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Magnetic and structural properties of La0.7Sr0.3Mn1-xCrxO3 (x = 0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) have been studied using neutron and x-ray diffraction and magnetic measurements. All samples are found to be of single phase. At 12 K, we find only ferromagnetic ordering for x < 0.30 and coexisting ferromagnetic and antiferromagnetic domains for x ⩾ 0.30. Our magnetic data indicate temperature dependent ferromagnetic to paramagnetic, and likely antiferromagnetic to paramagnetic transitions. We find no evidence of spin glass or cluster glass behavior, only long-range magnetic order with a transition to antiferromagnetic behavior beginning with x = 0.30 and almost completely antiferromagnetic behavior at x = 0.50.

The 295 K powder neutron diffraction patterns and the temperature dependence of the Mossbauer spectra of Nd2Fe17−xTix and Nd2Fe17−xTixNy have been measured. A Rietveld refinement of the neutron diffraction patterns yields the Nd2Fe16.32Ti0.68 and Nd2Fe16.32Ti0.68N2.7 stoichiometries for the two compounds and indicates that titanium occupies only the 6c crystallographic site and nitrogen only the 9e site in the rhombohedral Th2Zn17 structure. The insertion of interstitial nitrogen into Nd2Fe16.32Ti0.68 produces a 6.8% increase in the unit cell volume. The relative areas of the Mossbauer spectral components indicate that iron–iron, iron–titanium, and titanium–titanium 6c–6c dumbbell pairs exist in both of these materials. The magnetic hyperfine fields observed for the iron on the 6c site in the iron–titanium dumbbell pair in both compounds is substantially reduced from that found in Nd2Fe17 and Nd2Fe17N2.6 because of the titanium dumbbell near neighbor. For all the remaining hyperfine parameters there is a ...

The Mossbauer spectra of the Sm 2 Fe 17− x Al x solid solutions, where x is 0, 0.5, 0.75, 1, 3, and 4, which crystallize in the rhombohedral Th 2 Zn 17 structure, have been measured between 85 and 295 K. The spectra have been successfully analyzed with a model based on the binomial distribution of aluminum near neighbors calculated from the aluminum site occupancies derived from neutron diffraction measurements on Nd 2 Fe 17− x Al x solid solutions. This analysis indicates that the Mossbauer spectra are sensitive to the spin reorientation occurring between x values of one and three, confirms that the aluminum site occupancies are independent of the rare-earth element in the R 2 Fe 17− x Al x solid solutions, gives values of the iron site magnetic moments, and reveals an important covalent bonding between iron and its aluminum near neighbors.

The compositional dependence of the Curie temperature of the Tb 2 Fe 17− x Ga x solid solutions shows a primary maximum for x equal to three and a secondary maximum for x equal to eight. The Mossbauer spectra and powder neutron diffraction patterns of Tb 2 Fe 9 Ga 8 indicate that gallium avoids the 9d site, completely fills the 6c site, and occupies preferentially the 18f site over the 18h site. This gallium preferential substitution leads to a nearly ordered two-dimensional antiferromagnetic arrangement of the terbium and iron magnetic moments, an increase in Curie temperature, and a surprisingly sharp Mossbauer spectrum.

The magnetic properties of the rhombohedral Ce 2 Fe 17 − x Ga x solid solutions, with x equal to 0.3, 0.5, 0.7, 1.0, and 2.0, have been studied by magnetic measurements, neutron diffraction, and Mossbauer spectroscopy. Magnetization studies indicate that, as the unit cell volume expands with Ga addition, the Curie temperature increases from 238 K for Ce 2 Fe 17 to 406 K for Ce 2 Fe 15 Ga 2 . Powder neutron diffraction measurements at 295 and 14 K indicate that the Fe moments are both oriented in the basal plane and increase with increasing Ga content. The Mossbauer spectra, which have been fit with a binomial distribution of the near-neighbor environments, indicate that the maximum hyperfine field, H max , increases with increasing Ga content and is largest for the 6c site. The decremental field, ΔH , per added Ga atom is virtually independent of temperature and Ga content, indicating that the next-nearest-neighbor interactions are very small. The compositional dependence of the isomer shifts for R 2 Fe 17 − x M x , where R is Ce or Tb and M is Al, Si, or Ga, is analyzed in terms of volume and chemical terms, the second of which reveals the importance of the electronic configuration of M in understanding its influence on the magnetic properties of these solid solutions. Finally, the similarities and differences in the changes in crystallographic, magnetic, and Mossbauer spectral properties of R 2 Fe 17 − x M x , at low x values, indicate that electronic rather than structural factors are more important in modifying the magnetic properties and indicate the need for extensive band structure calculations on these solid solutions.

We report the structure and properties of iron-containing films deposited on glass substrates maintained at temperatures between 200 and 500 °C. The films investigated were Fe 3 O 4 , Fe 7 C 3 , Fe 3 C 1 and α-Fe, deposited at substrate temperatures of 200, 300, 400 and 500 °C, respectively. The measured SEM grain sizes from these 200–700 nm thick films were in the 50–350 nm range. X-ray diffraction and scanning electron microscopy show larger grains and increased crystallinity in the films deposited at higher substrate temperatures. The larger grain sizes and increased crystallinity are consequences of bulk diffusion and surface recrystallization. The sheet conductivities of the films increase with increasing film deposition temperature, due to coarser grain structures and higher iron to carbon ratios in the higher temperature films. The phases remain unchanged after annealing at 400 °C for 4 h. X-ray diffraction and scanning electron microscopy show evidence of bulk rearrangement and a reduction of thickness in the annealed films.

