have been investigated by X-ray diffraction and magnetic measurements. It is found that single-phase V-stabilized (Pr x Dy 1− x )Fe 10.5V 1.5 compounds can be formed in the Pr content range x = 0−0.8. The substitution of Dy for Pr in the compounds results in the decrease in the lattice parameters and saturation magnetization. The easy magnetization direction at room temperature turns from easy c-axis for x = 0.–0.3 to easy plane for x = 0.4−0.8, while the Curie temperatures remain almost unaffected by the substitution of Dy, with T C values of about 590 K. Upon nitrogenation, the Curie temperature is increased to around 820 K, and the saturation magnetization increases by approximately 20%, while the easy magnetization direction lies along c-axis in the temperature range 0 K to T C. At low Dy contents, the (Pr x Dy 1− x )Fe 10.5V 1.5N y compounds have excellent intrinsic magnetic properties favourable for permanent magnet applications.

Mössbauer study of permanent-magnet materials: Sm 2Fe 17− xGa xC y compounds

Fe 57 Mössbauer spectra of Sm 2Fe 17− x Ga x C y , where 0 ≤ x ≤ 3 and 0 ≤ y ≤ 2.5, have been measured at room temperature and analyzed. These compounds have the rhombohedral Th 2Zn 17 structure. Mössbauer studies indicate that all the samples studied are ferromagnetically ordered. The average hyperfine field for compounds with y = 0 was found to increase for x = 1 and then decrease with increasing x. For fixed x, the average hyperfine field was found to decrease by a very small amount with increasing carbon concentration. Analyses of the spectra show that Ga atoms occupy the 6c, 18h, and 18f but not 9d Fe sites and the fraction of occupancy of Ga is found to depend on x, in agreement with our previous observations on Sm 2Fe 17- x Al x . Some of the compounds studied have an easy c-axis anisotropy and relatively high Curie temperature. The excellent intrinsic magnetic properties make some of these compounds promising candidates for permanent magnet development.

Effect of Co substitution on the magnetic properties of Sm2Fe16SiC compounds

The structural and magnetic properties of compounds in the series Sm-2(Fe1-xCox)(16)SiC are investigated by means of X-ray diffraction (XRD) and magnetization measurements. Samples with x = 0 to 0.3 are prepared by the are-melting method. XRD patterns indicate that are-melted Sm-2(Fe1-xCox)(16)SiC alloys crystallize in the rhombohedral Th2Zn17-type structure. The substitution of Co leads to a decrease in the lattice constants and the unit-cell volume. The Curie temperature increases monotonically with increasing Co concentration from 576 K for x = 0 to 796 K for x = 0.3. The saturation magnetization is higher than 125 emu/g for Sm-2(Fe1-xCox)(16)SiC with x > 0. Sm-2(Fe1-xCox)(16)SiC with x less than or equal to 0.3 compounds exhibit an easy c-axis anisotropy at room temperature and the anisotropy field H-a is found to have a maximum value of 120 kOe for x = 0.1.

Magnetic anisotropy of Dy 2Fe 17− xGa x compounds

The single-phase compounds of Dy 2Fe 17− x Ga x ( x = 0, 1, 2, 3, 4, 5, 6, 7 and 8) were prepared by arc melting. The substitution of Ga in the Dy 2Fe 17 compound is found to have an important effect on their structure and magnetic properties. Dy 2Fe 17 sample has the hexagonal Th 2Ni 17-type structure and the Ga-substituted samples crystallize in the rhombohedral Th 2Zn 17-type structure. The unit cell volumes increase linearly with increasing gallium concentration. The Curie temperature is found first to increase and then to decrease with increasing gallium content x, attaining a maximum value of 557 K at about x = 3, which is 187 K higher than that of Dy 2Fe 17. The saturation magnetization decreases linearly with increasing gallium content from 15.13 μ B /f.u. for x = 0 to −4.27 μ B /f.u. for x = 8. For x ≈ 6, the Fe sublattice moment is found to be about equal to the Dy sublattice moment. X-ray diffraction measurements on magnetically aligned powder samples reveal a change in easy magnetization direction, and the samples with x ≤ 5 exhibit easy plane anisotropy while the samples with x ≥ 6 exhibit easy c-axis anisotropy at room temperature.

Structure and magnetic properties of arc-melted R 2Fe 16SiC x (x = 0∼2.0) compounds with R = Gd, Y and Sm

The structural and magnetic properties of compounds in the series R 2Fe 16SiC x (R=Gd, Y and Sm) have been investigated by X-ray diffraction (XRD) and magnetization measurements. Samples with x= 0, 0.5, 1.0, 1.5 and 2.0 were prepared by arc-melting. XRD patterns indicate that R 2Fe 16SiC x are single phase with the hexagonal Th 2Ni 17-type or the rhombohedral Th 2Zn 17-type structure except for Sm 2Fe 16SiC 2.0, which contains a small amount of α-Fe as a secondary phase. Both the Curie temperature T c and unit cell volume v are found to increase monotonically with increasing C concentration x. The saturation magnetization is almost independent of C content. Samples of Sm 2Fe 16SiC x with x≥0.5 exhibit an easy c-axis anisotropy at room temperature. The anisotropy field H A increases with increasing x from 65 kOe for x=0.5 to about 110 kOe for x=1.5. The Si substitution in the 2:17-type carbides is found to not only help the formation of single phase, but also enhance the anisotropy of the Sm sublattice.

Magnetic hardening of Sm 2Fe 17− xGa xC 2.5 compounds

The structure and magnetic properties of Sm 2Fe 17− x Ga x C 2.5 ( 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 Th 2Zn 17-type structure. The unit-cell volumes v of Sm 2Fe 17− x Ga x C 2.5 compounds increase monotonically with increasing Ga concentration from 832.7 Å 3 for x = 2 to 847.4 A ̊ 3 for x = 5 . The Curie temperature T C and room temperature saturation magnetization M s are found to decrease monotonically with increasing Ga concentration. The Sm 2Fe 17− x Ga x C 2.5 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 Sm 2Fe 17− x Ga x C 2.5 ribbons with x = 2 and x = 3.

Magnetic properties of Sm 2Fe 15Si 2C x compounds prepared by arc melting

X-ray diffraction measurements show that the Sm 2Fe 15Si 2C x ( x = 0, 0.5, 1.0 and 1.5) samples prepared by arc-melting are single phase with the rhombohedral Th 2Z 17-type structure. The unit cell volume v and Curie temperature T c of the Sm 2Fe 15Si 2C x compounds increase monotonically with increasing carbon concentration. The room-temperature saturation magnetization M s is 112.2 emu g −1 for x = 0.5 and it decreases slightly with increasing carbon concentration to 105.6 emu g −1 for x = 1.5. The sample with x = 0 has an easy-plane anisotropy and the samples with x≥0.5 exhibit an easy c-axis anisotropy. The anisotropy field H A at 1.5 K and room temperature increases with increasing carbon concentration from 110 to 195 kOe and from 55 to 105 kOe, respectively, as x increases from x = 0.5 to 1.5.

Non-trivial magnetic order in URu2Si2?

We have searched for the hidden multispin order parameters that have been proposed to explain the weak ordered moment observed in the heavy-fermion superconductor URu2Si2. Since the exotic spin order is predicted to cause broken-symmetry Bragg peaks that develop rapidly with applied magnetic field, we have measured their strength in fields up to 8 T, for which a large easily observable moment is predicted. The Bragg neutron scattering is found to decrease rather than increase when a field is applied along the easy tetragonal c-axis, while there is no change for a field at right angles. The results rule out the proposed symmetric multispin order parameters. The zero-field transition is found to exhibit critical softening of the spin gap and a cusp in the susceptibility at TN, as expected for the ordering of magnetic dipoles.

Structural and magnetic properties of R2Fe17-xAlxC compounds (R identical to Ho, Y or Sm)

The single-phase compounds of R2Fe17-xAlxC (x=0-8; R identical to Ho, Y or Sm) were fabricated by arc melting. Their structural and magnetic properties have been investigated by means of X-ray diffraction and magnetization measurements. X-ray diffraction patterns demonstrate that all compounds have a single phase with a hexagonal Th2Ni17-type or a rhombohedral Th2Zn17-type structure. The substitution of Al atoms leads to increase in the lattice constants and the unit-cell volume. The Curie temperature is found to change slightly when x<or=3 and then to decrease rapidly with increasing Al concentration. An approximately linear decrease in the saturation magnetization with increasing x is observed by the substitution of non-magnetic Al atoms. The compensation points are observed for the Ho2Fe17-xAlxC samples with x>or=5. Samples of Sm2Fe17-xAlxC with x<or=6 exhibit an easy c-axis anisotropy at room temperature. The room-temperature anisotropy field increases to about 119 kOe when x=2 and then decreases with increasing Al concentration. The substitution of Al for Fe in a small concentration will increase the anisotropy field of Sm2Fe17 carbides. This behaviour is the same as that of Ga and Si.

Magnetic properties of Sm2Fe17−xSix and Sm2Fe17−xSixC compounds

Iron-rich intermetallic compounds Sm2Fe17−xSix and Sm2Fe17−xSixC (x=0, 1, 2, and 3) were studied. The as-prepared compounds are single phase with the rhombohedral Th2Zn17-type structure except for Sm2Fe17C and Sm2Fe16SiC which contain some amounts of α-Fe. The unit cell volumes and saturation magnetization at room temperature are found to decrease linearly with increasing Si concentration x. The Curie temperature Tc is found first to increase and then to decrease with increasing Si content. X-ray diffraction measurements on magnetically aligned powder samples show that the easy magnetization direction of the Sm2Fe17−xSix samples with x≤2 is planar while that of the sample with x=3 is conical. The Sm2Fe17−xSixC samples with x≤3 exhibit an easy c-axis anisotropy at room temperature. The anisotropy field is 83 kOe for x=0 and it rises to 110 kOe at x=1, and then drops with increasing Si concentration to 55 kOe at x=3.

Structural and magnetic properties of H and N modified Y(Fe, M) 12 compounds (M  Ti, V, Mo, Cr, W)

A series of Y(Fe, M) 12 compounds and their hydrides and nitrides, where M  Ti, V, Mo, Cr, W, were prepared single phase. The effects of interstitial H and N atoms on the structural and magnetic properties have been studied by using the X-ray diffraction and magnetic measurements. The hydrides and nitrides still retain the tetragonal structure, but the unit cell volumes are expanded compared to their original counterparts. The saturation magnetization and Curie temperature are increased by both hydrogenation and nitrogenation, whereas the easy c-axis anisotropy related to the Fe-sublattice is enhanced in the hydrides but decreased in the nitrides.