The magnetic properties of a series of Tb 2 Fe 17− x Al x solid solutions, with x equal to 0.00, 1.00, 1.98, 3.14, 4.08, 5.10, 6.06, 7.16, and 8.12, have been studied by magnetic measurements and Mossbauer spectroscopy. Magnetization studies indicate that the Curie temperature increases from 420 K in Tb 2 Fe 17 to a maximum of 475 K in Tb 2 Fe 13.86 Al 3.14 . The magnetization results indicate an antiferromagnetic coupling of the terbium sublattice with the iron sublattice at low temperature. The magnetically ordered Mossbauer spectra have been fit with a binomial distribution of near neigbors. The weighted average maximum hyperfine field, H max , decreases by 12 kOe per aluminum at 85 K. The decrease in hyperfine field is due to the dilution of the magnetic moments by aluminum. The weighted average decremental field, Δ H , decreases by 2 and 1 kOe per aluminum at 85 and 295 K, respectively. The compositional dependence of the decremental field indicates the presence of RKKY type spatial spin oscillation in the 4s conduction band, an oscillation which is modified by the presence of aluminum. The weighted average isomer shift increases by 0.016 and 0.010 mm/s per aluminum at 85 and 295 K, respectively, because of both the screening of the 4s electrons by the 3d electrons due to interband mixing of the 3d band with the valence band of aluminum, and the unit cell volume expansion upon aluminum substitution.

Thin (50–80 nm) iron carbide films were grown on carbon-coated copper grids in an r.f. glow discharge using iron pentacarbonyl and hydrogen as starting materials. The substrate temperatures were varied in the range 200–500 °C. The microstructure and phases present in these films are compared with the corresponding results previously obtained by X-ray diffraction, atomic force microscopy, scanning electron microscopy and Auger electron spectroscopy for thick (200–1100 nm) films grown on glass substrates. Transmission electron microscopy studies show that the 50–80 nm films contain a mixture of phases at all deposition temperatures. Transmission electron micrographs of annealed films and films deposited at high temperatures show a clear indication of grain growth.

A series of NdDyFe/sub 17-x-y/Co/sub x/Si/sub y/ solid solutions with x = 2 and 3 and y=0.5,1.0,and 1.5 were prepared by induction melting stoichiometric amounts of high-purity elements. The postannealed samples consist of two phases belonging to the space groups R3 m and P6/sub 3//mmc. The lattice parameters and the unit cell volumes were calculated from the refinements of the magnetic and structural unit cells using the FULLPROF version of the Rietveld program. For a fixed content of Co, the maximum Curie temperatures (305/spl deg/C to 405/spl deg/C) were observed in samples with y=1 and having two phases, a disordered rhombohedral (DR) structure and a disordered hexagonal (DH) structure. An increase in the Curie temperature of 70/spl deg/C per atom of cobalt is observed in NdDyFe/sub 17-x-y/Co/sub x/Si/sub y/ with y=1 and x /spl les/ 3, suggesting that with a suitable choice of rare earths this DR phase may be a promising candidate for high-energy product permanent magnets. The magnetization versus temperature (M versus T) plots of the solid solutions, which consist of two phases, exhibit only a single magnetic ordering transition temperature.

The Mossbauer effect spectra of Nd2Fe17H3, Nd2Fe17H5, and Nd2Fe17N3 have been measured at several temperatures between 85 and 295 K and fitted with a model which is similar to that used for the analysis of the Mossbauer effect spectra of Nd2Fe17 and Nd2Fe17N2.6. The weighted average isomer shift increases in going from Nd2Fe17 to its hydrides and nitride, an increase which results mainly from the lattice expansion. The changes in the individual isomer shifts upon hydrogenation may be understood in terms of the expansion of the Wigner-Seitz cell volume and the presence of hydrogen or nitrogen near neighbors at a specific site. The 295 K weighted average hyperfine field increases from 157 kOe in Nd2Fe17 to 243 kOe in Nd2Fe17H3, 280 kOe in Nd2Fe17H5, and 318 kOe in Nd2Fe17N3, a sequence determined by the Curie temperatures. In contrast, the weighted average hyperfine field at 85 K and the saturation magnetization at 5 K for Nd2Fe17H3 are lower than those of Nd2Fe17, presumably because of thec-axis lattice contraction which occurs upon hydrogenation of this compound. The main difference between the effect of hydrogenation and nitrogenation resides in the substantial increase observed for the 9d and 18h hyperfine fields upon nitrogenation.

The magnetic properties of a series of Ce2Fe17−xAlx solid solutions with x equal to 0.00, 0.88, 2.06, 2.81, 3.98, 5.15, 6.08, 7.21, 8.20, 9.08, 9.84, and 10.62 have been studied by magnetic measurements, neutron diffraction, and Mossbauer spectroscopy. The compounds crystallize in the rhombohedral Th2Zn17‐type structure. Magnetization studies indicate that the Curie temperature increases uniformly from 238 K for Ce2Fe17 to 384 K for Ce2Fe14Al3 and then decreases at higher aluminum content. Powder neutron diffraction results, obtained at 295 K, indicate that aluminum avoids the 9d site for all x values and preferentially occupies the 18h site at low aluminum content. Aluminum shows a marked preference for the 6c site for x≳6. The room‐temperature iron magnetic moments increase from x=0 to 2 and then decrease for x≳2. The Mossbauer spectra have been fit with a binomial distribution of the near‐neighbor environments in terms of a maximum hyperfine field, Hmax, for an iron with zero aluminum near neighbors, a...

A series of Nd2−yDyyFe17−xSix solid solutions with x=0, 1, 2, and 3 and y=0, 0.5, 1.0, 1.5, and 2.0 were prepared by induction melting stoichiometric amounts of high-purity elements. The x-ray diffraction data confirmed that the postannealed samples are 2:17 intermetallics of the R3m space group. The lattice parameters and unit-cell volumes were calculated using FULLPROF to analyze the neutron diffraction (ND) data. It was observed that for a particular y, the unit-cell volume decreased almost linearly with increasing silicon content (x⩽3), as is observed for single rare-earth 2:17 intermetallic compounds. For a given x, the cell volume decreased almost linearly with the increasing replacement of neodymium with dysprosium. The ND studies revealed additional density along the c-axis chains of Fe dumbells and rare-earth atoms. The perfect a-b-c stacking of the CaCu5 layers with a regular one third replacement of the rare-earth atoms by Fe dumbells appear to be broken, resulting in a disordered rhombohedral...

The Mossbauer effect spectra of Y2Fe17 and Y2Fe17N2.6, obtained at 85 K, are analyzed with a model consistent with their crystallographic structures and band structure calculations of their magnetic moments. The increases in the individual site isomer shifts and hyperfine fields upon nitrogenation correlate well with the increases in both the individual Wigner-Seitz cell volumes and the magnetic moments. The spectral analysis, which requires ten sextets, indicates that the magnetization lies in a general direction in the hexagonal basal plane of these compounds.

The magnetic properties of a series of Nd2Fe17−xAlx solid solutions, with x equal to 2.04, 4.01, 5.97, 7.94, and 9.06, have been studied by magnetic measurements, neutron diffraction, and Mossbauer spectroscopy. Magnetization studies indicate that the Curie temperature increases from 330 K in Nd2Fe17 to a maximum of ∼470 K at an x of 3.5. The compounds crystallize in the Th2Zn17 structure with lattice parameters and unit cell volumes which increase linearly with increasing aluminum content. The neutron diffraction results indicate that aluminum atoms are excluded from the 9d site, prefer the 18h site at low aluminum content, and prefer the 6c and 18f sites at high aluminum content. At 10 K the magnetic moments of the iron and neodymium atoms are collinear and take up a basal orientation at all aluminum contents. The moments decrease with increasing aluminum content and the magnetic moments per unit cell at 10 K are in excellent agreement with the 4.2 K saturation magnetization values. At 295 K the Nd2Fe17...

An x‐ray diffraction study of the substitution of gallium in Tb2Fe17 to form the Tb2Fe17−xGax solid solutions indicates that the compounds adopt the rhombohedral Th2Zn17 structure. The unit cell volume and the a‐axis lattice parameter increase linearly with increasing gallium content. The c‐axis lattice parameter increases linearly from x=0 to 6 and then decreases between x=7 and 8. Magnetic studies show the Curie temperature increases by ∼150° above that of Tb2Fe17 to reach a maximum between x=3 and 4, and then decreases with further increases in x. Neutron diffraction studies of Nd2Fe15Ga2 and Tb2Fe17−xGax, with x equal to 5, 6, and 8, indicate that the gallium completely avoids the 9d site, occupies the 6c ‘‘dumbell’’ site only at high values of x and strongly prefers the 18f site at high values of x. The magnetic neutron scattering indicates both that the terbium sublattice magnetization couples antiferromagnetically with the iron sublattice and that there is a change in easy magnetization direction f...

The Mossbauer spectra of Th2Fe17 and Th2Fe17N2.6 have been measured at various temperatures between 85 and 295 K and analyzed with a model that is based on the Wigner–Seitz cell environment of each iron site, the orientation of the magnetization, and the magnetic moments as determined from either neutron‐diffraction measurements or band‐structure calculations. Upon nitrogenation of Th2Fe17, the 85 K weighted average isomer shift increases from 0.037 to 0.156 mm/s and further the isomer shifts of the four crystallographically distinct sites increase in agreement with the increase observed in their Wigner–Seitz cell volumes and the presence of a nitrogen near neighbor for two of the sites. The nonmagnetic thorium in Th2Fe17N2.6 yields an easy axis of magnetization which, in contrast to magnetic rare earths in R2Fe17 and R2Fe17Nx, is in a general basal direction and not oriented along one of the basal axes. The isomer shift and its temperature dependence for both Th2Fe17 and its nitride are very similar to those observed in related rare‐earth R2Fe17 compounds and their nitrides. Upon nitrogenation of Th2Fe17, the 85 K weighted average hyperfine field increases from 256.3 to 336.5 kOe. However, the increases on the 6c and 18f sites are smaller than those observed on the 9d and 18h sites; changes which are in agreement with changes in the magnetic moments observed by neutron diffraction and calculated for the nitrogenation of Nd2Fe17, Gd2Fe17, and Y2Fe17.The Mossbauer spectra of Th2Fe17 and Th2Fe17N2.6 have been measured at various temperatures between 85 and 295 K and analyzed with a model that is based on the Wigner–Seitz cell environment of each iron site, the orientation of the magnetization, and the magnetic moments as determined from either neutron‐diffraction measurements or band‐structure calculations. Upon nitrogenation of Th2Fe17, the 85 K weighted average isomer shift increases from 0.037 to 0.156 mm/s and further the isomer shifts of the four crystallographically distinct sites increase in agreement with the increase observed in their Wigner–Seitz cell volumes and the presence of a nitrogen near neighbor for two of the sites. The nonmagnetic thorium in Th2Fe17N2.6 yields an easy axis of magnetization which, in contrast to magnetic rare earths in R2Fe17 and R2Fe17Nx, is in a general basal direction and not oriented along one of the basal axes. The isomer shift and its temperature dependence for both Th2Fe17 and its nitride are very similar to t...

We have studied the structural and magnetic properties of La0.7Sr0.3Mn1-xNixO3 (x=0.05, 0.10, 0.20, 0.30, and 0.40) perovskites using x-ray and neutron diffraction and magnetic measurements. To our knowledge, there exists no neutron diffraction data available for this group of perovskite compositions. Neutron (λ = 1.479Å) and x-ray (λ = 1.5481Å; Cu Kα) powder diffraction indicate that for x ≥ 0.1 all samples are two-phase with a rhombohedral perovskite structure (space group R-3c) and a small amount of NiO (space group Fm3m). Neutron diffraction data for the perovskite phase at 12K and 300K show ferromagnetic ordering for x ≤ 0.2 and antiferromagnetic ordering for x = 0.4. However, for x = 0.3, neutron diffraction data at 12K show coexisting ferromagnetic and antiferromagnetic ordering while at 300K no magnetic ordering is found. Magnetic measurements indicate that the Curie temperature decreases with increasing Ni content. The NiO phase for all samples was found to have antiferromagnetic ordering at 12K and 300K. The magnetic measurements are consistent with the neutron diffraction data and together indicate long-range magnetic ordering for samples at low temperature and transitions from ferromagnetic to paramagnetic to antiferromagnetic ordering for samples at room temperature.

A neutron‐diffraction study of Nd2Fe14−xSixB has shown that silicon preferentially occupies the 4c site in the transition‐metal sublattice in Nd2Fe14B. Silicon also exhibits a moderate preference for the 8j1 site, is almost excluded from the 16k2 site, and avoids the 16k1, 8j2, and 4e sites. The silicon site occupancy is correlated with a preference for a silicon atom to have rare‐earth atoms in its coordination environment. The Mossbauer spectra of Nd2Fe14−xSixB have been fit with a model which takes into account the distribution of near‐neighbor environments of an iron atom due to the presence of silicon. These fits show that the substitution of silicon in the near‐neighbor environment of an iron atom primarily influences the long‐range contributions to the hyperfine field experienced by the iron. The mechanism for the increase in the Curie temperature when silicon is added to Nd2Fe14B‐type magnets is more subtle than previously believed, but can be explained by the relative decrease in the proportion o...

The neutron diffraction powder patterns of Pr2Fe17 and Pr2Fe17N2.6 have been measured at 295 K and refined within the Th2Zn17 structure type to give the structural changes which occur upon nitrogenation; changes which include a 6.4% expansion of the unit cell volume. The Mossbauer spectra of Pr2Fe17 and Pr2Fe17N2.6 have been measured between 85 and 295 K and analyzed with a model which is based on the Wigner–Seitz cell environment of each iron site, the basal orientation of the magnetization, and a comparison with the Mossbauer spectra of Nd2Fe17 and Nd2Fe17N2.6. Upon nitrogenation of Pr2Fe17, the 85 K‐weighted average isomer shift increases from 0.049 to 0.156 mm/s, and the isomer shifts of the four crystallographically distinct iron sites increase in agreement with the increase found in their Wigner–Seitz cell volumes and the presence of a nitrogen near‐neighbor for the 18f and 18h sites. The temperature dependence of the isomer shifts indicates an increase in covalency upon the formation of the nitride...

A detailed analysis of approximately fifty iron-57 Mossbauer spectra of R 2 Fe 14 B and R 2 Fe 14 C, obtained as a function of rare-earth and temperature, reveals that the iron 8j 2 site has the largest hyperfine field of the six crystallographically distinct iron sites present in these compounds. This experimental result does not agree with a recent calculation of the hyperfine fields in R 2 Fe 14 B which indicates that the 16k 2 site has the largest hyperfine field. The inconsistency of this calculation with the experimentally measured hyperfine fields leads to the conclusion that the calculated hyperfine fields must be accepted with caution.

A systematic study of the magnetic moments and hyperfine interactions of the LaNi5–xFex compounds was performed using the spin-polarized tight-binding-linear-muffin-tin-orbital methods (TBLMTO). The calculated results were compared with neutron diffraction and Mossbauer experimental data and found to be in good agreement. Fe atoms exhibit more localized magnetic moments in LaNi5–xFex when the Fe content x is lower than 1.0. The calculated magnetic moments of the Fe atoms approach values as large as 2.5μB due to the dilution effect. The strong s–d hybridization between the Ni and La atoms and the neighboring Fe in the Fe-substituted samples results in a large transferred valence contribution to the total hyperfine field. It is found that the Fe and Ni magnetic moments decrease abruptly at a unit cell volume which is 5% smaller than the observed volume in LaNi4Fe due to the instability of the Fe magnetic moment. LaNi5 becomes ferromagnetic when the unit cell volume is larger than its original volume.

The Mossbauer spectra of Nd2Fe17 and Nd2Fe17N2.6 have been measured at various temperatures between 78 and 295 K and analyzed with a model that is based on the Wigner–Seitz cell environment of each iron site, the orientation of the magnetization, and the magnetic moments as determined from either neutron‐diffraction measurements or band‐structure calculations. Upon nitrogenation of Nd2Fe17, the weighted average isomer shift increases from 0.060 to 0.164 mm/s and further the isomer shifts of the four crystallographically distinct sites increase in agreement with the increase observed in their Wigner–Seitz cell volumes and the presence of a nitrogen near neighbor for two of the sites. Upon nitrogenation of Nd2Fe17, the weighted average hyperfine field increases from 292.3 to 333.8 kOe. However, the increases on the 6c and 18f sites are much smaller than those observed on the 9d and 18h sites; changes which are in agreement with calculated changes in the magnetic moments upon nitrogenation of Nd2Fe17, Gd2Fe17, and Y2Fe17. The temperature dependence of the isomer shifts indicates an increase in covalency upon the formation of the nitride.

The Mossbauer spectra of R 2 Fe 14 B, where R is La, Tb, Dy, Ho and Lu, have been measured at 295 K and the Mossbauer spectra of R 2 Fe 14 C, where R is Nd, Ho and Gd, have been measured at various temperatures between 85 and 295 K. All of the resulting spectra have been successfully analyzed with the same model used earlier to fit the spectra of various related compounds. The results indicate that the weighted average hyperfine field increases uniformly from La to Gd and decreases uniformly from Gd to Lu in R 2 Fe 14 B, as was found earlier for R 2 Fe 14 C. The weighted average isomer shift decreases by 0.04 mm/s in going from La 2 Fe 14 B to Lu 2 Fe 14 B, because of a decrease in the unit cell volume and an increase of the number of electrons in the unit cell, a decrease which corresponds to a 13.5% increase in the electron density. The use of the same model for both the Nd, Gd, Tb, Dy, Ho and Lu borides and carbides permits a detailed comparison of the Mossbauer hyperfine parameters in the two series of compounds. There is a linear correlation of the hyperfine fields at each of the sites in these two series of compounds, indicating that the replacement of boron by carbon has a long-range effect on the magnetic exchange within these materials. There is a correlation of the isomer shifts of the 8j 1 , 8j 2 and 16k 2 sites in the two series of compounds. In contrast the isomer shift of the 16k 1 site show the chemical influence of replacing boron by carbon. With the expected exception of the 4c site there is a correlation between the quadrupole interactions in the two series of compounds. The Nd 2 Fe 14 B and Nd 2 Fe 14 C compounds have relatively low effective Mossbauer temperatures as compared to the borides and carbides with the heavier rare-earth elements.

The crystallographic and magnetic properties of LaNi5−xMnx with x=1, 1.5, and 2, have been investigated using x-ray and neutron diffraction, vibrating sample magnetometer and superconducting quantum interference device measurements. All the samples crystallize in the hexagonal CaCu5-type (P6/mmm) structure. Manganese atoms preferentially occupy the 3g site in the LaNi5 structure. The bulk magnetization of the LaNi5−xMnx powder samples decreases rapidly as nickel is replaced by manganese. A ferrimagnetic model is applied to describe the magnetic structure of the LaNi5−xMnx samples for x=1.5 and 2. A ferromagnetic model gives the best fit of the neutron diffraction data for the LaNi4Mn sample.

The magnetic and crystallographic properties of LaNi/sub (5-x)/Fe/sub x/ samples (1/spl les/x/spl les/1.4) have been studied by X-ray diffraction, neutron diffraction, SQUID and Mossbauer spectroscopy. Samples with x/spl ges/1.2 display typical ferromagnetic behavior. The substitution of iron for nickel in LaNi/sub 5/ increases the unit cell volume and Curie temperature. The majority (>90%) of the Fe atoms appear to occupy the 3g site. Induced Ni magnetic moments at 30 K have been calculated using the bulk magnetization data and iron magnetic moments.

The Mossbauer spectra of Pr2Fe14B and Gd2Fe14B have been measured from 85 to 295 K and fit with a second order approximation in which the angle, ϕ, between the principal axis of the electric field gradient and the easy-axis of magnetization has been fixed by the positions of the near-neighbor rare-earth atoms. The coordination environment for each of the six iron sites in these materials has been determined from the Wigner-Seitz cell and used in the spectral analysis. The hyperfine parameters resulting from the above fit are in agreement with the structural and electronic properties of these compounds and also agree well with those determined in our earlier studies of Nd2Fe14B and Y2Fe14B. The magnetic hyperfine fields for the different sites are similar in the Y, Pr, and Nd compounds but are, as expected, higher in the Gd compound because of the much higher spin-multiplicity associated with Gd. The hyperfine fields on the 8j 1 and 4c sites, which have the most rare-earth near-neighbors show, as expected, the largest variation with rare-earth atom. The quadrupole interactions are constant with temperature and the absolute value of the quadrupole interactions on the 8j 2 and 4e site are found to be the largest, as is consistent with the highly distorted environment of these sites With the possible exception of the 4c site, the quadrupole interaction shows little variation with rare-earth atom. The isomer shift for each site in each compound varies linearly with temperature, as expected, for the second-order Doppler shift and gives effective Mossbauer masses between 62 and 67 g/mole. The weighted average isomer shift is similar in each of these compounds, but the isomer shifts associated with some of the specific sites in Gd2Fe14B are rather different than in the Y, Pr, and Nd compounds.

A series of Nd2Fe17−xMnx solid solutions with x values between 0 and 6 were prepared and analyzed using magnetic measurements, neutron diffraction, and Mossbauer spectroscopy. All of the Nd2Fe17−xMnx samples crystallized in the Th2Zn17−x-type rhombohedral structure. The lattice parameters and unit cell volumes decrease with increasing manganese content up to ∼x equal to 2, and then increase for higher manganese content. The magnetizations of Nd2Fe17−xMnx decrease with increasing manganese content and Nd2Fe17−xMnx is paramagnetic at room temperature for x greater than 3. The Curie temperature in Nd2Fe17−xMnx solid solutions is maximum for x equal to 0.5 and decreases at a rate of ∼10° per substituted manganese up to x equal to 3, after which it drops sharply. These results are discussed in terms of the manganese site occupancies in Nd2Fe17−xMnx.

The magnetic properties of a series of Tb2Fe17−xAlx solid solutions, with nominal x compositions of 0, 2, 3, 4, 5, 6, 7, and 8, have been studied by neutron diffraction and Mossbauer spectroscopy. Neutron‐diffraction data indicate that the compounds all crystallize with the Th2Zn17 structure and that the aluminum atoms are excluded from the 9d site and show a distinct preference for the 6c site only for an aluminum content greater than 6. The unit‐cell volume increases by approximately 1% per aluminum atom substituted in the formula unit. The magnetic moment per formula unit, measured at 295 K, shows very little change for x less than or equal to 4, but decreases rapidly with increasing aluminum content for higher values of x. Mossbauer spectral results indicate that all the samples are ferromagnetically ordered at 85 K. However, at 295 K Tb2Fe9Al8 is paramagnetic and Tb2Fe10Al7 is either paramagnetic or has at most very small ferromagnetic moments. An analysis of the magnetic spectra with a basal magneti...

The Mossbauer spectra of Sm2Fe17 and Ho2Fe17 and their nitrides have been measured between 295 and 85 K and analyzed with a model which is consistent with our earlier work on R2Fe17 and R2Fe17Nx compounds, where R is Pr, Nd, and Th. This model is completely consistent throughout these rare‐earth compounds and is in agreement with the crystallographic changes occurring upon nitrogenation and with the prediction of band structure calculations. The dramatic increase in Curie temperature in the nitrides results from the expansion of the crystallographic lattice, an expansion which is mainly centered on the 9d and 18h iron sites as is indicated by the increase of their Wigner–Seitz cell volumes upon nitrogenation. The 9d and 18h sites show a larger enhancement of their hyperfine fields as compared to the 6c and 18f sites as a result of improved ferromagnetic exchange between these sites and their near neighbors because of the lattice expansion and the consequent reduced iron 3d‐iron 3d overlap.

Neutron-diffraction and Mossbauer effect studies of Y/sub 2/Fe/sub 14-x/Si/sub x/B, where x is 0.28, 0.67, and 1.87, show that silicon preferentially occupies the 4c site in the R/sub 2/Fe/sub 14/B structure. If the breaking of short iron-iron bonds is the mechanism for the increase in the Curie temperature of R/sub 2/Fe/sub 14-x/Si/sub x/B, then the bonds most responsible for the increase are those between iron atoms on the 16k/sub 2/ and 4c sites. >

The Mossbauer spectra of Nd2Fe17 and Nd2Fe17N2.6 have been measured as a function of temperature between 85 and 295 K. The spectral fits and hyperfine parameters for Nd2Fe17 are consistent with a Wigner-Seitz analysis of the iron near-neighbor environment. The presence of nitrogen has a major effect on the hyperfine parameters of the iron on the 18f and 18h sites, the only iron sites which have nitrogen near neighbors in Nd2Fe17N2.6.

The magnetic structures of a series of Y2(Fe1−xMnx)14B samples, with x equal to 0.03, 0.10, 0.25, and 0.37, have been studied by powder neutron diffraction and Mossbauer spectroscopy. Y2(Fe0.97Mn0.03)14B and Y2(Fe0.9Mn0.1)14B are ferromagnetic at both 295 and 85 K, Y2(Fe0.63Mn0.37)14B is paramagnetic at both 295 and 85 K, whereas Y2(Fe0.75Mn0.25)14B is paramagnetic at 295 K and is partially ordered at 78 K. The magnetic structure of Y2(Fe0.75Mn0.25)14B is explained in terms of the preferential Mn occupancy of the transition metal 8j2 site in the Y2Fe14B structure. Small amounts of Mn located in this site are very effective in disrupting the long‐range ferromagnetic coupling.

The 57Fe Mossbauer‐effect spectra of the series of hard magnetic materials, R2Fe14C, where R is Nd, Gd, Tb, Dy, Ho, and Lu, have been measured at 295 K. All of these carbides exhibit uniaxial magnetic anisotropy. The spectra resemble those obtained for the related R2Fe14B compounds and have been fit with the model used earlier for Nd2Fe14B. The magnitude of the hyperfine field on each site, as a function of rare earth, parallels the Curie temperature; the maximum hyperfine fields and the maximum Curie temperature are observed for Gd2Fe14C. A linear correlation is observed between the hyperfine fields on the six sites in the analogous borides and carbides; however, these fields are systematically smaller in the carbides. The decrease in the tetragonal unit cell c‐axis length in the carbides apparently reduces the exchange interactions between the 8j and 16k iron layers and hence reduces the moments. The isomer shift on each site decreases as the atomic number of the rare earth increases, whereas the quadru...

A neutron‐diffraction investigation of a series of Pr2(Fe1−xMnx)14B samples, with x values of 0.00, 0.11, 0.22, 0.30, and 0.35, reveals a preference for the manganese to occupy the 8j2 transition‐metal site,the transition‐metal site with the largest Wigner–Seitz cell volume. Similar site occupancies have been reported previously for Er2(Fe1−xMnx)14B and Y2(Fe1−xMnx)14B. An analysis of the 295‐K Mossbauer spectrum of Pr2(Fe0.89Mn0.11)14B indicates that the internal hyperfine fields on the six iron sites are more substantially reduced from those found in Pr2Fe14B than would be expected from a simple magnetic dilution with manganese. The extent of the field reduction for a specific site increases with the number of manganese near neighbors for the site. Fits of the Mossbauer spectra of Pr2(Fe0.78Mn0.22)14B, Pr2(Fe0.70Mn0.30)14B, and Pr2(Fe0.65Mn0.35)14B, which are paramagnetic at room temperature, give quadrupole splittings consistent with the quadrupole interactions in Pr2Fe14B.

We have studied the structural and magnetic properties of La0.7Sr0.3Mn1−xNixO3 (x = 0.05, 0.1, 0.20, 0.30, and 0.40) perovskites using x-ray and neutron diffraction and magnetic measurements. Our data consist of neutron (λ = 1.479 A) and x-ray (λ = 1.5481 A; Cu Kα) powder diffraction and magnetization measurements. We previously suggested these systems transition from ferromagnetic to antiferromagnetic ordering with the intermediate concentrations containing coexisting domains of ferromagnetically and antiferromagnetically ordered states. Upon further detailed examination, we find that the samples are homogeneous and that neutron data can be fitted to a single long-range magnetically ordered state. The compositional dependent changes are driven by a shift in the dominant near neighbor interaction from ferromagnetic to antiferromagnetic. In the intermediate compositions, peaks previously identified as due to antiferromagnetic ordering, in fact arise from charge ordering; the system remains in a ferromagnet...

Thin iron carbide films were prepared by introducing iron penta carbonyl (FeCO5) and hydrogen (H2) into a glow discharge. The films are of potential interest in corrosion and wear resistant applications. X-ray diffraction data of films (≈ 7000 Å thick) deposited on glass at 300°C evidenced only Fe7C3. Thinner films were required for examination by analytical and high resolution transmission electron Microscopy. Therefore, two sets of films (“thin” < 200 Å and “thick” ≈ 800 Å) were plasma-deposited on carbon or holey carbon films supported on copper grids. The thin TEM specimens exhibited a fine texture and gave rise to ring diffraction patterns, whereas the thick TEM specimens evidenced two types of structure: (i) half-Micron sized grains separated from one another by 1–2 Microns on the support, although sometimes interconnected by single crystal platelets and (ii) 300 Å grapelike clumps of 100–200 Å crystals, each individually surrounded by a 50 Å non-crystalline coating. The latter structure may result from a post-formation oxidation process which expels carbon from the iron phase into grain boundaries.

Thin Mirror-like iron carbide films were prepared by introducing iron pentacarbonyl [Fe(CO)5] and hydrogen [H2] into a glow discharge. The deposition temperatures were varied from 200–500°C. The iron to carbon ratios of the resulting films were controlled by adjusting the gas flow ratios. The Microstructure and phase transformations occurring in these films were studied before and after annealing at 400°C for four hrs. Characterization techniques used included x-ray diffraction, electron diffraction, Auger spectroscopy and atomic force Microscopy.X-ray diffraction data of plasma-deposited films on glass substrates maintained at 400°C showed the presence of only Fe3C. However, the x-ray diffraction data of films on carbon coated glass, and transmission electron microscopy selected area diffraction patterns of films on carbon coated copper grids indicated the presence of a second phase, the closely related Metastable Fe7C3, as well as small amounts of Fe3O4. Atomic force microscopy of crystallites on the surface of films deposited at 400°C and annealed at 400°C for four hours revealed a periodic structure of oblate spheroids. The Measured spacings and angle, when compared to projected models of high reticular density planes, suggested the surface to have a structure corresponding to that of bulk FesC or Fe3C or Fe7C3. However the data were not of sufficient quality to unambiguously determine such.

The selected area diffraction information in a single HREM image (Fig. 1) of iron carbide, plasma-deposited onto a carbon support film at 300°C is examined. By “selected area diffraction information” we mean power spectra of selectively digitized regions of the negative. The amount of post microscope diffraction analysis that can be done from a single HREM negative is thus illustrated. It is important for us to know whether these crystals belong to a single phase or whether mixtures of phases are present in these films. X-ray characterization of films deposited on glass substrates at the above deposition temperature have always indicated only Fe7C3. Auger depth profiling data from such films on glass and on carbon support films, along with electron diffraction data from these specimens have indicated the presence of some Fe3O4 in these films as well.Six areas of the negative that showed cross-fringes were digitized and are shown in Fig. 2.

A series of Sm2−xTbxFe17−ySiy solid solutions with x=0, 1, and 1.5 and y=1, 2, and 3 were prepared by induction melting stoichiometric amounts of high purity elements. The x-ray diffraction data confirm that the postannealed samples are 2:17 intermetallics of the R3m space group. The lattice parameters and the unit cell volumes were calculated using a modified Rietveld program. The fitted intensities showed behavior related to a disordered rhombohedral structure as inferred from neutron data. It was observed that for a particular y, the unit cell volume decreased almost linearly with increasing Tb content (x=0, 1, and 1.5). The unit cell volume decreases with increasing Si content (y) for a particular x as is also observed for the single rare-earth 2:17 compounds. The Curie temperature measurements show that with increasing Tb content x a decrease in the Curie temperatures of about 3% for y=1, 10% for y=2, and 15% for y=3 was observed. For a particular x, a nearly linear type increase in the Curie temper...

The Mossbauer spectra of ErFe 3 obtained at 295 and 85 K are analyzed within a model based on previous neutron diffraction measurements. The hyperfine fields and thus the Fe magnetic moments are found parallel to the b axis of the unit cell at 295 K and canted by 57° from the c axis at 85 K. The isomer shifts for the Fe sites are in agreement with the calculated Wigner-Seitz cell volumes.

Three samples of Nd2Fe16TiCx, with x equal to 0.0, 0.3, and 2.8, with the Th2Zn17‐type rhombohedral structure, have been studied by powder x‐ray and neutron diffraction, magnetic measurements, and Mossbauer spectroscopy. Nd2Fe16Ti and Nd2Fe16TiC0.3 were synthesized by induction melting stoichiometric amounts of the constituent elements, whereas Nd2Fe16TiC2.8 was synthesized by methane‐derived gas phase insertion of carbon into finely ground Nd2Fe16Ti at 600 K. The neutron diffraction determined titanium site occupancies are similar in both Nd2Fe16Ti and Nd2Fe16TiC2.8 in which titanium preferentially occupies the 6c transition metal site. In contrast, the titanium occupancies in Nd2Fe16TiC0.3 are markedly different in that titanium avoids the 6c transition metal site and randomly occupies the other three transition metal sites. This difference in occupancies most likely occurs because the titanium diffusion rate during the quenching of Nd2Fe16TiC0.3 is affected by the presence of carbon in the melt. Even t...

Six samples of Ce2Fe17−xGax with nominal Ga content x equal to 0, 0.3, 0.5, 0.7, 1.0, 2.0 have been studied by powder neutron diffraction at room temperature. Both crystalline and magnetic refinements have been carried out. All six samples adopt the Th2Zn17‐type rhombohedral structure. The only additional phase found is α‐iron. Gallium atoms are found to have high affinity for the iron 18h site, and are absent from the 9d and 18f sites. The Ga substitution for Fe leads to an expansion of both the a and c axes. The Curie temperature increases from 238 K for Ce2Fe17 to 406 K for Ce2Fe15Ga2. Magnetic refinements on the samples with x=0.3, 0.5, 0.7, 1.0, and 2.0 reveal that the magnetic moments of the four Fe sites are in the basal plane and that their values increase with increasing Ga content.

The neutron diffraction powder patterns of Pr2Fe17 and Pr2Fe17N2.6 have been measured at 295 K and refined within the Th2Zn17 structure type to give the structural changes which occur upon nitrogenation; changes which include a 6.4% expansion of the unit cell volume. The Mossbauer spectra of Pr2Fe17 and Pr2Fe17N2.6 have been measured between 85 and 295 K and analyzed with a model which is based on the Wigner–Seitz cell environment of each iron site, the basal orientation of the magnetization, and a comparison with the Mossbauer spectra of Nd2Fe17 and Nd2Fe17N2.6. Upon nitrogenation of Pr2Fe17, the 85‐K‐weighted average isomer shift increases from 0.049 to 0.156 mm/s, and the isomer shifts of the four crystallographically distinct iron sites increase in agreement with the increase found in their Wigner–Seitz cell volumes and the presence of a nitrogen near‐neighbor for the 18f and 18h sites. The temperature dependence of the isomer shifts indicates an increase in covalency upon the formation of the nitride...

After nearly twenty years of theoretical and experimental attempts to understand the mutual effects of superconductivity and magnetism on each other, the existence of long-range order of both kinds in the same material was finally established recently with the advent of the families of ternary compounds which have come to be known as “magnetic superconductors” [1,2]. The general use of this term does not necessarily imply a simultaneous coexistence (e.g., at a given temperature) of long-range magnetic order and superconductivity, although the very existence of superconductivity in crystals which contain ordered lattices of magnetic ions is itself initially very surprising and is believed to be due to the relative weakness of the exchange spin-flip (and therefore pair-breaking) interaction between the closed shell (necessarily f-like) of electrons on the magnetic ions and the conduction-band electrons. Nevertheless, in many of these compounds, magnetic long-range order (LRO) can simultaneously coexist with superconductivity over certain temperature ranges. This is particularly true of the case in which the magnetic LRO is of the antiferromagnetic type. The case of ferromagnetic LRO leads to the phenomenon of “re-entrance” and will be discussed in detail later. The best studied families of these compounds are the ternary borides with the chemical formula ReRh4B4 (where RE is a rare earth ion), and the Chevrel phase compounds with the formula REMo6S8 or REMo6Se8. There exist by now several review articles on these extremely interesting classes of materials, which the reader may consult for more detailed experimental information [3,4]. In this article, we shall concern ourselves with neutron scattering studies of these compounds. Reviews of the recent theoretical developments of the subject may be found in many other papers of this symposium.

A new magnetic phase has been observed in as-cast and melt-spun Nd-Fe and Pr-Fe alloys with a Curie temperature around 265°C. SEM studies show the presence of this phase in the form of spherical and elongated particles 5 μ m in size with a composition having a ratio of Fe/Nd=4:1. This phase is believed to be a ternary Nd-Fe-O phase stabilized with oxygen. The phase appears to have a high anisotropy leading to coercivities of about 6 kOe in as-cast samples at room temperature. The Mossbauer spectra of this phase can be fitted to four Fe sites with magnetic moments ranging from 1.7 to 2.54μ B .